Melanin in humans is the primary determinant of skin color. Melanin in skin is produced by melanocytes in the epidermis in response to environmental triggers, such as increased sun exposure, or other physical or chemical perturbation. Melanin is also found in hair, the pigmented tissue underlying the iris of the eye, as well as the stria vascularis of the inner ear.
Environmental and/or physiological stress can cause disorders in melanin production. For example, post-inflammatory hyperpigmentation (“PIH”) represents the sequelae of various cutaneous disorders, including infections, allergic reactions, mechanical injuries, reactions to medications, phototoxic eruptions, trauma (e.g., burns), inflammatory diseases (e.g., lichen planus, lupus erythematosus and atopic dermatitis), as well as reactions to devices, including electromagnetic devices such as ultrasound, radiofrequency, lasers, light-emitting diodes and visible light therapy, as well as microdermabrasion reactions. PIH occurs widely in the human population and can be the source of significant psychosocial distress for those affected with this disorder. PIH is a pathophysiologic response to cutaneous inflammation. Melanocytes can be stimulated by the inflammatory process to synthesize and secrete more melanin from melanocytes, or the number of melanocytes can increase in the epidermis, leading to hyperpigmentation of the skin. PIH can also occur when inflammation disrupts the basal cell layer, causing melanin pigment to be released and subsequently trapped by macrophages in the papillary dermis. Hyperpigmentation or hypermelanosis disorders due to environmental stressors, such as hormonal imbalance, can also affect melanin or pigmentation levels in the skin.