Melasma (also known as chloasma faciei,[1]:854 or the mask of pregnancy  when present in pregnant women) is a tan or dark skin discoloration. Melasma is thought to be caused by sun exposure, genetic predisposition, hormone changes, and skin irritation. Although it can affect anyone, melasma is particularly common in women, especially pregnant women and those who are taking oral or patch contraceptives or hormone replacement therapy (HRT) medications. The symptoms of melasma are dark, irregular well demarcated hyperpigmented macules to patches. These patches often develop gradually over time. Melasma does not cause any other symptoms beyond the cosmetic discoloration.[4] Patches can vary in size from 0.5 cm to larger than 10 cm depending on the person. The location of melasma can be categorized as centrofacial, malar, or mandibular. The most common is centrofacial in which patches appear on the cheeks, nose, upper lip, forehead, and chin. The mandibular category accounts for patches on the bilateral rami, while the malar location accounts for patches only on the nose and checks. There are two different kinds of melasma, epidermal and dermal. Epidermal melasma results from melanin pigment that is elevated in the suprabasal layers of the epidermis. Dermal melasma occurs when the dermal macrophages have an elevated melanin level.[8] Melasma is usually diagnosed visually or with assistance of a Wood's lamp (340 - 400 nm wavelength).[9] Under Wood's lamp, excess melanin in the epidermis can be distinguished from that of the dermis. This is done by looking at how dark the melasma appears, dermal melasma will appear darker than epidermal melasma under the Wood's lamp.