The truth behind sun allergies: How UV rays and chemicals trigger skin reactions
It’s an immune system response triggered by sunlight…
You can dodge food allergies by steering clear of certain foods, but what about the sun? It’s everywhere, and impossible to escape.
Dubai-based homemaker Sweekriti Panigrahi has learned to navigate this unusual challenge, which affects her mother-in-law, when they go on vacation. As her mother-in-law has an extreme sensitivity to sunlight, Panigrahi explains that she and her husband have now developed a meticulous travel routine. They pore over maps and destination guides to find places where the sun’s intensity is less harsh. Even then, there’s always a slight risk of her mother-in-law falling ill. As a result, it’s common sight to see her wrapped up in hats, scarves, and layers of protection during their travels, accompanied by a well-packed box of medicines and creams. “We just do our best to minimise her exposure to direct sun,” Panigrahi says.
Her mother-in-law does experience a slight discomfort with all the layering protection in the sun, but as she says, it’s a small price to pay. She would rather wear an extra scarf than endure painful red patches, blisters or worse, be confined to the bed for several days, recovering.
The science behind sun allergies
So, why does the sun trigger such a reaction? According to Shayeri Singh and Lola Ali, a dermatologist at Euromed Clinic in Dubai, a sun allergy isn’t exactly an allergy to the sun itself. It’s an immune system response triggered by sunlight. When certain people, for example those who suffer from autoimmune conditions, have pre-existing skin conditions, or even living in temperate climates are exposed to the sun, their immune system mistakenly identifies some components of sun-damaged skin as harmful and kicks into defensive mode, causing reactions like rashes or small blisters. "When such people are exposed to sunlight, the immune system treats the ultra-violet (UV) radiation or its interaction with chemicals on the skin like a threat," she explains. "This leads to inflammation, resulting in redness, itching, rashes, or even blisters on the affected skin.”
While both sun allergy and sunburn result from exposure to sunlight, they are fundamentally different. While sun allergy is an abnormal immune system reaction to sunlight, Sunburn on the other hand is a direct result of overexposure to UV radiation, which damages the DNA in the skin and is purely a response to excessive UV exposure...
This is quite different from a sunburn, which occurs when UV rays damage the outer layer of the skin, explains Ankita Tuknayat, Specialist Dermatology & Cosmetology, Aster Clinic. Sunburns can happen to anyone after prolonged exposure, whereas sun allergies often appear even after brief exposure to sunlight and are mostly localised in areas of the body that were exposed, explain Singh and Tuknayat. The symptoms can worsen, with repeated exposure and vary significantly in severity from person to person.
These allergies are most often triggered by UV rays, specifically UVA and UVB. “These rays penetrate the skin at different depths, with UVA penetrating deeper and contributing to more persistent allergies like polymorphous light eruption (PMLE). For some, even small amounts of UV exposure are enough to provoke a noticeable reaction,” she says.
The different types of sun allergies
Sun allergies come in many forms, each with its own unique triggers, telltale symptoms, and varying levels of severity, making every case a little different and often unpredictable. Abeer Elsayed, a dermatologist specialist breaks down the different kinds of sun allergies:
Polymorphous light eruption (PMLE): Often referred to as sun poisoning, PMLE is the most common sun allergy. It occurs when the skin, unaccustomed to sunlight after prolonged periods of limited exposure, reacts to UV rays. PMLE is more common among people living in temperate climates. A 2014 study published in US-based medical journal Dermatology Clinics noted that people in colder climates, with limited sun exposure during winter, often face sudden reactions when exposed to intense sunlight in warmer seasons.
Symptoms: After sun exposure, people with PMLE often develop reddish patches on their skin that can itch, burn, or sting. While these spots are typically non-scarring, severe cases can escalate, with the rash spreading over large areas of the body. Accompanying symptoms may include headaches, fever, fatigue, and even low blood pressure, making the condition not just uncomfortable but potentially debilitating.
Photoallergic reaction: This kind of reaction occurs when sunlight interacts with a chemical on the skin, commonly found in sunscreen, fragrances, cosmetics, or antibiotic ointments, or with a substance ingested through medication, often prescription drugs, triggering a skin reaction. The most common trigger for a photoallergic reaction is UVA radiation, which penetrates deep into the skin and interacts with these substances, causing the immune system to react. This reaction can be localised or spread to larger areas of the body, depending on where the substance was applied or absorbed. In some instances, the skin eruption may even spread to areas that were covered by clothing. As photoallergic eruption is a type of delayed hypersensitivity reaction, symptoms may not appear until one to two days after sun exposure.
Solar Urticaria: This form of sun allergy produces hives, large, itchy, red bumps, on sun-exposed skin. It usually develops within minutes of sun exposure.
As Dubai-based Afsha Mallory, a dermatology specialist explains, “Each type of sun allergy has unique triggers and symptoms, but essentially, the unifying factor is an exaggerated immune response to sunlight. For effective treatment and prevention, the management strategies vary, from avoiding certain chemicals to immunosuppressive therapies.”
What triggers these reactions?
Sun allergies are triggered, not only by sunlight but also by the body's reaction to UV radiation or its interaction with substances on the skin. "UV radiation is the main trigger," explains Mallory. "UVB rays cause sunburns by damaging the skin’s outer layers, and overexposure can lead to rashes and irritation in people with sun allergies. UVA rays, which penetrate deeper, can also cause allergic reactions like photoallergic eruptions. These rays are present year-round, even on cloudy days."
Certain medications can also heighten the risk of sun allergies. "Photosensitising medication, such as antibiotics or diuretics, can cause skin reactions like rashes or blisters when exposed to UV rays," Mallory advises. "So, if you're taking medications, you need to consult your doctor about additional protective measures." Skincare products containing chemicals that react with sunlight, as well as certain perfumes, can also exacerbate sun allergies. "Be careful with skincare products and check the labels to make sure they’re safe for sun exposure," she adds. Even perfumes can be problematic due to compounds like coumarin and bergamot oil.
Additionally, people with certain underlying health conditions are more susceptible to sun allergies, explain the specialists. These conditions include:
Lupus: Lupus is an autoimmune disease that causes photosensitivity, a condition where exposure to sunlight triggers severe skin reactions. The most characteristic rash associated with lupus is the butterfly-shaped rash that appears across the cheeks and nose. However, photosensitivity in lupus can also cause rashes in other areas of the body, particularly those exposed to the sun, such as the arms, chest, and back. These rashes can range from mild redness to more severe blistering and inflammation, and they may worsen with prolonged sun exposure.
Porphyria: Porphyria is a rare group of disorders caused by a build-up of porphyrins, which are chemicals essential for producing haemoglobin in red blood cells. In some forms of porphyria, the accumulation of these chemicals in the body affects the skin's ability to handle sunlight. This leads to photosensitivity, where exposure to sunlight triggers severe skin reactions.
Eczema or psoriasis: Both eczema and psoriasis are chronic skin conditions that increase the skin's sensitivity, making it more prone to irritation or allergic reactions, especially when exposed to sunlight. Both conditions involve inflammation of the skin, but they respond to sun exposure in different ways. In eczema, direct sun exposure can trigger irritation and worsen inflammation. While moderate sun exposure may initially seem to help by drying out the skin or reducing inflammation, prolonged or excessive exposure to UV rays can exacerbate the condition, leading to flare-ups and increased discomfort. On the other hand, psoriasis, an autoimmune disease that causes skin cells to multiply too quickly, leading to thick, scaly patches, can also be aggravated by excessive sun exposure. Sunburns or overexposure to UV radiation can accelerate the turnover of skin cells, triggering the development of new plaques, the thickened, scaly areas characteristic of psoriasis.
How can you manage sun allergies?
Managing sun allergies might sound tricky, but there are ways to cope. Here are a few expert-approved strategies, explain Ali and Tuknayat.
Apply a broad-spectrum sunscreen with an SPF of 30 or higher before heading outdoors, ensuring it protects against both UVA and UVB rays.
Use a lip balm with SPF 30 or above, specifically designed for lip protection.
Limit your time outside during peak sun hours.
Wear sunglasses with UV protection to shield your eyes from harmful rays.
Opt for long pants, a long-sleeved shirt, and a wide-brimmed hat to cover as much skin as possible.
Be cautious when it comes to skincare products and medications, especially certain antibiotics, that could trigger a photoallergic eruption. If you're on prescription medication and spend a lot of time outdoors, consult your doctor to see if any special precautions are needed to minimise sun exposure while taking the medication.