Method for measuring skin erythema

1. A method for measuring skin erythema comprising: a)

acquiring a digital image of skin under orthogonal polarization conditions with a white calibration standard included in the field of view of the image;

b) identifying median intensity values for a red, a green, and a blue channel for the white standard;

c) translating skin reflectance values given by the red, green, and blue intensity values of each pixel of the image to absorbance values by taking the logarithm of a ratio of the white standard values to the skin reflectance values at each of the red green and blue channels separately, where the absorbance equals:

log( I white (red,green,blue)/ I skin (red,green,blue))

 for all pixels representing skin;

d) subtracting the red channel absorbance values from the green channel absorbance values for all pixels representing skin;

e) subtracting the red channel absorbance values from the blue channel absorbance values for all pixels representing skin;

f) calculating a ratio of the value calculated at step (d) to the value calculated at step (e); and

g) building an intensity map of the ratio calculated at step (f).

2. A method of demonstrating the efficacy of a skin care product comprising:

analyzing an area of the skin according to the method of claim 1 ;

applying a skin care product to the same area of skin for an effective amount of time;

making a subsequent analysis of the area of the skin according to the method of claim 1 ; and

comparing the intensity maps of the images to demonstrate a reduction in erythema of the skin.

3. A method of demonstrating the mildness of a skin care product comprising:

analyzing an area of the skin according to the method of claim 1 ;

applying a skin care product to the same area of skin for an effective amount of time;

making a subsequent analysis of the area of the skin according to the method of claim 1 ; and

comparing the intensity maps of the images to demonstrate no increase in erythema of the skin.