It can take minutes to more than 24 hours for the rash to clear once out of the sun.
This article explains solar urticaria symptoms, causes, diagnosis, and treatment.
Solar urticaria is a rare type of photosensitivity rash. It develops on sun-exposed areas and can occur on areas covered by clothing. It typically presents around age 35 but has been seen in infants and older adults. It is more common in females and is seen on all skin types and ethnicities.
“Urticaria” refers to hives, raised bumps or wheals that itch. They can be pinkish-red patches and usually turn white when you press on them. On darker pigmented skin, the raised area is usually skin-colored.
Solar urticaria typically begins within minutes of sun exposure. In 75% of cases, the rash will resolve within an hour of stopping sun exposure. The rest typically go away within 24 hours.
However, the duration of the rash can vary with the intensity of the exposure. A more intense exposure can also cause a more severe rash. Duration and severity can also vary from person to person.
While the exact cause of the rash is unclear, it is likely an immediate allergic reaction involving the release of histamine. The reaction is chronic but may come and go throughout the years. It is thought that something triggers an autoimmune reaction to the skin when exposed to the sun.
A rash with hives is the primary symptom of solar urticaria. It typically starts with an itching or burning sensation within a few minutes of sun exposure. Redness and wheals appear shortly after.
The amount or intensity of the exposure can affect the severity of the rash. Often, the rash is less severe on the face and back of the hands. It may be that these areas have developed a tolerance to the sun. Areas that usually do not get sun exposure, such as the stomach, may react more strongly.
Other symptoms can occur, but this varies from person to person. It is more likely with prolonged sun exposure or when it involves large areas. Other possible symptoms include:
Anaphylaxis — including swelling inside the mouth, tongue, and lips — is possible but rare with solar urticaria.
Solar urticaria is a rash with hives. Hives are itchy, raised bumps, welts, or wheals. They are often red but can also be the same color as the skin, particularly in darker pigmented skin. When you press on hives, they usually blanch, or lose color, in the center.
The wheals have clear edges. However, they can change shape or grow and run together, forming large elevated areas. They can also appear and disappear quickly.
Solar urticaria is an idiopathic condition — there is no known cause for it. The most likely explanation is that it is an immediate allergic reaction.
Experts believe sunlight activates some component in the skin that acts as an allergen. Antibodies to the allergen stimulate mast cells. These immune cells release substances, such as histamine, that cause allergic reactions.
The wavelengths of light that can trigger solar urticaria include ultraviolet (UV)-A, UV-B, and visible light. The type of light that causes the reaction can vary from person to person.
Solar urticaria can affect all skin types and people of ages. However, it most commonly develops in young adults. The median age of onset is 35 years. Solar urticaria is more common in females.
To diagnose solar urticaria, doctors rely on your description of the problem — experiencing hives within a few minutes of sun exposure. Without sun exposure, a physical exam would be standard.
There are other conditions doctors need to rule out, including:
- drug reactions, including medications that can cause photosensitivity
- allergic reactions to sunscreen or fragrance
- systemic lupus erythematosus
- polymorphous light eruption
Phototesting can help confirm a solar urticaria diagnosis. This involves exposing the skin to UV-A, UV-B, and visible light. It can give you information about the most triggering wavelengths and how long your skin can tolerate exposure.
A skin biopsy can be helpful in some cases.
Treating solar urticaria usually involves a combination of approaches. Doctors may recommend the following step therapy:
- sun protection with broad-spectrum sunscreen, protective clothing, and sun avoidance
- nonsedating antihistamines, such as cetirizine (Zyrtec) or loratadine (Claritin), at higher-than-normal doses
- phototherapy, which involves exposing the skin to light in gradual doses to build a tolerance or hardening
- omalizumab (Xolair), which is an antibody drug with an indication for treating chronic urticaria — a similar condition
Other options for resistant cases include:
- intravenous immunoglobulins
- medications, including cyclosporine (Gengraf, Neoral, Sandimmune) and afamelanotide (Scenesse)
- plasma exchange
Sun protection is the mainstay of preventing a solar urticaria flare. This includes:
- avoiding sun exposure as much as possible
- seeking shade whenever possible
- using a broad-spectrum sunscreen with UV-A and UV-B coverage every day
- wearing sun protection factor (SPF) clothing or clothes that cover and shield the skin, including wide-brimmed hats
Here are some other questions people often ask about solar urticaria.
How common is solar urticaria?
Solar urticaria is not common. It accounts for less than 1% of cases of urticaria.
What’s the difference between solar urticaria and polymorphous light eruption?
Polymorphous light eruption (PMLE) is another type of photosensitivity. In fact, it is the most common form. However, PMLE is a delayed allergic reaction to sun exposure.
The rash it causes can take several forms, hence the term “polymorphous.” PMLE is also seasonal. It tends to begin in the spring or early summer. It may improve throughout the summer and go away during the fall and winter.
Solar urticaria is a rash with hives that appears within minutes of sun exposure. It is a chronic condition. However, the duration of the rash and its severity can vary from person to person. These factors also vary with the amount and intensity of sun exposure.
Prevention relies on sun protection and avoiding exposure. Many people with solar urticaria end up staying indoors to avoid reactions. This can lead to poor quality of life.
