FAQ: Pesky Rashes From Plants

An expert answers questions about preventing and treating rashes you can get from common plants.

Feb. 4, 2011 (New Orleans) -- What may start as a seemingly harmless day of gardening can quickly take a turn for the worse when common plants make their mark on your skin.

While many of the skin reactions resulting from contact with a hazardous plant are more of a nuisance than anything else, others can cause severe or long-lasting effects that require medical attention.

At the meeting of the American Academy of Dermatology, Julian J. Trevino, MD, associate professor of dermatology at Wright State University Boonshoft School of Medicine in Dayton, Ohio, discussed common skin reactions that can occur when you come in contact with plants as well as effective treatments and preventive strategies.

What are some of the common skin reactions caused by exposure to plants?

Some people break out in hives simply by brushing up against stinging nettle plants. The stems and leaves have sharp hairs resembling little hypodermic needles. When the skin comes in contact with these hairs, the chemical histamine or acetylcholine is released, causing an outbreak of hives within 30 to 60 minutes of exposure. Most people experience a mild reaction that resolves on its own in a few hours, but one patient died.

Many plant-related rashes are caused by plants containing spines, thorns, or small emergences called glochids. These plants include cacti and prickly pear, figs, mulberries, thistles, and saw palmetto.

If the spine gets under your skin, it can cause itchy, bumpy eruptions. The rash is typically innocuous, but you can develop a staph or fungal infection if microbes are present on the prickly spine that enters the skin.

Perhaps the most well-known and feared plants linked to skin rashes and irritation are poison ivy, oak, and sumac. These plants contain a resinous sap called urushiol that causes a rash when it comes in contact with the skin in about 50% of adults in North America.

But direct contact with poison ivy and its variants is not the only way that you can get this bothersome rash. When a poison ivy plant is injured in any way, the urushiol is released quickly and can stick to anything around it. That means that you can develop [a] poison ivy [rash] if you pet your dog after he has come in contact with the plant, or if you touch a gardening tool or piece of clothing that has come in contact with poison ivy.

Even airborne contact is possible, especially in the fall or winter when these poisonous plants are burned among other brush, and particles of urushiol are released into the air. If the airborne particles land on your skin or you inhale them, you can get a widespread rash and severe irritation in the respiratory tract.

The rash, which presents like itchy red patches, often accompanied by blisters arranged in streaks, typically surfaces [within hours] to four days after exposure. It doesn't always come on at the same time. People often mistakenly assume a new rash means they were exposed again.

Many people who are allergic to poison ivy are also allergic to oil from cashew nut tree shells, the skin of mangoes, and the black sap of the Japanese lacquer tree. Polymerized urushiol can persist in lacquered furniture and cause allergies for hundreds of years.

How should you treat plant allergies?

That depends on the plant and the reaction.

In the case of cacti or other spiny plants, the spine should be carefully removed from the skin, usually with tweezers. If it's a really small spine or glochid, apply glue and gauze to the site, allow it to dry, and peel it off.

Minor itching, irritation, or rash can be typically treated with an oral antihistamine or over-the-counter topical steroid. But if a rash doesn’t respond to over-the-counter treatments, you should see a dermatologist. In cases where a rash is accompanied by more severe reactions such as difficulty in breathing or swallowing, go to the emergency room immediately.

If you come in contact with poison ivy, rinse the skin with water immediately. About 50% of the urushiol will come off if you rinse within 10 minutes. But avoid soap; it can spread the resin.

Lukewarm baths and soaks with products containing aluminum acetate (a type of salt that dries up the blisters and any weeping) and topical preparations such as calamine or topical steroids are helpful in treating a poison ivy rash.

While oral antihistamines will help alleviate itching and skin irritation, topical antihistamines should be avoided as some people are allergic to them and the rash could get worse.

In cases in which a rash is severe or covers a large area of the body, a dermatologist may prescribe strong topical steroids or a two- to three-week course of oral steroids.

How can I prevent skin reactions?

You may not always be able to prevent them, but you can minimize the risk. I give my patients these tips: 

  • Wear protective clothing whenever possible, including gloves (preferably vinyl gloves), long sleeves, and long pants tucked into socks. 
  • Apply an over-the-counter barrier cream or lotion containing quaternium-18 bentonite to exposed skin before going outdoors. This helps prevent urushiol from poisonous plants from contacting the skin. 
  • Avoid poisonous plants. Poison ivy, poison oak, and poison sumac are recognizable due to their three-leave groups. Remember this phrase: "Leaves of three, let it be."
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