Melanin deposits on the neck may be caused by ultraviolet radiation, inflammatory stimulation, lichen planus, acanthosis nigricans and other factors. 1. Ultraviolet radiation: often in the ultraviolet environment, usually do not pay attention to sunscreen, may lead to melanin precipitation. 2. Inflammatory stimulation: Skin infection, mechanical injury, allergy, drug reaction, trauma and other factors lead to inflammatory reactions in the skin. After the inflammation, the pigmentation manifestation appears, resulting in the black color of the neck area. 3. lichen planus: lichen planus is a superficial skin infection caused by Malassezia violating the stratum corneum of the skin, which is mainly manifested as rash, hypopigmentation and deepening of pigmentation. 4. Acanthosis nigricans: the cause of acanthosis nigricans is not yet completely clear, mainly manifested as deepening of skin color, papillary and velvety thickening of the skin surface, which can be seen in the neck, armpits and other parts of the body. Neck with melanin precipitation, it is recommended to do a good job of care of the affected area, do not scratch the stimulation induced infection. If necessary, go to the hospital dermatology department for examination, combined with the doctor’s advice treatment.