Control of personal care products based on skin moisture level

Abstract

According to one aspect, a personal care device 500 is provided that includes a device 100 for determining a moisture level in a subject's skin. The device 100 includes a first electrode 102 configured to contact the subject's skin, a second electrode 104 configured to contact the subject's skin, a high frequency RF generator unit 106 configured to provide an RF voltage between the first and second electrodes at each of a plurality of different frequencies to cause a current to flow from the first electrode through the subject's skin to the second electrode, a skin impedance measurement unit 108 configured to measure the impedance of the skin between the first and second electrodes at each of the plurality of different frequencies, and a processing unit 110 in operative communication with the RF generator unit and the skin impedance measurement unit, the processing unit configured to determine the moisture level of the skin based on a slope of a difference in skin impedance at each of the plurality of different frequencies. A control signal is generated based on the moisture level of the skin to control an operating parameter of the personal care device.

Description

[Technical Field]

[0001] The present invention relates to a personal care device and a method of controlling a personal care device based on a determined moisture level on a subject's skin, and more particularly based on a moisture level on a subject's skin determined based on impedance data. [Background technology]

[0002] The safety and effectiveness associated with personal care devices, such as skin treatment devices, may depend on the condition of the skin, such as whether the skin is wet or dry. Summary of the Invention [Problem to be solved by the invention]

[0003] Thus, the interaction between the personal care device and the skin may depend on the condition of the skin. For example, radiofrequency energy may be used to provide a warming experience to the skin during use of the personal care device, such as during shaving. The level of radiofrequency energy delivered to the skin depends on various factors, including factors related to the condition of the skin, which may need to be taken into consideration when determining the settings for radiofrequency energy generation to maintain the safety of the subject to whom the personal care device is applied.

[0004] The present invention aims to address the issues of safety and efficacy of treatments related to wet and dry skin conditions. [Means for solving the problem]

[0005] The moisture level of a subject's skin can affect parameters related to skin surface friction, optical coupling efficiency, electrical contact, and effective impedance. It is an object of the invention described herein to provide an manner in which the moisture level in a subject's skin can be determined, so that interactions between a personal care device, such as a skin treatment device, and the subject's skin can be adjusted based on the moisture of the skin and take into account parameters related to the skin.

[0006] According to a first specific aspect, a personal care device is provided that includes a device for determining a moisture level in a subject's skin. The device for determining a moisture level includes a first electrode configured to contact the subject's skin, a second electrode configured to contact the subject's skin, and a high-frequency RF generator unit configured to supply an RF voltage between the first and second electrodes at each of a plurality of different frequencies such that a current flows from the first electrode through the subject's skin to the second electrode. The device for determining a moisture level further includes a skin impedance measurement unit configured to measure the impedance of the skin between the first and second electrodes at each of the plurality of different frequencies, and a processing unit in operative communication with the RF generator unit and the skin impedance measurement unit. The processing unit is configured to determine the moisture level of the skin based on a slope of a difference in the impedance of the skin at each of the plurality of different frequencies, and to generate a control signal for controlling an operating parameter of the personal care device based on the moisture level of the skin.

[0007] The personal care device may comprise a motor, and the operating parameters generated by the processing unit comprise parameters of the motor.

[0008] Alternatively or additionally, the personal care device comprises an IR light source configured to heat the skin of the subject, and the operating parameters generated by the processing unit comprise parameters related to the IR light intensity of the IR light source.

[0009] In some embodiments, the personal care device comprises a display element, and the operating parameters generated by the processing unit comprise parameters of the display element.

[0010] In some embodiments, the instruction signal comprises a signal for adjusting an RF voltage supplied between the first electrode and the second electrode.

[0011] In some embodiments, each of the plurality of different frequencies is within a frequency range of 0.5 MHz to 100 MHz.

[0012] In a preferred embodiment, each of the plurality of different frequencies is within a frequency range of 1 MHz to 10 MHz.

[0013] In some embodiments, the RF voltage has a value in the range of 5V to 30V.

[0014] According to a second aspect, there is provided a computer-implemented method for generating a control signal for controlling a motor or an IR light source of a personal care device based on determining a moisture level in a subject's skin, the method comprising: activating a high frequency RF generator to generate RF voltages at each of a plurality of different frequencies supplied between a first electrode and a second electrode, wherein when the first and second electrodes are in contact with the skin, current flows from the first electrode through the subject's skin to the second electrode; determining an impedance of the skin between the first electrode and the second electrode at each of a plurality of different frequencies; generating a skin moisture level based on a slope of the difference in skin impedance at each of a plurality of different frequencies; and generating a control signal for controlling an operating parameter of the personal care device based on the moisture level of the skin.

[0015] The operating parameters may include parameters of a motor of the personal care device.

[0016] Alternatively or additionally, the operating parameters may comprise parameters relating to the IR light intensity of an IR light source of the personal care device, the IR light source being configured to heat the subject's skin for the device to determine the moisture level in the subject's skin.

[0017] These and other aspects will be apparent from and elucidated with reference to the embodiments described hereinafter. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic diagram of an example of a device for determining moisture levels in a subject's skin. [Figure 2] FIG. 1 is a schematic diagram of an example of an electrode arrangement. [Figure 3] 1 is a plot showing an example of how impedance varies with frequency for dry and wet skin. [Figure 4] 10 is a plot showing further examples of how impedance varies with frequency for dry and wet skin. [Figure 5] 1 is a schematic diagram of an example of a personal care device. [Figure 6] 10A-10C are schematic diagrams of further examples of electrode placement. [Figure 7] 1 is a flowchart of an example of a method for determining moisture levels in the skin of a subject. DETAILED DESCRIPTION OF THE INVENTION

[0019] Exemplary embodiments will now be described, by way of example only, with reference to the following drawings, in which:

[0020] The moisture level of a subject's skin may change over time, may be different for different areas of the subject's skin, and may differ from the moisture level of another subject's skin. Determining the moisture level of a subject's skin is useful for several reasons, such as setting operating parameters of a personal care device based on the determined skin moisture level. In particular, a priori knowledge of a subject's skin moisture level is important in controlling operating parameters of a device, such as a personal care device, to maintain the safety of the subject to which the device is applied. For example, radiofrequency energy can be applied to a subject's skin to provide a thermal effect within the skin. However, operating parameters related to the generation of radiofrequency energy may need to be set or adjusted based on the skin moisture level to avoid the potential formation of hot spots and / or burns.

[0021] Electrical properties associated with a subject's skin can vary significantly depending on the skin's condition, such as whether the skin is wet or dry, and thus measurements of the electrical properties associated with the skin can be used to determine the skin's moisture level. For example, skin has a relatively low electrical impedance, while dry skin has a relatively high electrical impedance. Electrical impedance can vary for different areas of the skin on the body (e.g., face, hand, etc.) and for different people and skin anatomy. However, measuring electrical impedance may not be a reliable and reliable measure of skin moisture due to factors that affect skin moisture, as discussed above. Therefore, it is an object of the present invention to provide a robust and reliable manner in which the moisture level of a subject's skin can be determined based on the skin's electrical properties. More specifically, a further object of the present invention is to provide operating parameters for an RF generator unit in a personal care device such that RF energy is delivered in a safe manner (e.g., providing a comfortable thermal experience to the subject to which the personal care device is applied, preventing the occurrence of hot spots and / or burns, etc.).

[0022] According to a first aspect, the present invention provides a personal care device 500 including a device 100 for determining a moisture level in a subject's skin. FIG. 1 shows an example of such a device 100 included in the personal care device 500. The device 100 includes a first electrode 102 configured to contact the subject's skin and a second electrode 104 configured to contact the subject's skin. The electrodes 102, 104 may be referred to as probe, sensing, or RF skin-contact electrodes. In some examples, the first electrode 102 and the second electrode 104 may be connected (e.g., electrically connected). The first electrode 102 and the second electrode 104 may be connected (e.g., connected via a radio frequency generator unit (described below)). In some examples, the device 100 includes three or more electrodes. For example, the device 100 may include a first electrode 102, a second electrode 104, and a third electrode (not shown in FIG. 1). The third electrode may be a grounded electrode and / or may be located between the first electrode 102 and the second electrode 104. FIG. 2 shows an example of a schematic diagram of an RF electrode configuration having a first electrode 102, a second electrode 104, and a third electrode 202. The first electrode 102 may be connected to the third electrode 202, and / or the second electrode 104 may be connected to the third electrode 202. In some examples, the first electrode 102 can be connected to the second electrode 104, the first electrode 102 can be connected to the third electrode 202, and / or the second electrode 104 can be connected to the third electrode 202. The electrodes can have the same or different dimensions. For example, the first electrode 104 and the second electrode can each have dimensions of 25 mm x 4 mm, and the third electrode 202 can have dimensions of 25 mm x 5 mm. The electrodes can be spaced apart by the same or different amounts. For example, the first electrode 102 can be spaced 4 mm from the third electrode 202, and the second electrode 104 can be spaced 4 mm from the third electrode 202. In some examples, the dimensions (e.g., width) or shortest side of the electrodes can have a value in the range of 0.1 mm to 10 mm. In some examples, the electrodes have a rectangular, square, circular, etc.

[0023] The device 100 further includes a high-frequency RF generator unit 106 configured to supply RF voltages between the first electrode 102 and the second electrode 104 at each of a plurality of different frequencies, thereby allowing current to flow from the first electrode through the subject's skin to the second electrode. The RF generator unit 106 may include an RF energy source configured to generate RF energy. The RF generator unit 106 may be referred to as a probe RF generator unit for supplying probe RF energy to the probe RF electrode. In other words, the RF generator unit 106 can generate RF energy to be supplied to the subject's skin via the first electrode 102 and the second electrode 104 to raise the temperature of the subject's skin by, for example, approximately 1 to 4°C. The RF voltage can have a voltage range of 5V to 30V, 0V to 30V, 5V to 50V, etc. The voltage signal can have a frequency range of 0.5MHz to 100MHz, 1MHz to 10MHz, etc. In other words, the multiple different frequencies can have frequencies in a range of 0.5 MHz to 100 MHz, 1 MHz to 10 MHz, etc. In some examples, the RF generator unit 106 can be configured to supply RF voltage between the first electrode 102 and the second electrode 104 in a pulsed manner, e.g., with each pulse having a pulse duration in a range of 10 ms to 100 ms. The multiple different frequencies refers to two or more different frequencies (e.g., 10 MHz and 50 MHz). In some examples, when using relatively small electrodes (e.g., <1 mm), a relatively high voltage can be applied to the electrodes.

[0024] In other words, the RF generator unit 106 is configured to supply a voltage between the first electrode 102 and the second electrode 104. This results in an electric field being generated or extending between the first electrode 102 and the second electrode 104. When the first electrode 102 and the second electrode 104 are in contact with the subject's skin (e.g., when the device 100 is in use), the skin acts as a capacitor, storing charge due to the polarization of macromolecules (e.g., proteins or cellular elements) in response to the electric field. When the voltage on the electrodes is switched (e.g., from +10V to -10V for the first electrode 102 and from -10V to +10V for the second electrode 104), the polarization changes and charge is released, resulting in a current. This inductive coupling of the skin results in a low impedance for AC RF currents, but a high impedance for DC currents, as the skin acts as an insulator. Furthermore, polarization changes in skin polymers result in dielectric loss and therefore dielectric heating. Therefore, when the voltages on the electrodes are alternated at high frequencies (e.g., radio frequencies), more significant heating may be achieved in the subject's skin.

[0025] Skin moisture may depend on the skin's ability to bind water to its polymers (e.g., the ability to bind water to its keratinized tissue), which may result in changes in the skin's dielectric properties. Furthermore, skin may contain water that is not bound to skin molecules (e.g., bulk water), which may contribute to the skin's ionic conductivity. Therefore, wet skin may be more conductive than dry skin. Such changes in the skin's electrical properties may increase conductive and dielectric heating. Therefore, determining the skin's moisture level is important, for example, in applications that apply RF energy. As a result, localized heating and / or burns of the skin can be avoided. The device 100 further includes a skin impedance measurement unit 108 configured to measure the skin's impedance between the first electrode 102 and the second electrode 104 at each of a plurality of different frequencies. The skin's impedance may depend on the skin's moisture, as described above, and can be determined based on current and voltage measurements. FIG. 3 is a plot illustrating an example of how impedance varies with frequency over the frequency range of 0.001 MHz to 1000 MHz for dry skin (represented by line 300) and moist skin (represented by line 302) when the first electrode 102 and second electrode 104 of the device 100 are placed on a subject's skin. FIG. 4 is a plot illustrating an example of how impedance varies with frequency over the frequency range of 1 MHz to 10 MHz for dry skin (line 300) and moist skin (line 302) using the same data used in FIG. 3. In the example of FIGS. 3 and 4, the resistive behavior of current in the stratum corneum (i.e., the skin surface) dominates at low frequencies (e.g., <0.1 MHz), resulting in a high impedance plateau. In the example of FIGS. 3 and 4, capacitive coupling across the stratum corneum is greatest at high frequencies (e.g., >100 MHz), resulting in a larger current passing toward the dermis, and therefore the resistive behavior of current in the dermis dominates, resulting in a low impedance plateau.In other words, at low frequencies, the stratum corneum has a high impedance (e.g., the surface of the skin is highly resistive to current flow), and as the frequency increases, the impedance decreases (e.g., the surface of the skin becomes less resistant to current flow), with the subsurface region of the skin becoming dominant in terms of resistance. In the example of Figures 3 and 4, capacitive coupling gradually increases at frequencies in the mid-range (e.g., between 0.1 MHz and 100 MHz), which may be referred to as the transition region. When the skin is wet, it becomes hydrated, which results in higher capacitive coupling, which may in turn shift the transition from high impedance to low impedance toward lower frequencies. Thus, in this example, frequencies in the 1 MHz to 10 MHz range may approach a flat plateau of low impedance, with impedance appearing relatively constant in this frequency range under wet conditions.

[0026] The device 100 further comprises a processing unit 110 in operative communication with the RF generator unit 106 and the skin impedance measurement unit 108. The processing unit 110 is configured to determine the moisture level of the skin based on the slope of the difference in the impedance of the skin at each of a plurality of different frequencies. For example, the slope of the difference in the impedance of the skin at each of two different frequencies can be calculated using the formula TIFF2025535876000002.tif17156, where TIFF2025535876000003.tif2098 is frequency is the skin impedance in TIFF2025535876000004.tif17154, TIFF2025535876000005.tif17154 is frequency TIFF2025535876000006.tif15120 is the impedance of the skin. In other words, the slope of the impedance as a function of frequency is determined. The slope or gradient of the impedance with respect to frequency can be determined using a gradient fitting algorithm, such as a least-squares fitting routine. In some examples, the skin is classified based on Table 1. TIFF2025535876000007.tif58160

[0027] In some examples, device 100 may include memory for storing impedance data, skin moisture data, etc. Device 100 may include a transmitter configured to transmit data (e.g., impedance data, skin moisture data, etc.) to memory external to the device (e.g., a server located in the cloud, etc.). In some examples, a processor located external to device 100 (e.g., an external processor, a processor located in the cloud, etc.) may be configured to determine the moisture level of the skin based on the slope of the difference in skin impedance at each of a plurality of different frequencies. A processor located external to device 100 can be configured to receive data from a transmitter associated with device 100, memory external to device 100, etc.

[0028] RF energy applied to a subject's skin can result in a small amount of heating in the subject's skin. However, the operating parameters of the device 100 (e.g., voltage applied to the electrodes, duration for which RF energy is applied to the subject's skin, etc.) can be set to avoid hot spots and / or burns on the skin. For example, applying RF energy to the subject's skin for 1 second may be sufficient to obtain sufficient data (e.g., impedance data). As a result, the moisture level of the subject's skin can be determined while avoiding excessive heat generation in the skin. It may be beneficial to strike a balance between minimizing the skin heating effect of the applied RF energy and maximizing current flow to minimize calculation errors. In situations where skin impedance is high, such as when using very small electrodes (e.g., electrodes with a width of less than 1 mm), a higher voltage may be preferred. In such an example, pulses of RF energy with pulse durations ranging from 10 ms to 100 ms may be used to minimize heating. In some examples, each electrode can have a width between 0.1 mm and 10 mm, an RF voltage between 5 V and 30 V, and an RF frequency between 1 MHz and 10 MHz.

[0029] In some embodiments, processing unit 110 may be further configured to generate an instruction signal to provide to a receiving device based on the moisture level of the skin. The receiving device may be a personal care device (e.g., a personal care device having device 100). In some examples, the receiving device may be a device external (e.g., separate) to device 100 (e.g., an interactive mirror, a smartphone, a server, a wearable device, etc.). The instruction signal may include a control signal (e.g., a control signal for controlling an operating parameter of device 100), a signal for causing the display of an element in an interactive mirror, etc.

[0030] In some embodiments, the instruction signal may include a signal to adjust the RF voltage supplied between the first electrode and the second electrode.

[0031] For example, a high frequency (e.g., a high RF frequency) may result in or be associated with a low skin impedance. A low skin impedance may result in a relatively greater heating effect (e.g., RF heating) compared to a low frequency (e.g., because a relatively larger current flows between the electrodes at a relatively high frequency compared to a relatively low frequency). The current flow between the electrodes may depend on the voltage applied to the electrodes (e.g., the current between the electrodes may be greater the greater the voltage or potential difference between the electrodes). To minimize heat generation in the skin, a relatively low voltage (e.g., RF voltage) may be applied to the electrodes for a relatively high frequency. In some examples, increasing the current flow between the electrodes may improve the accuracy of determining the skin impedance between the electrodes. For example, the RF voltage may be increased to increase the current flow, and / or the effective resistance of the system may be reduced, e.g., by using larger electrodes. Increasing the current flow between the electrodes may result in a relatively greater heating effect (e.g., compared to a relatively small current flow between the electrodes). Thus, the voltage applied to the electrodes may depend on the frequency at which the voltage is applied to the electrodes (e.g., the voltage and / or frequency may be selected based on a minimum desired level of accuracy of the impedance). In some examples, a first RF voltage may be supplied between the first electrode 102 and the second electrode 104 at a first frequency, and a second RF voltage may be supplied between the first electrode 102 and the second electrode 104 at a second frequency. For example, the first RF voltage may have a first frequency of 1 MHz at 10 V, and the second RF voltage may have a second frequency of 10 MHz at 5 V.

[0032] 5 illustrates an example of a personal care device 500 including the device 100. The personal care device 500 can include a hair cutting device (e.g., a shaving device, an electric shaver, a beard trimmer, a hair trimmer, etc.), a skin care device (e.g., a skin tightening device, a skin rejuvenation device, a skin cleansing device, etc.), etc. The skin rejuvenation device may include an element configured to deliver or apply radio frequency energy to the skin. In some examples, the skin rejuvenation device can include a microdermabrasion device, etc. The skin cleansing device can include a mechanical rotating brush.

[0033] The processing unit 110 is configured to generate a control signal for controlling the operating parameters of the personal care device based on the moisture level of the skin.

[0034] In some embodiments, the operating parameters may include operating parameters of the RF generator unit 106 (e.g., the voltage supplied between the first electrode 102 and the second electrode 104, the duration (e.g., 1 second) for which the AC voltage is applied to the electrodes, etc.). Adjusting the operating parameters of the RF generator unit based on the determined moisture level of the skin can result in adjustments to the level of heat generated in the skin, the skin temperature, the depth of heating within the skin, the rate of skin heating, etc. For example, because wet skin can be associated with a lower impedance, a lower voltage or lower potential difference can be supplied between the electrodes for relatively wet or moist skin so that RF heating is more efficient. Accordingly, the operating parameters of the RF generator unit 106 can be adjusted for safety reasons.

[0035] In some embodiments, the personal care device may include a motor. The operating parameters may include parameters of the motor (e.g., the speed of the motor, the current supplied to the motor, the voltage supplied to the motor, etc.). Skin moisture can affect friction on the skin surface. As a result, it may be desirable to modify the operating parameters of the motor of the personal care device (e.g., the speed of a cutting element of a hair-cutting device). In some instances, a lower motor current for the cutting element of a hair-cutting device may be needed or desired because wet hair is softer and easier to cut. Skin moisture can indicate how wet the hair is, and the motor current can be adjusted accordingly based on the skin moisture.

[0036] In some embodiments, the personal care device may include an infrared (IR) light source configured to heat the subject's skin. The operating parameters may include parameters related to the IR light intensity of the IR light source. Skin moisture may affect the light coupling efficiency of light (e.g., IR light) to the skin, the light transmittance level between the light source and the skin, the light scattering level between the light source and the skin, etc. The IR light may be used to provide a skin warming effect. Relatively moist or hydrated skin may be associated with better light coupling efficiency. Therefore, for safety reasons, a lower light intensity may be used on relatively wet skin.

[0037] In some embodiments, the personal care device can include a display element. The operating parameters can include parameters of the display element. For example, the display element can include a light on the personal care device that indicates whether the device is safe to use. For example, a red light indicates that the device is unsafe to use (e.g., there is a risk of burns), and a green light indicates that the device is safe to use.

[0038] In some examples, the personal care device 500 comprises a hair cutting device (e.g., an electric beard trimmer) that includes a bidirectional beard trimmer unit attached to a handheld housing unit and an RF delivery comb attachment including bidirectional guide comb tines and an RF electrode. An RF generator unit 106 is attached to the handheld housing unit. In use, the RF generator unit 106 can provide RF energy to the skin via the RF electrodes (e.g., the first electrode 102 and the second electrode 104) at two different RF frequencies (e.g., 1 MHz and 5 MHz) at which impedance is measured and recorded. After a predetermined probing time (e.g., 1 second for each frequency), the recorded impedance data is used to determine the slope or gradient of impedance versus frequency. If the slope is approximately TIFF2025535876000008.tif15166 (e.g., TIFF2025535876000009.tif15124~ TIFF2025535876000010.tif15132, the condition can be considered dry. The condition can be considered wet if the electrode has a size of TIFF2025535876000011.tif14134. Figure 6 is a schematic diagram of a further example of an electrode arrangement. A hair cutting device can have an electrode arrangement as shown in Figure 6.

[0039] 7 is a flowchart of an example computer-implemented method 700 for determining moisture levels in a subject's skin. In some examples, a processor may be configured to perform one or more steps of method 700. Method 700 includes, at step 702, activating a high-frequency RF generator to generate RF voltages at each of a plurality of different frequencies supplied between a first electrode and a second electrode such that, when the first electrode and the second electrode are in contact with the skin, a current can flow from the first electrode through the subject's skin to the second electrode.

[0040] The method 700 includes, at step 704, determining the impedance of the skin between the first electrode and the second electrode at each of a plurality of different frequencies.

[0041] The method 700 includes, at step 706, generating a skin moisture level based on the slope of the difference in skin impedance at each of a plurality of different frequencies.

[0042] In some embodiments, the method 700 may include generating an indicator signal for delivery to a receiving device based on the moisture level of the skin.

[0043] In some embodiments, the instruction signal may include a signal to adjust the RF voltage supplied between the first electrode and the second electrode.

[0044] Variations to the disclosed embodiments can be understood and implemented by those skilled in the art practicing the principles and techniques described herein, from a study of the figures, the disclosure, and the appended claims. In the claims, the word "comprise" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in a claim. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage. A computer program can be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless communication systems. Any reference signs in the claims should not be interpreted as limiting the scope of the invention.

Claims

1. 1. A personal care device comprising a device for determining moisture levels in a subject's skin, a first electrode in contact with the subject's skin; a second electrode in contact with the subject's skin; and a high frequency RF generator unit that supplies RF voltages between the first electrode and the second electrode at each of a plurality of different frequencies so that current flows from the first electrode through the subject's skin to the second electrode; a skin impedance measuring unit that measures the impedance of the skin between the first electrode and the second electrode at each of the plurality of different frequencies; a processing unit in operative communication with the RF generator unit and the skin impedance measurement unit, the processing unit configured to determine a moisture level of the skin based on a slope of a difference in impedance of the skin at each of the plurality of different frequencies; the processing unit further generates a control signal for controlling an operating parameter of the personal care device based on the moisture level of the skin; the personal care device further comprises a motor and the operating parameters comprise parameters of the motor; or The personal care device further comprises an IR light source for heating the subject's skin, and the operating parameters further comprise a parameter related to an IR light intensity of the IR light source.

2. The personal care device of claim 1 , wherein the personal care device further comprises a display element, and the operating parameters comprise parameters of the display element.

3. 3. The personal care device of claim 2, wherein the instruction signal comprises a signal to adjust an RF voltage supplied between the first electrode and the second electrode.

4. A personal care device according to any preceding claim, wherein each of the plurality of different frequencies is in the frequency range of 0.5 MHz to 100 MHz.

5. A personal care device according to any preceding claim, wherein each of the plurality of different frequencies is in the frequency range of 1 MHz to 10 MHz.

6. 6. A personal care device according to any preceding claim, wherein the RF voltage has a value in the range of 5V to 30V.

7. 1. A computer-implemented method for generating a control signal for controlling a motor or an IR light source of a personal care device based on determining a moisture level in a subject's skin, the method comprising: activating a high frequency RF generator to generate RF voltages at each of a plurality of different frequencies supplied between a first electrode and a second electrode, wherein when the first electrode and the second electrode are in contact with skin, a current flows from the first electrode through the subject's skin to the second electrode; determining an impedance of the skin between the first electrode and the second electrode at each of the plurality of different frequencies; generating a moisture level of the skin based on a gradient of the difference in impedance of the skin at each of the plurality of different frequencies; generating a control signal for controlling an operating parameter of the personal care device based on the moisture level of the skin; the operating parameters include parameters of a motor of the personal care device; or The computer-implemented method, wherein the operating parameters include a parameter related to an IR light intensity of an IR light source of the personal care device, the IR light source heating the subject's skin.

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