Melasma can occur in many different layers of the skin. Most of the time the melasma is located in the epidermis which is the layer above the bottom layer of skin cells where the stem cells reside. There are times when the pigmentation gets deposited into the dermal layers, or the layers beneath the stem cells. Peels differ in the level that they penetrate. 10-20% tricholoroacetic acid peels (TCA) usually stay in the epidermis but if applied more times can go beneath the stem cell layer. 20-35% TCA peels tend to go a little deeper and can go below the stem cell layer and get some of the deeper pigmentation.
One thing to remember is that the deeper you go the more time it takes to heal and the more risk. 10-20% TCA peels take 3-5 days to peel and heal. Where as 20-35% will take from 4-7 days or more to heal and peel. A woodslamp can help determine the depth of the pigmentation: contrast in epidermal pigmentation is increased while contrast in dermal pigmentation is decreased under Wood's lamp illumination compared to ambient visible light.
