Darkening of the neck and armpits may be caused by normal physiological reasons or pathologic factors. Common pathologic factors include: acanthosis nigricans, hypoadrenalism, and so on. 1. Physiological reasons: under normal circumstances, the neck and armpits will be slightly heavier than other parts of the skin pigmentation. Especially for obese people, there are skin folds in the neck and armpits, which are easy to accumulate sweat and dust, so the neck and armpits are darker. If there is no discomfort, there is usually no need for treatment. 2. Acanthosis nigricans: It is a rare skin disease. It often occurs in the folds of the skin such as neck and armpits, and the pigmentation in this area is more serious, which will make the skin dry, rough, and even lesions and itching. 3. Hypoadrenalism: the darkening of the skin caused by it is not only seen in the neck and armpits, but also diffuse darkening of the face, trunk, limbs, etc., and is often accompanied by fatigue, dizziness, and reduced immunity. All in all, for the neck, armpit darkening, if there is no discomfort symptoms can not be treated, if there are other symptoms, it is recommended to go to the hospital in time to clarify the diagnosis and treatment.