Possible Involvement of Keratinocyte Growth Factor in the Persistence of Hyperpigmentation in both Human Facial Solar Lentigines and Melasma

Abstract

Acute pigmentation due to tanning is commonly understood as increased melanization of the epidermis observed in the skin after ultraviolet (UV) exposure, and the mechanisms underlying this condition are well understood now. Keratinocyte-derived gene products are upregulated by UV irradiation and act as paracrine factors in the skin to stimulate melanogenesis and melanin transfer by melanocytes 1 . Although acute pigmentation disappears over time, some types of hyperpigmentary disorders such as freckles, solar lentigines, and melasma, tend to persist if patients do not receive any treatments such as topical cosmetic products, medication, or laser. Solar lentigines are dark brown spots that occur on sun-exposed areas 2 , typically on the face, upper back, and