Poison sumac allergy
Rash from urushiol in poison sumac.
About poison sumac allergy
Poison sumac causes an itchy, blistering rash through urushiol, the same resin found in poison ivy and poison oak. As with those plants, the reaction is a delayed, type IV allergic contact dermatitis, appearing around 12 to 72 hours after contact rather than straight away. Poison sumac grows in wet, wooded areas of North America, so it is chiefly a risk for travellers and for those working with imported specimens rather than a common UK plant. Its urushiol is potent and, like the others, sticks readily to skin, clothing, tools and animal fur.
The rash is red, intensely itchy and often blistered, forming streaks or patches where the plant contacted the skin, usually on exposed areas such as the arms, legs and hands. It may appear to spread over several days as different areas react at different rates, but the fluid within the blisters is not itself infectious or spreading. Fresh outbreaks can occur from contaminated items until they are washed. Because the culprit is urushiol, anyone allergic to poison sumac will also react to poison ivy and poison oak, and may cross-react with mango skin and cashew shells.
Diagnosis is generally clinical, based on the rash and history of exposure, with patch testing rarely needed. Management involves washing skin and contaminated objects quickly, avoiding the plant, and relieving symptoms with cool compresses, emollients and antihistamines. See your GP if the rash is widespread, involves the face or genitals, or is severe, when stronger steroid treatment may be required.
Common triggers
- Poison sumac 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.