The red spots on the neck may be mosquito bags or other causes, such as folliculitis and contact dermatitis. 1. Mosquito bags: after being bitten by mosquitoes, some toxins will enter the patient’s body, and these toxins will cause skin lesions, erythema of the skin, accompanied by pain and itching. 2. Folliculitis: after the hair follicle is damaged, it will lead to the invasion of pathogenic microorganisms, causing infection and folliculitis, and there will also be erythema, which is more commonly caused by Staphylococcus aureus, and is related to Propionibacterium acnes if it is combined with acne folliculitis. 3. Contact dermatitis: contact dermatitis is the skin contact with certain external substances, causing inflammation of the skin at the contact site, usually occurring in the exposed parts of the body, erythema, edema, papules and other manifestations, but also accompanied by itching symptoms. Erythema on the neck, it is recommended to go to the hospital in a timely manner, to clarify the cause of the disease under the guidance of the doctor to treat the symptoms, can not be blindly diagnosed. Usually pay attention to keep the local cleanliness and hygiene, do not scratch.