What’s the difference between sunburn and sunburn? What is photosensitivity (sunlight allergy)?

Photosensitivity is a skin condition that causes itching, redness, and rashes triggered by exposure to sunlight. It is also called a “sun allergy” because it is believed that the immune system overreacts to sunlight and causes symptoms.

When it comes to skin symptoms caused by sunlight, the first thing that comes to mind is sunburn. Sunburn, in which the skin becomes red, inflamed, or darkened by exposure to ultraviolet rays, can occur to anyone who is exposed to strong sunlight to some extent.

On the other hand, in the case of photosensitivity, symptoms may appear even in doses of ultraviolet rays that would normally not cause a reaction. In addition, symptoms may appear not only from ultraviolet rays but also from visible light contained in sunlight. There are large individual differences in how much sunlight it takes to cause skin symptoms, but in severe cases, there are cases where the skin reacts to sunlight coming in through a window indoors.

Two common types of photosensitivity are solar urticaria and multiform solar rash. The exact cause of these is not known, and it is thought that they are due to the constitution.

• Sunlight urticaria
  A raised rash, redness, and itching occur on areas exposed to sunlight.The symptoms usually appear within a few minutes after exposure to the sun and disappear within a few hours, but the symptoms may persist for a long time.When solar urticaria occurs over a wide area of ​​the body, symptoms other than the skin such as headache, dizziness, nausea, weakness, and wheezing (wheezing and wheezing sounds when breathing) may appear.
• Polymorphic solar
  eruption A red, bumpy rash occurs in sun-exposed areas. Usually, it often develops 30 minutes to several hours after exposure to sunlight, but it may develop after the next day. Symptoms often disappear spontaneously after a few days, but may cause pigmentation if repeated many times.
  In addition, chemical substances such as drugs can become allergens when exposed to sunlight, resulting in photosensitivity.
• Photocontact dermatitis
  Symptoms such as redness and rashes may appear when the area where topical drugs such as patches and ointments are applied is exposed to sunlight.
• Photosensitive drug eruption
  Symptoms such as rashes may appear on the skin exposed to the sun when exposed to the sun after taking certain types of antibacterial drugs, anticancer drugs, antipsychotic drugs, diuretics, etc.

Photosensitivity can also be caused by diseases related to the immune system, such as collagen disease, or genetic diseases.

The symptoms of photosensitivity often disappear on their own within a few days, but if they persist for a long time or if the symptoms recur, we recommend that you see a dermatologist. In addition, since the symptoms appear when exposed to sunlight, the symptoms often appear on the face, which is easily visible because it is not covered by clothing. If you want your symptoms to subside quickly, you may want to see a doctor.

After confirming the symptoms of the skin, if the symptoms appear only in the part exposed to the sun, it can be judged as photosensitivity. Medicines and cosmetics may be the cause, so check if there are any medicines or cosmetics that you have recently started using. If necessary, a “photosensitivity test” is performed to examine the cause in detail by exposing the skin of the back and other areas to various types and amounts of light.

To relieve the symptoms of photosensitivity, symptomatic treatment with drugs is performed. Antihistamines (oral medicines) and topical steroids are commonly prescribed.

To prevent recurrence of photosensitivity, it is important to avoid sunlight as much as possible. Take measures such as using a hat or parasol, and wearing long-sleeved clothing to avoid exposing your skin.

It is also recommended to use sunscreen all year round. The back of the hand is surprisingly easy to forget to apply. In addition, some patients develop symptoms when they change from long sleeves to short sleeves. Be sure to apply evenly over exposed skin, including areas that have not been exposed to the sun before. However, there are some cases where sunscreen ingredients cause rashes and photosensitivity. At night or after returning home, it is important to remove it as soon as possible.

If a chemical is thought to be causing photosensitivity, the offending substance may be stopped. a similar effect. Let’s discuss. However, even after stopping the use of these chemicals, sun exposure may cause symptoms to reappear, so people should avoid sun exposure for about a week after stopping use of these chemicals .

[Profile of Maaya Konishi]

Director of Sugamo Sengoku Dermatology Department
Graduated from Kyorin University School of Medicine in 2003 and entered the Dermatology Department of Tokyo Medical and Dental University. After working in the Department of Dermatology at Tsuchiura Kyodo Hospital, Department of Dermatology at Tokyo Metropolitan Bokuto Hospital, and Department of Dermatology at Kawaguchi Industrial General Hospital, Sugamo Sengoku Dermatology Department opened in 2017. He is a dermatologist certified by the Japanese Dermatological Association.