POISON OAK (Contact Dermatitis)
Description
Poison oak is known as an allergic contact dermatitis. About 70% of adults who contact poison oak
or poison ivy will develop a rash in a delayed fashion from about 8 hours minimum to as much as 2
weeks later. The rash is due to an allergic reaction to urushiol resin on leaves or stems. Exposure
to poison oak resin via contact with contaminated clothing, smoke, or animals with the resin on
their fur can also cause the rash.
Signs and Symptoms
Poison oak causes major itching. The rash depends on the extent of exposure. Mild exposures
lead to mild redness. The face, wrists and genitals are frequently involved because thin skin is
more susceptible to contact allergy. More intense exposures result in blisters and uncomfortable
swelling or edema. Linear blisters or bumps are highly suggestive of poison oak. Without treatment
the rash usually builds to a maximum over a few days to a week. The fluid from a weeping poison
oak rash does not spread the rash and is not contagious.
Treatment
Prevention works best. A product called Ivy Block provides an effective barrier against urushiol if
you are going hiking or doing yard work. Try to wash with soap and water within 15 minutes after
any potential exposure to poison oak or poison ivy (East Coast). There is no approved safe oral
desensitizing medicine.
Clothes that might be contaminated with the allergic resin should be washed with soap and water.
If the rash is weeping, then cool wet compresses applied for 15 minutes several times a day will
lead to rapid drying and relief. Shake lotions like Calamine, Caladryl, and Tech-nu provide relief in
mild cases.
More intense cases require prescription steroid medication. Steroid creams will reduce itching and
shorten the course if the rash is limited. Oral steroids in the form of Prednisone or an injection of
Triamcinolone are used to treat poison oak which involves large surface areas, the face, eyelids
and/or genitals. Oral steroids work within 48 hrs to reduce the spread and intensity of the rash.
Systemic steroids (oral or injected forms) may have significant side effects so there should be
reasonable justification.
Reviewed 1/11/2011
R Molino, MD
Student Health Service