Endocrine disorders may cause darkening of the skin of the neck. Darkening of the skin is mainly due to the high level of melanin in the skin, and endocrine regulation of melanin metabolism plays a very important role. When there is an endocrine imbalance in the body, if there is an increase in the secretion of hormones such as melanocyte stimulating hormone (MSH), adrenocorticotropic hormone and oestrogen, melanin can be increased, resulting in a darker neck.