Red patches on the back of the neck may be caused by contact dermatitis, eczema, pityriasis rosea, or other diseases such as psoriasis. 1. Contact dermatitis: contact dermatitis is an allergic reaction caused by skin contact with external substances that irritate the skin. Patients mainly manifest erythema, edema, papules, itching, burning, etc., but also fever, fatigue, headache and other symptoms. 2. Eczema: the cause of eczema is not completely clear for the time being, most patients are due to immune dysfunction, systemic diseases, heredity and allergen stimulation and other factors. The main symptoms of patients are edema, erythema, blisters, papules, etc., and there will be erosion, itching, flaking and other symptoms. 3. pityriasis rosea: the cause of pityriasis rosea is not yet clear, it is considered to be caused by viral infection and other factors. Patients will have rose-red spots, itching, blisters, etc. They will also have symptoms such as low-grade fever, headache and sore throat. 4. Other: psoriasis, vascular nevus and other diseases can also lead to the phenomenon of red patches on the back of the neck. Patients with symptoms of red patches on the back of the neck should consult a doctor in a timely manner, follow the doctor’s instructions for treatment, do not self-medication.