How do the green colour changing makeup work?

Question

makeup with those descriptions of “changes with the pH of your skin” or the green ones like the recent one from K*lie Cosmetics (not that other brands has never done it before))

In: 0

Answer 1

I’m not familiar with this makeup in particular, but many, many organic pigments change color in response to a pH change.

On such dyes, there’s either an acidic site that can be deprotonated, or a basic site that can pick up a proton in response to pH change. Either operation can change the length of the “chromophore” of the dye molecule (a series of conjugated double bonds that absorb energy in the visible light region). Changing the conjugation length of the chromophore changes the specific range of light absorbed by the dye, resulting in the observed color change.