Melanosis on the neck may be related to physiological factors such as friction, followed by diseases such as acanthosis nigricans and post-inflammatory hyperpigmentation. 1. Physiological factors: long-term friction on the neck may lead to melanosis on the neck. 2. Acanthosis nigricans: the cause of acanthosis nigricans is unknown and may be caused by genetic defects, diabetes, and obesity. The patient’s skin will have the symptom of deepening color, mostly gray, brownish yellow, black, etc., and accompanied by itching. 3. Post-inflammatory hyperpigmentation: the cause of the disease is more, may be caused by disease, trauma and environmental factors, the patient’s local skin will appear hyperpigmentation spots, such as light brown, black, blue-black and so on, if the neck skin has suffered from inflammation, then the part may appear melanin pigmentation. The causes of melanosis on the neck are not one and the patient is advised to go to a regular hospital for examination to clarify the cause.