Solar urticaria, also known as sun allergy, is a rare allergy to sunlight that causes hives to form on sun-exposed skin. Itchy, reddish spots or stripes usually appear a few minutes after sun exposure. They can last for a short time or up to hours. The cause of solar urticaria is unknown. The allergy can become chronic, but the symptoms can be treated.
What Are the Symptoms of Sun Allergy?
The main symptoms of sun allergy are reddish patches on your skin that itch, sting, and burn. If the hives cover most of your skin, you may have other common allergy symptoms, such as:
- Difficulty breathing
The rash may be more likely to affect areas of your skin that are not usually exposed to sunlight. You may not experience redness on your hands or face that is frequently exposed to sunlight. If you are very sensitive to the sun, hives may also appear on areas of your skin that are covered with thin clothing. The appearance of the rash may vary depending on individual sensitivity. Sometimes your skin may blister or crust over. When the redness disappears, it leaves no trace.
What Causes Solar Urticaria?
The exact cause of solar urticaria is unknown. It occurs when sunlight activates the release of histamine or a similar chemical in your skin cells. The mechanism is described as an antigen-antibody reaction. This type of reaction occurs when your immune system produces antibodies to counter the certain antigen or irritant that reacts to sunlight. Hives are an inflammatory reaction that occurs.
Your risk of solar urticaria may be increased if:
- Having someone in the family with the condition
- Having dermatitis
- Regular use of perfumes, disinfectants, dyes or other chemicals that can trigger the condition when exposed to sunlight
- Use of antibiotics or other medications, including sulfa drugs, that can trigger the condition
In some cases, certain wavelengths of ultraviolet (UV) light trigger an allergic reaction. Most people with solar urticaria react to UVA or visible light.
What is the Difference Between Sun Allergy and Rash?
A rash occurs when your pores are clogged and sweat accumulates under your clothes. It can happen without exposure to sunlight. E.g; In hot, humid weather, a rash can occur anywhere on your body that sweats, especially in the folds of your skin. Areas that may be more at risk for a rash include:
- Under your breasts
- In the groin
- Under the armpits
- Between your inner thighs
Solar urticaria only occurs as a result of exposure to sunlight. A rash can occur in any season. Babies may experience a rash if they are wrapped in blankets. The rash is usually; Solar urticaria typically lasts only hours, while it disappears on its own within a few days.
How Common Is Sun Allergy?
Solar urticaria is a rare allergy seen all over the world. The median age for a person’s first time is 35, but it can affect you at any age. It can even affect babies. Sun allergy can occur in people of all races, but some forms of the condition may be more common among Caucasians.
How Is Solar Urticaria Diagnosed?
Your doctor can diagnose solar urticaria from a physical exam. They will look at your rash and ask you about its appearance and date of disappearance. Solar urticaria usually appears a few minutes after sun exposure and disappears quickly if you step out of the sun. It leaves no trace.
Your doctor will ask you questions about your history and your reaction to sunlight. Your doctor may also need to do one or more tests to confirm a diagnosis:
- The phototest looks at how your skin responds to UV light from a sun lamp of different wavelengths. The wavelength to which your skin reacts can help identify your particular sun allergy.
- Patch testing involves putting different substances known to trigger allergies on your skin, waiting a day, and then exposing your skin to UV radiation from a sun lamp. If your skin reacts to a certain substance, it may be what triggers solar urticaria.
- Your doctor; Blood tests or skin biopsies may be used if they think your hives are caused by another medical condition, such as lupus or a metabolic disease.
How Is Solar Urticaria Treated?
Sometimes solar urticaria goes away on its own. Treatment for solar urticaria depends on the severity of your symptoms. Staying out of the sun may resolve symptoms if your reaction is mild. In mild cases, your doctor may prescribe oral antihistamines or over-the-counter creams such as aloe vera or calamine lotion to calm the hives.
If your reaction is more severe, your doctor may recommend other medications, such as:
- Hydroxychloroquine, an antimalarial drug
- Montelukast, often used to treat asthma
Montelukast should only be used as an allergy treatment if no suitable alternative is available.
Your doctor may also recommend phototherapy. This treatment will prepare your skin for the summer sun by regularly exposing your skin to ultraviolet radiation from a sun lamp in the spring. This may desensitize you, but the effects may not be long lasting.