A method for testing the effect of a 
skin care product includes measuring a 
mechanical property of 
skin tissue using nonlinear stochastic 
system identification, applying the product to the 
skin, repeating the measurement of the 
mechanical property after the application of the product, and comparing the before and after measurements to quantify the effect of the product.Measuring the 
mechanical property of the skin can include placing a probe against a surface of the skin, perturbing the skin with the probe using a stochastic sequence, and measuring the response of the skin to the perturbation. Perturbing the skin can include indenting the skin with the probe, extending the skin with the probe, and sliding the probe across the 
skin surface. The mechanical property may be indicative of skin compliance, 
skin elasticity, skin stiffness, or skin damping. The mechanical property can be dependent on perturbation depth and may be measured at a plurality of anatomical locations.