Contact dermatitis is an inflammatory skin reaction that develops when the skin comes into contact with a substance that irritates it or triggers an allergic reaction.
The condition can cause itching, redness, swelling, burning, dryness, scaling and, in some cases, fluid-filled blisters. It commonly affects the hands and face but can occur anywhere on the skin.
There are two main forms of contact dermatitis: irritant and allergic.
Irritant contact dermatitis occurs when a substance damages or irritates the skin. Common triggers include soaps, detergents, bleach, solvents, disinfectants, fertilizers, pesticides and some personal-care products. Frequent exposure to water can also damage the skin’s protective barrier and contribute to the condition.
Allergic contact dermatitis occurs when the immune system reacts to a substance after a person has become sensitized to it. Common allergens include nickel, fragrances, some cosmetics and hair products, certain medicines and urushiol, the oil found in poison ivy, poison oak and poison sumac.
Poison ivy and urushiol
Poison ivy is a well-known cause of allergic contact dermatitis. Its rash is caused by urushiol, an oily resin found in the plant. Poison oak and poison sumac also contain urushiol.
Urushiol can reach the skin through direct contact with a plant or indirectly through contaminated clothing, tools, equipment or animal fur. The oil can remain capable of causing a reaction on contaminated objects for a long time if they are not properly cleaned.
A poison ivy rash commonly causes itching, redness, swelling and blisters. The reaction can appear within about 12 to 48 hours after exposure and may last two to three weeks.
The rash itself is not spread by scratching or by fluid from blisters. However, touching plant oil that remains on the skin, clothing or another contaminated object can transfer urushiol to another part of the body.
Burning poison ivy, poison oak or poison sumac can also expose people to urushiol in smoke and may cause serious irritation to the respiratory system.
Symptoms
Symptoms vary depending on the substance involved and whether the reaction is irritant or allergic.
People may develop an itchy rash, dry or cracked skin, swelling, burning or stinging, tenderness, blisters or oozing and crusting. The rash often appears on areas that have come into contact with the triggering substance, although allergic reactions can sometimes appear away from the original site of contact.
Symptoms may appear immediately or take hours or days to develop. This delay can make it difficult to identify the substance responsible, particularly when a person uses several skin, hair or cosmetic products.
Finding the cause
The most important step in managing contact dermatitis is identifying and avoiding the substance responsible.
A doctor or dermatologist may examine the rash and ask about a person’s work, hobbies, medicines, cosmetics, skin-care products and other substances that come into contact with the skin. If an allergic cause is suspected but cannot be identified, patch testing may be used.
Patch testing involves placing small amounts of potential allergens on the skin and checking for a delayed reaction. It can help identify substances responsible for recurring allergic contact dermatitis.
Treatment
Avoiding the irritant or allergen is the main treatment. When the cause can be identified and avoided, the skin can gradually clear.
For mild symptoms, cool wet compresses, moisturisers and some over-the-counter anti-itch treatments may help. Mayo Clinic lists 1% hydrocortisone cream, calamine lotion, cool compresses and oatmeal baths among options that may relieve symptoms in appropriate cases.
Doctors may prescribe topical corticosteroids when the skin is significantly inflamed. Severe or widespread cases may require medicines taken by mouth. The appropriate treatment depends on the cause, location and severity of the reaction.
People with recurring or unexplained rashes may need assessment by a dermatologist rather than repeatedly treating the symptoms without identifying the trigger.
There is limited evidence for complementary treatments and supplements for contact dermatitis, so they should not replace established treatment or avoidance of the trigger.
Preventing contact dermatitis
Prevention starts with avoiding substances known to cause a reaction.
People who regularly work with irritants or allergens can reduce exposure by using appropriate protective clothing and gloves. Mild, fragrance-free cleansers and regular moisturising can also help protect the skin barrier, particularly for people whose hands are frequently exposed to water or chemicals.
If poison ivy, poison oak or poison sumac is suspected, exposed skin should be washed with soap and water as soon as possible. Clothing, tools and other objects that may have come into contact with the plant oil should also be cleaned.
People should also avoid scratching the rash because repeated scratching can damage the skin and increase the risk of infection.
When to seek medical care
Medical attention may be necessary when a rash is severe, widespread or persistent, or when it affects sensitive areas such as the eyes, mouth, face or genitals.
A person should also seek medical care if the skin becomes increasingly painful, develops pus or is accompanied by a fever, as these can indicate an infection.
Difficulty breathing after exposure to smoke from poison ivy or another poisonous plant requires immediate medical attention.
Contact dermatitis is usually manageable, but identifying the substance responsible is important. For people with recurring reactions, professional assessment can help identify the trigger and reduce further exposure.
