A red patch on the back of the neck can be caused by contact dermatitis, eczema, infection, trauma and other reasons. 1. Contact dermatitis: Allergic or irritant reactions occurring after contact with certain sensitizing or irritating substances in the area can also cause a red patch on the back of the neck. 2. Eczema: Inflammatory skin reactions caused by internal and external stimuli can also cause redness, rashes and itching, which may also lead to a reddish color on the back of the neck. 3. Infections: for example, folliculitis, boils and carbuncles caused by bacterial infections; herpes caused by viral infections; ringworm caused by fungal infections. This may lead to a reddish color on the back of the neck. 4. Trauma: The skin on the back of the neck can also become red when it is squeezed or bruised. There may be other reasons for the redness on the back of the neck, so it is recommended to go to the hospital in time for examination, to clarify the cause of the disease, and to follow the doctor’s instructions for treatment.