Photodermatitis

What is photodermatitis?

Photodermatitis is a medical term for skin conditions that are triggered by sensitivity to sunlight, which is also known as photosensitivity. It’s often referred to as a sun allergy.

There are several varieties of photodermatitis, with different causes. This means the severity of your symptoms can vary depending on the type you’re affected by. Most often though, photodermatitis has an eczema-like effect on the skin.^[1]

It can be caused by hypersensitivity (an exaggerated immune response) to sunlight, but it can also be triggered by drugs or chemicals that make your skin react to exposure. These are known as photosensitisers. Sunlight exposure can also exacerbate underlying skin conditions and cause symptoms to flare up.

Who gets photodermatitis?

Photodermatitis can affect men and women of all ages. People can be more prone to it at different stages of life, and it can also be affected by genes and environmental factors.^[1]

Those with very light skin who are prone to burning easily in the sun are often thought to be photosensitive, compared to people with fair skin. The most likely group to be affected by photosensitivity is thought to be anyone with Fitzpatrick skin type 1.

The Fitzpatrick scale was created in 1972 by Thomas B. Fitzpatrick to measure individuals’ likeliness to tan or burn when they spend time in the sun. Those with lower skin types on the scale are more likely to be photosensitive.

How common is photodermatitis?

Because photodermatitis has several causes, it’s difficult to say just how many people are affected by it. It can be triggered by lots of medications, such as NSAIDs, so potentially anyone using them could find they become sensitive to sunlight.

Light-skinned people, especially those who have red hair and blue eyes, are thought to be more prone to photosensitivity^[2], and so they might be more likely to develop skin rashes when spending time in the sun.

What causes photodermatitis?

All forms of photodermatitis are caused by sensitivity to sunlight. Specifically, ultraviolet radiation (UVR) provokes an allergic reaction in the skin of people who are exposed to the sun. This can be a natural immune response for people with a sun allergy (hypersensitivity), or can be caused by medications that make people react abnormally, such as sunscreens and some antibiotics.

There are three types of UV rays: ultraviolet A (UVA), ultraviolet B (UVB), and ultraviolet C (UVC). People with photodermatitis can either react to one type of UVR, or several.

What are the symptoms of photodermatitis?

Photodermatitis usually appears as an eczema-like rash, but your symptoms may differ depending on what’s causing them.

• Polymorphic light eruption is a common type of skin rash that develops from both sun exposure and artificial UV rays, such as those used on sunbeds. This causes pink or red spots to form on any skin that’s been exposed to the sun.^[1]
• Actinic prurigo is another form of photodermatitis, and it’s usually worse during the summer months. It causes a rash that is made up of spots and blisters that can sometimes develop into scabs.
• Solar urticaria is a type of sun allergy that tends to affect young women. It’s a rare type of photodermatitis, which causes hives (itchy bumps) to appear on sun-exposed skin, sometimes within minutes.^[2]

The rash is more likely to affect the areas of your skin that have been exposed to sunlight, such as the neck, face and hands, than those that are covered up.

Can photodermatitis lead to other problems?

Photodermatitis isn’t likely to lead to anything more serious, but getting the right treatment for it can help to reduce the chances of it getting worse.

Eczema-like rashes can leave your skin feeling sore and irritated, and without proper help you might struggle to stay on top of your flare-ups. The condition can also impact your behaviour, as knowing you’re sensitive to UVR might make you avoid sunlight altogether. A 2020 study found that people with a sun allergy are more likely to develop vitamin D deficiency^[3]. Low vitamin D levels can contribute to osteomalacia (bone softening), muscle weakness, and depression.^[4]