Leucism is a partial loss of pigmentation seen in animals which results in white or pale skin, feathers, hair, scales or cuticles. It can also cause patchy colouration. But the eyes are not affected in this condition. Leucism is different from albinism in that it is caused by a decrease in various types of pigments and not only melanin. It is caused because of defects in the differentiation of pigment cells and/or migration from neural crest to feathers, hair or skin during development. If all the pigment cells fail to develop, the entire surface lacks cells capable of making pigment. If only a subset of cells are defective, then it results in patchy colouration. Leucism is sometimes spelled leukism.