Mayo Clinic Health Library

Slide show: Poison ivy and other summer skin irritants

Updated: 05-07-2011

Poison ivy

Photo of poison ivy plant and rash

Can you recognize the most common summer skin irritants?

Poison ivy grows as vines or low shrubs in most climates. Each leaf on a poison ivy plant has three smaller leaflets. Contact with any part of the poison ivy plant can cause red, swollen skin, blisters and severe itching, sometimes within hours after exposure.

A poison ivy rash usually resolves on its own within a few weeks. In the meantime, control itching with an over-the-counter anti-itch cream, such as calamine lotion or hydrocortisone cream. Oatmeal baths and cool compresses also might be helpful. Consult your doctor if you have a severe poison ivy rash or if the rash involves your eyes, face or genital area.

Poison oak and poison sumac cause a similar rash.

Ragweed

Photo of ragweed plant and rash

Ragweed plants usually grow in rural areas or open meadows. Ragweed pollen is a primary cause of hay fever (allergic rhinitis). For those who are sensitive to ragweed, ragweed exposure can also cause a rash. You might notice small, itchy bumps and blisters. A ragweed rash usually develops within two days of exposure and resolves on its own within two to three weeks, as long as you avoid any additional ragweed exposure. In the meantime, control itching with an over-the-counter anti-itch cream, such as hydrocortisone cream. Consult your doctor if the rash is painful or lasts longer than three weeks.

Wild parsnip

Photo of wild parsnip plant and reaction

Wild parsnip grows in sunny areas, often along highways and in prairies. The plant bears large, flat clusters of yellow-green flowers on a thick stem. Sap from the wild parsnip plant — along with exposure to sunlight — can cause a burn-like reaction on the skin. Within a day after exposure, the skin turns red and may blister. The affected area, which feels like a mild to severe sunburn, often turns brown. This discoloration sometimes lasts for months.

Soothe the affected area with a cool, wet cloth. Consult your doctor if the reaction is painful or the blisters are severe or last longer than a couple of weeks.

Heat rash (miliaria)

Photos of heat rash

Heat rash develops when the sweat ducts become blocked and perspiration is trapped under your skin. Miliaria rubra (A), one type of heat rash, appears as red clusters of small blister-like bumps that can produce a stinging sensation. Miliaria crystallina (B), another type of heat rash, appears as clear, fluid-filled bumps that produce no other signs or symptoms. Heat rash is most common in skin folds and wherever clothing causes friction.

Heat rash isn't serious and usually resolves quickly when the affected area cools. In the meantime, reduce sweating by staying in an air-conditioned space or using fans to circulate the air. Wear lightweight clothing and limit physical activity.

Polymorphous light eruption (PMLE)

Photo of polymorphous light eruption (PMLE)

Polymorphous light eruption (PMLE) is a rash that occurs as a result of sensitivity to sunlight (photosensitivity). Within hours of sun exposure — usually in the spring or early summer — you may notice an itchy, red rash. The spots occur most often on the front of the neck and chest as well as the arms and thighs.

PMLE usually resolves on its own within a few days, although the condition can recur. In the meantime, limit sun exposure. Ease any discomfort with a cool compress or an over-the-counter anti-itch cream, such as hydrocortisone cream. Consult your doctor if the reaction is severe or painful.

Tinea versicolor

Photo of tinea versicolor

Tinea versicolor is a common fungal infection that results in small patches of discolored skin. Tinea versicolor is most common in warm, humid weather. The patches — which are often white or tan and may be itchy — grow slowly and may be more noticeable after sun exposure. The patches usually develop on the back, chest or upper arms and can cause mild itching.

Tinea versicolor can be treated with over-the-counter antifungal creams, lotions or shampoos. Skin color may remain uneven for several weeks, however, and the infection may return — especially in warm, humid weather.

Swimmer's itch

Photos of swimmer's itch

Swimmer's itch is an itchy rash caused by certain parasites that normally live on waterfowl and freshwater snails. On warm, sunny days — especially in calm freshwater lakes or ponds — these parasites can be released into the water. While you swim, the parasites might burrow into your skin. The parasites soon die — and you're left with itchy, red, raised spots on your skin.

Swimmer's itch usually resolves on its own within a few days. In the meantime, control itching with an over-the-counter anti-itch cream, such as hydrocortisone cream. Consult your doctor if the itching is intense or the rash lasts longer than a week.

Chigger bites

Image of chigger bites

Chiggers are tiny mites found in tall grass and weeds. If you brush against infested plants, chiggers may attach to your skin. They fall off after a few days, leaving behind red, itchy welts.

Chigger bites usually heal on their own within one to two weeks. In the meantime, control itching with an over-the-counter anti-itch cream, such as hydrocortisone cream. Consult your doctor if your skin appears infected or if the bites seem to be spreading to other parts of your body.

Lyme disease

Photos of Lyme disease rash

Lyme disease is a tick-borne illness that causes a distinctive rash, flu-like symptoms and aching joints. The rash begins as a small, red bump (A) that appears within a few days to a month after a tick bite. Over the next few days, the redness expands and may resemble a bull's-eye (B). Fever, chills, fatigue, headache and body aches may accompany the rash.

If you suspect that you've been bitten by a tick and experience signs and symptoms of Lyme disease, contact your doctor immediately. Treatment is most effective if begun early. Left untreated — even if the signs and symptoms resolve on their own — Lyme disease can cause serious complications involving the heart, joints and nervous system.

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