Poison oak is a plant which, similar to poison ivy and poison sumac, commonly causes a rash as a result of contact with a chemical which all three plants contain. The rash is caused by an allergic reaction that occurs in many people. It can cause severe itching and can be treated in a variety of ways.
Contact Dermatitis Mechanism
Poison oak typically causes problems by triggering allergic contact dermatitis. Allergies are caused by the immune system having a reaction to certain chemicals called allergens, the American Academy of Allergy Asthma and Immunology explains. The immune system makes proteins called antibodies which come in many different types. One kind of antibody, known as IgE antibodies, are responsible for generating allergic reactions. When these proteins bind to allergens, they recruit other immune cells, which secrete chemicals that cause nearby blood vessels to expand. This causes a rash to develop. Other chemicals can cause the skin to be itchy.
Poison Oak Allergen
The chemical which causes a poison oak allergy is called urushiol, according to the American Academy of Dermatology. This chemical is also responsible for irritation from poison ivy and poison sumac. This is a common allergen, although not all people are affected by it. People can become contaminated by urushiol by touching poison oak or by touching materials which have come into contact with poison oak. If poison oak is set on fire, the urushiol can become airborne and irritate the skin and the lining of the lungs.
Symptoms
A rash from poison oak will usually be red, slightly swollen, itchy and may develop blisters, the Mayo Clinic explains. If the rash is caused by direct contact with the plant, it often will be in a straight line from where the plant brushed against the skin. Cases of poison oak which are the result of wearing clothing that has become contaminated, on the other hand, will typically cause a more diffuse rash. Usually the rash will appear 12 to 48 hours after the contact with the plant and can last for up to eight weeks. The severity of the rash depends on the amount of urushiol that got on the skin.
Seeing a Doctor
In general, rashes caused by poison oak do not require medical attention--they rarely pose the risk of causing severe medical problems and will go away on their own. In some cases, the Mayo Clinic notes, medical attention may be needed, particularly if the rash is very severe or spread throughout the body. Cases of poison oak that affect the mouth, genitals or eyes may also need more intense care, as can cases of poison oak that cause blisters that ooze pus. Patients who develop a fever above 100 degrees F should also see a doctor.
Treatment
There are a number of treatments that can be used to ease the symptoms of poison oak. Lotions with corticosteroids or calamine can help ease the itching and inflammation. Many patients also benefit from taking oral antihistamines, including diphenhydramine. Cold-water compresses and oatmeal or baking soda baths can also help relieve the itching.
