If you keep a spare tub of aloe vera in your medicine cabinet or fear the thought of braving the beach without an umbrella, you’ve probably experienced the uncomfortable sting and peeling that comes with a bad sunburn. However, for some, a pesky rash that pops up after sun exposure might indicate something else: a sun allergy.

There are multiple types of sun allergies, but the most common — estimated to affect up to 20 percent of the global population — is called polymorphous light eruption, or PMLE. While some rarer sun allergies, such as porphyria (often called “vampire disease”), can make people severely ill, PMLE is a mild condition. It flares up after sun exposure, causing an “itchy, blotchy, unsightly eruption of coalescing red bumps,” says Dr. Orit Markowitz, a dermatologist in New York City.

It can be difficult to figure out if you’re dealing with PMLE because many other skin issues cause similar symptoms. Here’s everything you need to know about PMLE to feel comfortable in your skin this summer. 

So, how does PMLE work?

For those susceptible to PMLE, experts believe sun exposure causes UV rays to alter a compound in the skin. This makes your body produce a round of antigens, which spur a reaction within a few hours to days after that initial sun exposure. 

“It’s a little bit different than the allergic reaction you see in poison ivy, because it’s delayed,” says Dr. Rebecca Thiede, an Arizona dermatologist.

While sunburn causes actual damage to your skin cells, PMLE is just a delayed hypersensitivity to the sun. The rash usually occurs on areas more likely to get sun, like your hands, arms, face or neck — and it clears up in a few weeks without scarring.

It’s much patchier than a sunburn, and one of its most frustrating elements is that you can still develop a reaction if you’re indoors, near a window. People have reported reactions from things as benign as driving on a sunny street. 

Why do some experience PMLE — and others don’t?

If you had always been OK going out into the sun from an early age, and suddenly develop a bumpy rash after sun exposure in your early twenties, that’s actually completely normal. 

Although PMLE can affect people of all ages, it usually starts to appear between the ages of 20 and 40. In terms of seasonality, the allergy begins wrecking its havoc in early spring, lasting throughout summer. And it’s more likely to affect women, as well as people living in northern climates.

“If you’re getting exposure to the sun every day of the year, you’re going to build up more of a tolerance than someone who is exposed less frequently,” says Thiede.

That being said, even if you live in a climate with a lot of sunshine, you can still get PMLE. Although its direct cause is not yet completely understood, genetics are believed to play a large role in susceptibility. One in five people who experience PMLE also has a relative that reacts to the sun. 

What does treatment look like?

If you suspect you may be experiencing PMLE, you should set up an appointment with a dermatologist to rule out more serious conditions. At your appointment, you’ll likely be asked about your medical history and undergo a thorough skin examination.

“I think a lot of patients out there who are experiencing this don’t come to see us,” Thiede says. “It’s startling how often it does happen. I think it’s something that’s underdiagnosed.”

Sunscreen is essential to preventing sun allergy rashes. Theide recommends staying away from chemical sunscreens, and using broad-spectrum, high-SPF, mineral topicals, with ingredients like zinc and titanium dioxide. Experts also recommend covering up with clothing: If you’re not reapplying sunscreen enough, UV rays can still find their way into gaps in your application. 

If you’re experiencing a bad bout of PMLE, and can’t seem to find relief, a dermatologist would likely recommend taking benadryl and applying aloe vera. More serious cases may require topical steroids or prescription allergy medication. 

“This is not something that can’t be managed, prevented,” Markowitz says. “Patients don’t have to suffer from it. They can get support and it can be easily treated.” 

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