Poison ivy rash: what it is, symptoms and treatment

Poison ivy, poison oak and poison sumac are plants that carry an oil called urushiol on their surfaces. When the oil touches the skin it often causes an itchy, blistering rash. This is the information given by the American Academy of Dermatology (AAD), a US body. UK health sources do not discuss poison ivy by name, so the UK guidance on allergic contact dermatitis, which is the type of rash involved, is used alongside it on this page.

The NHS explains that contact dermatitis is a type of eczema triggered by contact with a particular substance. It can be caused by an irritant, which directly damages the outer layer of skin, or by an allergen, which makes the immune system respond in a way that affects the skin. A reaction to a plant oil is an allergic one.

NICE Clinical Knowledge Summaries explain that allergic contact dermatitis is a type IV (delayed) hypersensitivity reaction that occurs after sensitisation and subsequent re-exposure to a specific allergen, and that certain plants, such as sunflower and primula, are among the allergens that can cause it. The British Association of Dermatologists adds that once the skin becomes sensitive to an allergen, inflammation will happen whenever it comes into further contact.

The AAD describes an itchy, blistering rash. The NHS says contact dermatitis causes the skin to become itchy, blistered, dry and cracked. Lighter skin can become red, and darker skin can become dark brown, purple or grey. It can affect any part of the body, but most commonly the hands and face.

The British Association of Dermatologists says allergic contact dermatitis usually starts as an itchy rash that looks red, inflamed and blistered, and that the affected skin can peel and look red and oozy. In richly pigmented skin it can look purple, deep brown or greyish.

NICE says acute contact dermatitis typically presents with redness and small fluid-filled blisters (vesiculation), and that dryness, scaling and larger blisters may also be present.

The AAD says most people can safely treat the rash at home if it is mild, covers a small area and they are certain that poison ivy, poison oak or poison sumac caused it. Its advice has two parts: removing the oil, then relieving the itch.

• Immediately wash your skin with warm, soapy water, rubbing alcohol or dish soap. If you do this straight after touching the plant, you may wash off some of the oil and help prevent spreading it to other areas or other people.

• Put on gloves, remove your clothing and wash everything you were wearing in a washing machine. The oil can stick to clothing, gardening tools, leashes and pets’ fur, and can cause a further rash if it touches your skin.

• Do not scratch, because scratching can cause an infection. Leave blisters alone, and if they open do not remove the overlying skin.

• Apply cool compresses, and use calamine lotion or hydrocortisone cream to ease the itch.

• Take short, warm baths with colloidal oatmeal or baking soda added, or short cool showers.

• Consider antihistamine tablets. The AAD advises against applying an antihistamine to the skin, because it can worsen the rash and the itch.

The NHS says that if you come into contact with an allergen or irritant you should rinse the affected skin with warm water and an emollient as soon as possible. A pharmacist can recommend emollients (moisturisers) and the NHS says you should speak to one if your contact dermatitis is troubling you.

If your skin is sore and inflamed a GP may prescribe a topical corticosteroid (a cream or ointment). The NHS says it will usually start to have an effect within a few days, and that you should apply the emollient first and wait around 30 minutes before applying the steroid. In a severe episode that covers a large area of skin, a doctor may prescribe corticosteroid tablets, but the NHS says this is rarely needed.

NICE Clinical Knowledge Summaries list the treatment of acute contact dermatitis as avoiding the stimulus, liberal application of an emollient, consideration of topical corticosteroids depending on the clinical situation, and treatment of any secondary skin infection. The British Association of Dermatologists adds that cool compresses or oatmeal baths may help soothe sudden flare-ups.

None of the UK sources used here gives a duration for poison ivy specifically, and the AAD page does not give one. What UK sources say about allergic contact dermatitis in general is that the course depends on the cause and on being able to avoid further exposure. The NHS says that if the substance causing it can be identified and avoided, symptoms should improve and may even clear up completely.

The British Association of Dermatologists says it may take several months for contact dermatitis to settle, and that continued contact with the trigger will make it worse. If a rash is not settling, is spreading or keeps coming back, see a GP.

The British Association of Dermatologists says contact dermatitis is not contagious and cannot spread from person to person. The rash does not pass from one person to another through touching the blisters.

What can spread is the oil. The AAD says it can stick to clothing, tools and pet fur, and that you should wear gloves when handling or washing these. The British Association of Dermatologists also warns that bacterial infection of contact dermatitis can lead to impetigo, which is very contagious and needs treatment from a healthcare provider.

The AAD says to go to the emergency room immediately if you have any of the following, as these are signs of a severe reaction that requires immediate medical care. In the UK, call 999 or go to A&E.

• Difficulty breathing or swallowing.

• A rash around one or both eyes, your mouth, or on your genitals.

• Swelling on your face, especially if an eye has swollen shut.

• Itching that worsens or makes it impossible to sleep.

• A rash on most of your body.

• A fever.

The NHS says to see a GP if you have persistent, recurrent or severe symptoms of contact dermatitis. A GP may refer you to a dermatologist if the substance cannot be identified or your symptoms are not responding to treatment. NICE says referral should be considered for severe, chronic or recurrent dermatitis, especially of the hands and face, or if the rash looks atypical or is not responding to measures in primary care.

The AAD says to see a dermatologist if the rash appears on multiple areas of the skin, is severe (blisters, swelling and intense itching), may be infected (redness, pain, pus or draining), might be poison ivy but you are unsure, or is your first time getting such a rash.

NICE lists conditions that can be mistaken for contact dermatitis, including atopic or seborrhoeic dermatitis, skin infections such as cellulitis, impetigo and fungal infections, and other skin conditions such as urticaria (hives) and psoriasis. This is one reason an unclear rash should be looked at by a clinician.

On the NHS the first stop for a mild rash is a pharmacist, then a GP if it is persistent, severe or spreading. The NHS says a GP may refer you to a dermatologist. Patch testing, which the British Association of Dermatologists says is done in a specialist dermatology department to identify the exact cause of allergic contact dermatitis, is usually kept for cases where the cause is unknown or the rash is not responding to treatment.

Private dermatology services offer similar assessments and patch testing, often with shorter waits. If you were exposed to the plant on a trip abroad, tell the clinician where and when, because it helps with the diagnosis.