Melanin is also important in mammalian pigmentation. This process is less efficient with increased melanin pigmentation in the skin. Light skin pigmentation protects against vitamin D deficiency. Populations with light skin pigmentation evolved in climates of little sunlight. It also lacks any pigmentation in its skin. It was beneficial to them to reduce their skin pigmentation. It can be based on their skin pigmentation, their mucous or their bones. Additional types of nevi do not involve disorders of pigmentation or melanocytes. However, the relationship between skin pigmentation and photoprotection is still uncertain. The Fitzpatrick scale remains a recognized tool for dermatological research into human skin pigmentation. Ocular albinism affects not only eye pigmentation but visual acuity, as well. Fair-skinned women show this phenomenon less often than women with darker pigmentation. Blond hair is the result of having little pigmentation in the hair strand. In crustaceans, there is a second oxidase activity leading to cuticle pigmentation. In humans, the pigmentation of the iris varies from light brown to black.