8 Unexpected Causes of Summertime Rashes

Whether frozen or on the rocks, margaritas can be a refreshing summer cocktail, but they may lead to more than a potential hangover. A dribble of citrus juice on skin that’s been exposed to the sun can quickly lead to a nasty burn called phytophotodermatitis, sometimes known as margarita dermatitis. It happens when a photosensitizing compound in limes called furocoumarin — also found in other citrus fruits as well as parsley, dill, celery, and a number of other plants — becomes activated by ultraviolet A (UVA) light, causing a burning rash within hours.

You may develop blisters or red, itchy patches on your skin, with symptoms at their worst within two or three days. Since only the areas of your skin that came in direct contact with the juice are affected, the rash may appear as drips, streaks, or other irregular patterns. As the blisters heal, your skin may become darker (hyperpigmented) — an effect that can take months to go away. Ask your doctor about using a topical steroid cream and a cold compress to ease the pain.

To help prevent margarita dermatitis, wash your hands after handling limes and rinse off citrus juice immediately if you’re in the sun — even if you’re wearing sunscreen, since you can still get burned. “Sunscreen doesn’t protect against UVA as well [as it does] UVB,” says Bruce Robinson, MD, a board-certified adult and pediatric dermatologist and a clinical professor of dermatology at Lenox Hill Hospital in New York City.

Notice a rash under your swimsuit after a dip in the ocean? You may have seabather’s eruption, also known as pica-pica (which is Spanish for "itchy-itchy") or sea lice. This occurs when tiny thimble jellyfish and sea anemones become trapped underneath your swimsuit and release stinging cells that inject a toxin, causing an allergic reaction in your skin. You may notice a prickly sensation while you’re swimming. Within 4 to 24 hours, a patch of itchy red bumps that look a bit like insect bites or hives appear in areas covered by your swimsuit. “Until they dissolve, they cause intense itching,” says Dr. Robinson.

Thimble jellyfish and sea anemones are most common on the southeast coast of the United States all the way up to New York, as well as in the Gulf of Mexico and the Caribbean. Lifeguards often notify swimmers with sea lice warning signs at public beach access points. The rash is more common in the spring and summer and in kids under 15, as well as surfers, who often spend more time in the water.

Because these creatures tend to eject their poison in water, it’s a good idea to remove your swimsuit and shower immediately after a swim in the ocean. Rinse your suit thoroughly in hot water to remove any remaining organisms. Ask your doctor about using an antihistamine or topical cortisone to relieve the itch. (Just be careful before using in children, and avoid using creams on the groin and face.)

The rash from swimmer’s itch differs from seabather’s eruption because it crops up in areas that aren’t covered by swimwear. This occurs when microscopic parasites from infected snails living in the warm, shallow water of lakes, streams, or the ocean burrow into the skin, causing an allergic reaction that appears as tiny red bumps or large red welts. “We’re dead-end hosts, so [the parasites] die in the skin. The real problem is the intense itching that can come with it,” says Robinson.

To help relieve the itch, take a bath with Epsom salts or ground oatmeal, or apply a baking soda paste or a cool compress to affected skin. If the itch persists, ask your doctor if an over-the-counter antihistamine or topical cortisone may help.

You can avoid swimmer’s itch by looking for signs warning of infested water and staying out of marshy areas where snails live. Parasites tend to enter the skin as water evaporates, according to the American Academy of Dermatology. (AAD), so briskly rub your skin with a towel as soon as you get out of the water, then remove your bathing suit and shower as soon as possible.

One or two days after soaking in water that’s contaminated with a common bacterium called Pseudomonas aeruginosa, found in the ground and water, you may develop a skin rash that’s known as hot tub folliculitis. It’s more common in hot tubs (hence the name), because hot water breaks down the chlorine that kills bacteria. But the rash can also occur after swimming in a poorly maintained pool or contaminated lake, according to the Centers for Disease Control and Prevention.

Symptoms of hot tub folliculitis include an itchy red rash of tiny millimeter-size bumps that’s worse in areas covered by a swimsuit. You may also notice itchy or tender pimples around hair follicles. While the rash usually gets better on its own, see a doctor if it doesn’t disappear in a few days; you may need to take antibiotics.

The best way to prevent hot tub rash is to check the chlorine and bromine levels in the water before you take a dip. When you get out of the water, shower with soap right away and clean your suit in hot water.

Also known as prickly heat or miliaria, heat rash happens when sweat gets blocked in your pores and builds up under your skin. It’s particularly a problem in babies but can happen at any age, especially when it’s hot and humid outside.

Heat rash stings or itches, and usually appears as small red bumps or clear blisters that break easily. “You’d see a rash on areas where you sweat more,” says New York City–based board-certified dermatologist Sapna Westley, MD. The rash crops up most in areas where skin rubs together, like the armpits, elbows, and groin.

Heat rash typically clears on its own. You can help ease the itch by removing tight-fitting clothing and cooling off your skin. Taking steps to sweat less — such as wearing loose-fitting, lightweight cotton clothing; using lightweight moisturizers like lotions rather than heavier creams or ointments; and staying in the shade or an air-conditioned building when it’s hottest outside — can help prevent heat rash.

People with a sensitivity to sunlight who are exposed to increasingly intense UV rays in the late spring and early summer may break out in very itchy, hivelike bumps known as polymorphous light eruption (PLE). The rash typically appears on the chest, neck, arms, and face.

Research suggests that 10 percent of the general population is affected by PLE, most likely people who live in northern versus southern climates. Three-quarters of the time it starts in females age 20 to 40, according to other data. Those with fair skin are also more susceptible.

This hypersensitive reaction to the sun should go away on its own within 10 days. It usually appears only once each season — as the weather warms up, the skin gets used to UV light. “Over the span of the summer, it tends to get better, but you still have to be careful on vacation and beach days by using sun protection and staying in the shade,” says Dr. Westley. You may, however, notice it crop up again at the same time each year with the changes in season.

To relieve the itch, ask your doctor about taking an antihistamine or applying itch cream. In severe cases, your doctor may prescribe a topical corticosteroid. Your best bet is prevention: Stay in the shade as much as possible when the sun is brightest, between 10 a.m. and 2 p.m. When you’re outside, cover your skin with light-colored clothing and apply SPF 30 or higher sunscreen on any exposed areas.

Cold sores are a viral infection of tiny fluid-filled blisters on or around the lips. If you’ve had cold sores previously, you may notice that recurrences are more common in the summer due to exposure to sunlight. “People don’t often know that the sun is a trigger,” says Robinson.

Don’t forget to use sunscreen on your lips, especially if you have a history of herpes. If you feel a cold sore coming on, let your doctor know. Taking an antiviral drug within the first 24 to 36 hours after symptoms start helps prevent or slow the breakout.

Tinea versicolor is a fungal skin infection. “In general, fungal infections are more common in summer, as fungus thrives in the humidity,” says Westley. This infection appears as white, pink, red, tan, or brown spots, according to the AAD. It can be dry and itchy, but it is benign and not contagious.

“This fungus is more classically seen in the summer, and it often appears on the torso as you sweat more,” Westley explains. Antifungal topical products can eliminate the fungus, though oral antifungals may be used if needed, according to research. Your skin may remain hyperpigmented for a while.

The Takeaway

Rashes are irritated areas on the skin that can lead to swelling, blisters, itchy patches, or allergic reactions. Depending on their cause, they may be treated with colloidal oatmeal, antihistamines, topical cortisones, antibiotics, and antifungal or antiviral medications. Consult your healthcare provider for the best treatment options, especially if the rashes are painful or progress rapidly.

With additional reporting by Jessica Migala.