Poison ivy rash: What's to know
Also known as Toxicodendron radicans, poison ivy is native to North America and is a member of the cashew family.
It mainly grows on the edges of woodland, in areas where there is plenty of sunlight. Poison ivy is a shrub, so it is generally of low height. It may produce green berries, and green-yellow flowers typically grow in spring.
People can identify the plant by its compound leaves that consist of three leaflets and range from light to dark green. Each leaf grows on its own stem and connects to the main vine. There are no thorns. Poison ivy is not a true ivy, but it tends to climb telephone poles and trees.
"Leaflets three, let it be" and "hairy vine, no friend of mine" are two common mnemonic rhymes that people use to recognize poison ivy.
According to the American Academy of Dermatology, 85% of the population in the United States will have an allergic reaction to poison ivy. If these people touch the plant, they will develop a rash.
The remaining 15% may not react to poison ivy. However, even those who have never reacted to it should take care, as repeated exposure to the plant can increase the likelihood of a reaction.
What's poisonous about poison ivy?
Poison ivy contains urushiol, an oil that can cause a rash on human skin.
Poison ivy sap is present in nearly every part of the plant, including the leaves, stems, and roots.
The sap contains an oil called urushiol, which is a pale yellow, sticky, oily substance that is also present in poison oak and poison sumac.
If any of this oil touches the skin, a blistering skin rash can develop.
A person can react to urushiol after:
- touching the plant
- touching contaminated objects, such as shoes that have come into contact with the plant
- breathing in smoke from burning poison ivy
The most dangerous type of exposure is when a person inhales the smoke from a burning plant.
Stinging nettles can cause a reaction, but they can also be useful. Find out more about this plant here.
The rash usually appears within 3 days of the exposure to the oil, but the time frame can vary significantly. The more sensitive a person is to poison ivy, the faster the rash may appear.
Signs of a reaction include:
- intense itching
- red skin or red streaks
- red bumps, which are called papules
- blisters, often developing in lines and oozing
- crusting skin
The rash is not contagious, and it does not spread to other areas of the body. If it appears to be spreading, this will be due to a delayed reaction or further contact with objects that remain contaminated.
It can take several weeks for the rash to heal.
When to see a doctor
If any of the following signs or symptoms occur, a person should seek immediate medical attention:
- trouble breathing
- difficulty swallowing
- a swollen tongue
- a rash covering the face, the genitals, or most of the body
- swollen eyelids, to the extent that the eyes close
A serious allergic reaction can occur in the nasal passages, throat, and lungs, leading to breathing difficulties. A person who has trouble breathing needs immediate medical care.
Image credit: CDC/ Richard S. Hibbits, 1971
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Image credit: Etereve, 2009
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Image credit: Adam Rosenberg, 2010
A poison ivy rash usually disappears within 2–3 weeks without treatment. Several prescription treatments are available, and general treatment measures exist.
People can also relieve the symptoms using the following tips:
Remove clothes and take a shower when coming in from outside. Rinsing the skin with only water within 1 hour of contact with the plant might help remove the urushiol. However, it is best to wash as soon as possible. If a person waits 10 minutes after the exposure to wash, only about 50% of the urushiol will come off. Over time, a person will be increasingly unlikely to be able to wash off this substance.
Soak in cool water to ease burning and itching, but avoid warm or hot water. A cool oatmeal bath may help.
Make cool compresses by soaking a clean washcloth in cold water. These may help soothe the itchy skin.
Apply calamine and cortisone creams to help reduce itching. These are available over the counter.
Oral antihistamines, such as fexofenadine (Allegra), cetirizine (Zyrtec), or diphenhydramine (Benadryl), can ease inflammation and itching, and they are available over the counter.
Zyrtec and Benadryl can both cause drowsiness, so people should avoid taking them during the day if they need to be awake and alert. Taking oral antihistamines before bed may help the person sleep better, as the itch can be intense and interrupt sleep.
Oral corticosteroids may be necessary if the person has a severe rash and a large number of blisters. They may also inject the corticosteroid directly into a person's muscle to stop the reaction from progressing further.
The person should not scratch the rash or burst any blisters, as this can lead to infection. If the rash does become infected, a doctor may prescribe oral or topical antibiotics.
Various preparations that people can use before and after contact with poison ivy are available for purchase online:
Some people use natural antihistamines for their allergies. Learn more here.
Risk factors and prevention
Gardeners should wear gloves if they have to work near areas with poison ivy.
People with the highest risk of a poison ivy reaction include those who spend a lot of time outdoors, either for work or for hobbies, as this can increase exposure.
People whose work may expose them to poison ivy include:
- foresters and farmers
- gardeners and landscapers
- construction workers
Tips for reducing the risk
A person can reduce their risk of having a poison ivy reaction by:
- learning to identify the plant so that they can avoid it
- wearing long pants, socks, and gloves when working or doing activities outdoors
- cleaning all clothing and shoes after being outdoors if there is poison ivy around
- washing the skin immediately with water after possible exposure and rinsing thoroughly
- scrubbing under the nails after possible exposure
- cleaning pets thoroughly if they may have been in contact with poison ivy, as they can carry urushiol on their skin and coat
Pets can also be sensitive to the toxin, so people should keep them away from poison ivy where possible.
Even a person who does not usually have a reaction should use gloves and take care when handling poison ivy, as the risk of a reaction increases with age and repeated exposure.
They should also take care to remove their outdoor clothing and wash it thoroughly, as the sap on their clothes can transfer to other people who may have a reaction.
Products are available both to act as a barrier before exposure and to provide relief afterward. Applying a skin cream containing bentoquatam (IvyBlock) before exposure may help stop urushiol from affecting the skin
Some homeopathic products, such as Be gone Poison Ivy, claim to relieve the symptoms of a poison ivy reaction. However, the National Institutes of Health note that the Food and Drug Administration (FDA) have not evaluated this medication on the basis that there is no scientific evidence to support its use.
Poison ivy is a common plant in North America, and it causes an allergic reaction in many people. If the reaction is severe, it can be life-threatening.
People should learn how to recognize poison ivy, find out where it grows around their local area, and ensure that they know what to do if exposure occurs.
I have had a strong reaction to poison ivy in the past. Do you recommend using over-the-counter products to prevent a reaction?
The best way to prevent a reaction to poison ivy is to avoid the allergen, urushiol, and protect your skin.
The American Academy of Dermatology also recommend using a topical treatment with bentoquatam in it, which may help prevent the skin from absorbing urushiol. There are also other homeopathic medications that some have found helpful for preventing a reaction.
These medications require more studies to confirm their safety and efficacy before a doctor can recommend them. As always, it is important to speak to a doctor or dermatologist before taking any new medications, including over-the-counter drugs.Owen Kramer, MD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.