Poison oak allergy
Rash from urushiol in poison oak.
About poison oak allergy
Poison oak produces an itchy, blistering rash caused by urushiol, the same oily resin responsible for poison ivy. Urushiol triggers a delayed, type IV allergic contact dermatitis, so the reaction generally appears 12 to 72 hours after skin contact rather than immediately. Poison oak is native to North America, so within the UK it is mainly a concern for travellers and for people handling the plant in specialist gardens or nurseries. The resin clings tenaciously to skin, clothing, tools and pet fur, and can be carried some distance from the plant itself.
The rash is red, very itchy and typically blistered, often appearing in streaks or patches where the leaves brushed the skin, most commonly on exposed areas such as the arms, legs, hands and face. It may seem to develop over several days as more lightly exposed skin reacts later, but the blister fluid does not spread it. Contaminated items can cause repeated outbreaks until thoroughly washed. Because the trigger is urushiol, people who react to poison oak also react to poison ivy and poison sumac, and may cross-react with mango and cashew.
Diagnosis is usually clinical, from the appearance and a history of plant contact, and patch testing is seldom required. Management is prompt washing of skin and contaminated objects, avoidance, and relief with cool compresses, emollients and antihistamines. See your GP if the rash is extensive, affects the face or genitals, or is severe, as prescription steroid treatment may be needed.
Common triggers
- Poison oak and products containing it
Symptoms
- Red, itchy rash (contact dermatitis)
- Dry, cracked or scaly skin
- Blistering or weeping in severe cases
- Burning or stinging where skin met the trigger
Avoidance & management
- Avoid skin contact with the trigger
- Wear gloves or use barrier creams
- Choose products labelled free from the allergen
- Rinse skin promptly after contact
- Use emollients or prescribed steroid creams
Sources & references
Allergy safety: what everyone should know
Mild-to-moderate reaction signs
- Itching, hives or a raised rash
- Swelling of lips, face or eyes
- Tingling mouth, sneezing, runny nose
- Stomach pain, nausea or vomiting
Anaphylaxis — call 999 (UK) or 112 (EU) immediately
- Difficult or noisy breathing, wheeze, persistent cough
- Swelling of the tongue or tightness in the throat
- Dizziness, collapse, pale and floppy (young children)
- Use an adrenaline auto-injector (e.g. EpiPen) at once if prescribed, then call an ambulance even if symptoms improve
Allergy or intolerance? A true allergy involves the immune system and can escalate quickly; an intolerance (e.g. lactose intolerance) is unpleasant but not life-threatening. The symptoms overlap, so self-diagnosis is unreliable.
Getting tested: home-testing kits based on IgG are not diagnostically valid. If you suspect an allergy, ask a GP for referral to an allergy clinic for skin-prick or specific-IgE testing and a supervised food challenge where appropriate.