The face will be red when it is hot and exposed to the sun, considering solar dermatitis, cholinergic urticaria, prickly heat and so on. 1. Solar dermatitis: solar dermatitis is related to receiving strong light exposure, there will be acute damage, mainly manifested as redness, swelling, burning, pain, and in severe cases, there will be blisters, burning, skin flaking and other symptoms. 2. Cholinergic urticaria: cholinergic urticaria is the skin local center after the rise in body temperature, prompting cholinergic nerve impulses, the release of acetylcholine, the role of the mast cell symptoms, mainly in the form of rounded pimples, surrounded by a red halo. 3. prickly heat: If it happens in the hot summer, it may also be prickly heat, which is a common skin disease in the hot and humid environment and the small sweat gland ducts are blocked with the relationship between the main manifestations of the skin appeared in small blisters, papules or mounds of herpes, there will be tingling and itching. The face is hot and sunny on the red there may be other reasons (such as excessive cleaning or abuse of hormones caused by skin barrier damage), it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, to give targeted treatment or treatment, do not self-medication.