Erythema on the back of the neck is considered to be the cause of contact dermatitis, folliculitis, and solar dermatitis, which can be treated by applying medication as well as taking oral medication. 1. Contact dermatitis: it is usually caused by skin contact with some or several irritating substances. The lesions are confined to the area of contact and are characterized by well-defined erythema, papules and small blisters. It is necessary to immediately detach from the sensitizer, wash the skin, and take oral antihistamine drugs such as loratadine. 2. Folliculitis: Folliculitis is also an inflammatory skin disease, in the early stages of the disease will lead to erythema on the back of the neck, with the further aggravation of the disease, there will be pustules, accompanied by itching and pain. You can apply antibiotics such as mupirocin and erythromycin ointment for treatment. 3. Solar dermatitis: solar dermatitis and long-term exposure to ultraviolet radiation, the disease will lead to red, swollen skin, burning, pain, after the disease is serious, it will lead to a large number of skin flaking, resulting in the back of the neck long red spots. You can apply glycerite lotion for treatment. Erythema on the back of the neck may have other reasons, the patient needs to go to a professional dermatologist, and then choose the appropriate way of treatment, not to use drugs blindly.