Allergy: Poison Ivy, Oak, and Sumac

More than half the people in the United States are sensitive to poison ivy, poison oak, and poison sumac. If you are sensitive, you can develop an itchy, blistering rash by coming into contact with these plants.

• Whether you are working or just enjoying the outdoors, look out for these plants:

• Poison ivy is generally found east of the Rocky Mountains, growing as vines or shrubs. The leaves can have either smooth or notched edges and are often clustered in groups of 3.

• Poison oak is more commonly found west of the Rockies, usually as a small bush but sometimes as a climbing vine. Its leaves are smooth-edged and cluster in groups of 3, 5, or 7.

• Poison sumac is most often found in wet areas of the Southeast. The leaves are generally smooth and oval-shaped, with 7-13 growing on each stem.

• The appearance of each of these plants can vary considerably from region to region, and with the seasons. Even dead plants in underbrush can transmit the toxic oil to your skin.

The rash caused by poison ivy, oak, and sumac is an allergic skin reaction to an oil, called urushiol, which is in the plant. This oil is found in all parts of the plant, including the leaves, stems, roots, and berries.

• Exposure to the oil occurs through any of the following:

• Touching any part of the plants

• Touching clothing or other objects that have contacted the plants

• Touching pets or other animals that have contacted the plants

• Exposure to the smoke of burning plants

• For more information about how these reactions occur, see Allergic Reactions and Contact Dermatitis.

• Exposure to poison ivy, oak, or sumac causes an itching rash that usually appears within 24-72 hours.

• The rash usually starts as small red bumps, and later develops blisters of variable size. The rash may crust or ooze.

• The rash may be found anywhere on the body that has contacted the oil from the plant. It can have any shape or pattern, but is often in straight lines or streaks across the skin.

• Different skin areas can break out at different times, making it seem as if the rash is spreading.

• Contrary to popular belief, leakage of blister fluid does not spread the rash. It is spread only by additional exposure to the oil, which often lingers on hands, clothing and shoes (which are often overlooked as carriers), or tools.

See your health care provider if you have the following conditions:

• Large areas of rash causing significant discomfort
  
  
• Rash on your mouth, genitals, or around your eyes
  
  
• An area of the rash that becomes infected or drains pus
  
  
• A great deal of swelling

People who are highly sensitive to these plants can get a severe reaction, called anaphylaxis.

• If you have swelling of the face and throat or difficulty breathing, feel dizzy or faint, or lose consciousness, you may be having an anaphylactic reaction.
  
  
• If you have any of these symptoms, go immediately to a hospital emergency department.
  
  
• Do not attempt to drive yourself; if no one is available to drive you immediately, call 911 for emergency medical treatment.
  
  
• While waiting for the ambulance to come, begin self-treatment measures.
  
  

Your health care provider can usually make this diagnosis by the appearance of the rash alone. He or she will ask you some questions about the reaction, your symptoms, and your medical history.

No lab tests or x-rays are needed except under unusual circumstances.

Usually self-care at home is all that is needed for a reaction to these plants.

|Self-Care at Home|

If you are 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 your skin. If you can remove the oil within 10 minutes, you are unlikely to develop the rash.

Symptoms from a mild rash can sometimes be relieved by the following:

• Cool compresses with water or milk

• Calamine - A nonprescription lotion

• Aveeno oatmeal bath - A product you put in the bath to relieve itching

• Oral antihistamines such as diphenhydramine (Benadryl) - Caution: these medications may make you too drowsy to drive a car or operate machinery safely
  
  

Nonprescription corticosteroid (eg, hydrocortisone) creams usually do not help.

Do not attempt to treat severe reactions or to "wait it out" at home. Go immediately to the nearest emergency department or call an ambulance. Here are some things to do while waiting for the ambulance:

• Try to stay calm.

• Prevent further exposure to the "poisonous" plant.

• Take an antihistamine (1-2 tablets or capsules of diphenhydramine [Benadryl]) if you can swallow without difficulty.

• If you are wheezing or having difficulty breathing, use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) if one is available. These inhaled medications dilate the airway.

• If you are feeling lightheaded or faint, lie down and raise your legs higher than your head to help blood flow to your brain.

• If you have been given an epinephrine kit for a previous allergic reaction, inject yourself as you have been instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms (see Follow-up).

• Bystanders should administer CPR to a person who becomes unconscious and stops breathing or does not have a pulse.

• If at all possible, you or your companion should be prepared to tell medical personnel what medications you take and your allergy history.

|Medical Treatment|

Like most allergic reactions, treatment is dictated by the severity of the reaction. Reactions that cover a large proportion of your body, make you uncomfortable enough to disrupt your normal activities, or do not get better within a few days may require treatment with prescription medications.

|Medications|

• Topical corticosteroid creams (prescription strength) - These reduce the immune response and relieve inflammatory symptoms.

• Oral corticosteroid medication (such as prednisone) - 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 3 days to as long as 4 weeks.

• Oral antihistamines - For itching. The main advantage of the prescription antihistamines is that they do not make you sleepy, allowing you to carry on your normal activities.

• Antibiotics - These are needed only if the skin becomes infected after the initial rash.

|Follow-up|

If you are treated by a medical professional, follow his or her recommendations exactly. Use all medications as directed.

Return to your health care provider if the symptoms do not begin to improve in 2 weeks.

|Prevention|

• Avoid these plants. Learn what they look like in your area. Be aware that their appearance can vary with the seasons.
  
  
• Do not burn the plants. Burning can release the allergens into the air.
  
  
• Wear proper clothing to protect your skin, such as gloves, long sleeves, and long pants.
  
  
• Bathe pets that may have the oil on their fur. Use soapy water. Do not forget to wear protective clothing while doing this.
  
  
• Wash any clothing that might contain the plant oil. Unwashed clothes can retain the oil and cause a rash in anyone who wears or handles them.
  
  
• Before you go out in a potentially infested area, you can apply nonprescription products such as Ivy Block or Stokoguard, which act as a barrier to the oils.
  
  
• Remember that the oil can be transferred from people, pets, or objects. Thoroughly wash anything that may carry the oil.

|Outlook|

The rash and itching usually get better gradually and go away completely in 2-3 weeks. Treatment should be continued at least this long because the rash can come back if medicines are stopped too soon. You may have temporary darkening of your skin when the rash disappears.

Surrounding redness, pain, and pus can indicate a skin infection, which your doctor can treat with antibiotics. This is more likely to happen if the rash is scratched so much that the skin is broken.

You almost certainly will have another reaction if you come in contact with these plants again after a first reaction.

|Web Links|

American Academy of Allergy, Asthma and Immunology (AAAAI)

allergic contact dermatitis, allergic reaction, poison ivy, poison oak, poison sumac, rhus (toxicodendron) dermatitis, type IV delayed hypersensitivity reaction, poison ivy allergic reaction, poison oak allergic reaction, poison sumac allergic reaction

Author: Daniel Jobe, MD, Consulting Staff, Department of Internal Medicine, Cornerstone Health Care.

Coauthor(s): Zoe Diana Draelos, MD, PA, Clinical Associate Professor, Department of Dermatology, Wake Forest University; Clinical Associate Professor, Department of Dermatology, Bowman Gray School of Medicine.

Editors: Patrick Taylor, MD, FAAEM, Medical Director, Department of Emergency Medicine, CHRISTUS St Frances Cabrini Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, ; James Ungar, MD, Medical Director, Chair Department of Emergency Medicine Santa Rosa Memorial Hospital.