The darkening of the skin at the back of the neck may be caused by physiological factors such as ultraviolet radiation, or it may be caused by diseases such as acanthosis nigricans, post-inflammatory hyperpigmentation, etc. It can be improved by general treatment and medication. 1. Physiological factors: the darkening of the skin at the back of the neck may be caused by ultraviolet radiation from the sun, and it is necessary to wear sunscreen and play sunscreen to cover up the sun when you go out. You can also use hydroquinone cream externally to inhibit melanin production. 2. Acanthosis nigricans: If the darkening of the skin at the back of the neck is caused by acanthosis nigricans, you need to control your diet and exercise moderately. Patients can follow the doctor’s instructions to use topical carbotriol, tacalcitol and other drugs, with the role of regulating keratin. You can also use topical retinoic acid ointment, which can reduce hyperpigmentation. 3. Post-inflammatory hyperpigmentation: If the back side of the neck is dark due to post-inflammatory hyperpigmentation, you need to pay attention to sun protection. Patients can follow the doctor’s instructions to use niacinamide, azelaic acid and other ointments, can inhibit the proliferation of melanocytes. You can also use topical retinoic acid ointment, adapalene gel and other retinoic acid ointment, which can promote epidermal cell renewal, but there is a risk of teratogenicity. There are many reasons for the darkening of the skin on the back side of the neck, and after ruling out physiological factors, patients are advised to go to the hospital to clarify the cause of the disease and then treat it.