Allergy Types: Other Allergies: Allergies to Poison Ivy, Oak, and Sumac
Poison ivy, poison oak, and poison sumac are plants that contain an irritating, oily sap called urushiol. Urushiol triggers an allergic reaction when it comes into contact with skin, resulting in an itchy rash, which can appear within hours of exposure or up to several days later. A person can be exposed to urushiol directly or by touching objects – such as gardening tools, camping equipment, and even a pet’s fur — that have come into contact with the sap of one of the poison plants.
Urushiol is found in all parts of these plants, including the leaves, stems, and roots, and is even present after the plant has died. Urushiol is absorbed quickly into the skin. It can also be inhaled if the poison plants are burned. The smoke may expose not only the skin to the chemical but also the nasal passages, throat, and lungs. Inhaled urushiol can cause a very serious allergic reaction.
The rash that results from the poison plants is a form of allergic contact dermatitis. (Dermatitis is swelling and irritation of the skin.) Skin is not automatically sensitive to urushiol. Sensitivity builds up after the skin is exposed to the substance. When initially exposed to urushiol, the skin alerts the immune system of the presence of the irritating chemical. However, it’s common for no visible reaction will occur the first time a person comes in contact with a poison plant. The immune system then prepares a defensive reaction for the next time the skin encounters the substance. This sensitizes the skin so that new contact with urushiol causes an allergic reaction.
Poison ivy, poison oak, and poison sumac can be found in most areas of the U.S., except Alaska, Hawaii, and the deserts of the Southwest. In some areas of the country (East, Midwest, and South), poison ivy grows as a vine. In the northern and western U.S., and around the Great Lakes, it grows as a shrub. Each poison ivy leaf has three leaflets.
Poison oak closely resembles poison ivy, although it is usually more shrub-like, and its leaves are shaped somewhat like oak leaves. The undersides of the leaves are always a much lighter green than the surface and are covered with hair. Poison oak is more common in the western U.S.
Poison sumac grows as a woody shrub, with each stem containing 7 to 13 leaves arranged in pairs. Poison sumac can be distinguished from harmless sumac by its drooping clusters of green berries. Harmless sumac has red, upright berry clusters. Poison sumac is more common in wet, swampy areas.
Poison ivy rash is caused by an oily resin called urushiol — found in the leaves, stems and roots of poison ivy, poison oak and poison sumac. Urushiol is very sticky, so it easily attaches to your skin, clothing, tools, equipment or pet’s fur. You can get a poison ivy reaction from:
- Direct touch. If you directly touch the leaves, stem, roots or berries of the plant, you may have a reaction.
- Touching contaminated objects. If you walk through some poison ivy and then later touch your shoes, you may get some urushiol on your hands, which you may then transfer to your face by touching or rubbing. If the contaminated object isn’t cleaned, the urushiol on it can still cause a skin reaction years later.
- Inhaling smoke from the burning plants. Even the smoke from burning poison ivy, poison oak and poison sumac contains the oil and can irritate or harm your nasal passages or lungs.
A poison ivy rash itself isn’t contagious. Blister fluid doesn’t contain urushiol and won’t spread the rash. In addition, you can’t get poison ivy from another person unless you’ve had contact with urushiol that’s still on that person or on his or her clothing.
Some people are extra-sensitive to the oil that causes poison ivy rash, and this tendency appears to run in families.
Outdoor occupations and hobbies can put you at higher risk for exposure to poison ivy, poison oak or poison sumac. Examples include:
- Construction workers
- Cable or telephone line installers
The diagnosis of this rash is typically made by a health-care professional after obtaining a thorough history and performing a detailed exam of the skin. While some individuals will know and report exposure to poison ivy, oak, or sumac, others may not be aware of it and may not recall any exposure. The appearance of the characteristic rash is usually all that is needed to make the diagnosis. No blood tests or imaging studies are necessary.
Self-care for a mild rash includes:
- Wash the area well with mild soap and lukewarm water as soon as possible after contact.
- Wash all clothes, shoes, socks, tools, pets, and toys that may have become contaminated.
- Cool compresses may help during the blistering phase.
- Use a topical corticosteroid cream on the rash as directed by your doctor.
- Try calamine lotion for the itching, but avoid skin products that contain anesthetics or antihistamines, which can cause their own allergic reaction.
- To help relieve the itch, try cool showers or a mixture of baking soda and water applied to the area. If sleep is a problem because of the itching, try an over-the-counter antihistamine at night.
Call your doctor or a dermatologist for:
- Severe blistering, swelling, and itching
- Symptoms in sensitive areas such as the eyes, lips, throat, or genitals
- A rash over large areas of your body
- A rash lasting longer than a week to 10 days
- Blisters that become infected with pus
Get immediate medical help for any difficulty breathing or severecoughing after exposure to burning plants.
In some cases, an oral steroid or other medication may be needed to relieve severe symptoms.
Like most allergic reactions, treatment is dictated by the severity of the reaction. Reactions that cover a large proportion of the body, make someone uncomfortable enough to disrupt normal activities, or do not get better within a few days may require treatment withprescription medications.
Medications for Poison Ivy, Oak, and Sumac Rash
- Topical corticosteroid creams (prescription strength): These reduce the immune response and relieve inflammatory symptoms.
- Oral corticosteroid medication (such asprednisone): These have effects similar to those of the creams but are needed for a more severe or widespread reaction. A course of steroids can run from three days to as long as four weeks.
- Oral antihistamines — for itching: The main advantage of the prescription antihistamines is that they do not make people sleepy, allowing the individual to carry on his or her normal activities, although some types of second-generation (nonprescription) antihistamines are available over the counter.
- Antibiotics: These are needed only if the skin becomes infected with bacteria after the initial rash.
To prevent poison ivy rashes, follow these tips:
Avoid the plants
Learn how to identify poison ivy, poison oak and poison sumac. When hiking or engaging in other activities that might expose you to these plants, try to stay on cleared pathways. If camping, make sure you pitch your tent in an area free of these plants.
Keep pets from running through wooded areas so that urushiol doesn’t accidentally stick to their fur, which you then may touch. If you think your pet may be contaminated with urushiol, put on some long rubber gloves and give your pet a bath.
Remove or kill the plants
In your backyard, you can use an herbicide to get rid of poison ivy or use heavy gloves to carefully pull it out of the ground. Afterward, remove and wash your gloves and hands thoroughly. Don’t burn poison ivy or related plants because the urushiol can be carried by the smoke.
Wash your skin
Gently washing off the harmful resin from your skin, using any type of soap, within five to 10 minutes after exposure may help avert a reaction. After an hour or so, however, the urushiol has usually penetrated the skin, and washing won’t necessarily prevent a reaction, but it may help reduce its severity. Be sure to wash under your fingernails too.
Clean contaminated objects
Wearing long pants, socks, shoes and gloves will help protect your skin, but be sure to wash your clothing promptly with detergent — ideally in a washing machine — if you think you’ve come into contact with poison ivy. Handle contaminated clothes carefully so that you don’t transfer the urushiol to furniture, rugs or appliances.
In addition, wash any other contaminated items — such as outdoor gear, garden tools, jewelry, shoes and even shoelaces — as soon as possible. Urushiol can remain potent for years. So if you put away a contaminated jacket without washing it and take it out a year later, the oil on the jacket may still cause a reaction.
Apply a barrier cream
Before potential exposure to poison ivy, you might want to try an over-the-counter skin cream containing bentoquatam (IvyBlock). Bentoquatam absorbs urushiol and prevents or lessens your skin’s reaction to the oil.
If someone is exposed to any of these plants or their oils, wash thoroughly with soap and water as soon as possible. An alternative is rubbing alcohol, which can dissolve and remove the oils from the skin. If the oil is removed within 10 minutes, it’s much less likely a rash will develop.
Symptoms from a mild rash can sometimes be relieved by the following home remedies:
- Cool compresses with water or milk
- Calamine — a nonprescription lotion
- Aveeno oatmeal bath — a product that’s put in the bath to relieve itching
- Oral antihistamines such asdiphenhydramine (Benadryl) — Caution: These medications may make someone too drowsy to drive a car or to operate machinery safely.
Nonprescription corticosteroid (for example, hydrocortisone) creams usually do not help.
Do not use bleach to cleanse rash from poison ivy, oak, or sumac. These areas are open wounds, and bleach is a harsh substance that can damage the skin and slow the healing process.
Do not attempt to treat severe (or anaphylactic, see above) reactions or to “wait it out” at home. Go immediately to the nearest emergency department or preferably, call 911 and take an ambulance. Here are some things to do while waiting for the ambulance:
- Stay calm.
- Prevent further exposure to the “poisonous” plant.
- Take an antihistamine (one to two tablets or capsules of diphenhydramine [Benadryl]) if it’s possible to swallow without difficulty.
- If someone is wheezing or having difficulty breathing, use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) if one is available. These inhaled medications open up (dilate) the airway.
- If someone is feeling lightheaded or faint, lie down and raise the legs higher than the head to help blood flow to the brain.
- If someone has been given an epinephrine kit (EpiPen) for a previousallergic reaction, inject oneself as instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms (see Follow-up).
- If at all possible, someone should be prepared to tell medical personnel what medications the afflicted individual takes and his or her allergy history.
The prognosis for poison ivy, oak, or sumac rash is generally good. The rash and itching usually get better gradually and go away completely in two to three weeks. Treatment should be continued at least this long because the rash can come back if medicines are stopped too soon. There may be temporary darkening of the skin when the rash disappears.
A complication of poison ivy, oak, or sumac rash is infection, which usually happens as a result of scratching the skin. Redness, pain, and pus surrounding a rash can indicate a skin infection, which a doctor can treat with antibiotics. This is more likely to happen if the rash is scratched so much that the skin is broken.
Someone will almost certainly will have another reaction if he or she comes in contact with these plants again after a first reaction.
If you scratch a poison ivy rash, bacteria under your fingernails may cause the skin to become infected. See your doctor if pus starts oozing from the blisters. Treatment generally includes antibiotics.