Radiomagnetic emissions from the sun, principally UV light of the A and B spectra, exert a significant influence on skin pigmentation. Polypeptide hormones from the anterior pituitary gland, especially melanocyte-stimulating hormone (MSH), also enhance melanin pigmentation. In women, estrogens stimulate an increase in melanocyte and pigmentary responses in facial, genital, and areolar skin. Chemicals such as theophylline, caffeine, cholera toxin, and prostaglandin E increase the effect of MSH on skin pigmentation. Finally, heat, inflammation, and mechanical injury also stimulate increased pigment formation, especially in the skin of darkly pigmented persons. Based on clinical descriptions of individuals exposed to toxic doses of sulfur mustard, sulfur mustard can also potentiate skin pigmentation. Topical nitrogen mustard, when applied to the skin in the treatment of psoriasis and cutaneous T-cell lymphoma, causes increased skin pigmentation through mechanisms that are as yet unknown.

Injury to the skin of sufficient intensity to cause destruction of melanocytes will result in skin that is devoid of pigmentation. White patches of skin will be noted in even the darkest of pigmented races (leukoderma). Thus, skin that has been subjected to injuries with locally varying intensities, such as after sulfur mustard and Lewisite exposure, will characteristically show areas of depigmentation alternating with areas of hyperpigmentation. In fact, over time the process of healing reveals significant changes in the patterns of pigmentation.

Following skin injury, epithelial cells surrounding the external orifices of the hair follicle and other adnexa proliferate and migrate outward from their source to repopulate skin devoid of epithelium. Epithelial cells from surrounding normal skin also contribute to the process of repair in skin devoid of epithelium. Melanocytes surrounding uninjured hair follicles are stimulated to replicate and increase the production of melanin. Regenerated epithelial cells surrounding the orifices of the hair follicles, then, are the first cells to receive new pigment. The clinical picture of melanocytes repopulating skin is referred to as having a "salt and pepper" appearance. The salt and pepper appearance of skin after sulfur mustard exposure is often written about with some degree of bewilderment. Yet, this is a process that occurs commonly after mechanical and chemical injury to skin.

As melanocytes grow and repopulate normal skin, there is a tendency for overmelanization of any given area. Overmelanized skin at the edges of a healing wound is characteristically darker than skin distal to the healing site. As healing progresses, such skin will eventually return to its normal color and appearance. Normalization of this process often takes 6 to 12 months. The inherent skin color of the affected individual usually determines the amount of time required to return to a normal state.

In many ways, acute and chronic sulfur mustard skin injury mimics