May be caused by deficient or excess pigment, but the term also includes localized conditions. There are various diseases with pigment disorders as a symptom, such as hereditary conditions (including albinism and phenylketonuria). Infections such as leprosy can also cause such disorders; here pigment loss is related to nerve failure. Fungal infections such as pityriasis versicolor or overexposure to radiation can also cause a pale patch, possibly a form of skin cancer. A local pigment excess may be a birthmark or naevus. Excess pigment can occur in pregnancy (chloasma) or be caused by a melanoma. Even when the underlying condition is treated, pigmentation may well not return to normal; redistribution of pigment is a lengthy process. If a patch is not too dark it can be disguised with cosmetics.