Contact dermatitis is a red, itchy rash caused by direct contact with a substance or an allergic reaction to it. The rash isn't contagious or life-threatening, but it can be very uncomfortable.

Many substances can cause such reactions, including soaps, cosmetics, fragrances, jewelry and plants.

To treat contact dermatitis successfully, you need to identify and avoid the cause of your reaction. If you can avoid the offending substance, the rash usually clears up in two to four weeks. You can try soothing your skin with cool, wet compresses, anti-itch creams and other self-care steps.

Contact dermatitis usually occurs on areas of your body that have been directly exposed to the reaction-causing substance — for example, along a calf that brushed against poison ivy or under a watchband. The rash usually develops within minutes to hours of exposure and can last two to four weeks.

Signs and symptoms of contact dermatitis include:

• A red rash
• Itching, which may be severe
• Dry, cracked, scaly skin
• Bumps and blisters, sometimes with oozing and crusting
• Swelling, burning or tenderness

When to see a doctor

See your doctor if:

• The rash is so uncomfortable that you are losing sleep or are distracted from your daily activities
• The rash is sudden, painful, severe or widespread
• You're embarrassed by the way your skin looks
• The rash doesn't get better within three weeks
• The rash affects your face or genitals

Seek immediate medical care in the following situations:

• You think your skin is infected. Clues include fever and pus oozing from blisters.
• Your lungs, eyes or nasal passages are painful and inflamed, perhaps from inhaling an allergen.
• You think the rash has damaged the mucous lining of your mouth and digestive tract.

Contact dermatitis is caused by a substance you're exposed to that irritates your skin or triggers an allergic reaction. The substance could be one of thousands of known allergens and irritants. Some of these substances may cause both irritant contact dermatitis and allergic contact dermatitis.

Irritant contact dermatitis is the most common type. This nonallergic skin reaction occurs when a substance damages your skin's outer protective layer.

Some people react to strong irritants after a single exposure. Others may develop signs and symptoms after repeated exposures to even mild irritants. And some people develop a tolerance to the substance over time.

Common irritants include:

• Solvents
• Rubbing alcohol
• Bleach and detergents
• Shampoos, permanent wave solutions
• Airborne substances, such as sawdust or wool dust
• Plants
• Fertilizers and pesticides

Allergic contact dermatitis occurs when a substance to which you're sensitive (allergen) triggers an immune reaction in your skin. It usually affects only the area that came into contact with the allergen. But it may be triggered by something that enters your body through foods, flavorings, medicine, or medical or dental procedures (systemic contact dermatitis).

You may become sensitized to a strong allergen such as poison ivy after a single exposure. Weaker allergens may require multiple exposures over several years to trigger an allergy. Once you develop an allergy to a substance, even a small amount of it can cause a reaction.

Common allergens include:

• Nickel, which is used in jewelry, buckles and many other items
• Medications, such as antibiotic creams and oral antihistamines
• Balsam of Peru, which is used in many products, such as perfumes, cosmetics, mouth rinses and flavorings
• Formaldehyde, which is in preservatives, disinfectants and clothing
• Personal care products, such as deodorants, body washes, hair dyes, cosmetics and nail polish
• Plants such as poison ivy and mango, which contain a highly allergenic substance called urushiol
• Airborne substances, such as ragweed pollen and spray insecticides
• Products that cause a reaction when you're in the sun (photoallergic contact dermatitis), such as some sunscreens and oral medications

Children develop the condition from the usual offenders and also from exposure to diapers, baby wipes, sunscreens, clothing with snaps or dyes, and so on.

Some jobs and hobbies put you at higher risk of contact dermatitis. Examples include:

• Health care and dental employees
• Metalworkers
• Construction workers
• Hairdressers and cosmetologists
• Auto mechanics
• Scuba divers or swimmers, due to the rubber in face masks or goggles
• Cleaners
• Gardeners and agricultural workers
• Cooks and others who work with food

Contact dermatitis can lead to an infection if you repeatedly scratch the affected area, causing it to become wet and oozing. This creates a good place for bacteria or fungi to grow and may cause an infection.

General prevention steps include the following:

• Avoid irritants and allergens. Try to identify and avoid substances that irritate your skin or cause an allergic reaction.
• Wash your skin. You might be able to remove most of the rash-causing substance if you wash your skin right away after coming into contact with it. Use a mild, fragrance-free soap and warm water. Rinse completely. Also wash any clothing or other items that may have come into contact with a plant allergen, such as poison ivy.
• Wear protective clothing or gloves. Face masks, goggles, gloves and other protective items can shield you from irritating substances, including household cleansers.
• Apply an iron-on patch to cover metal fasteners next to your skin. This can help you avoid a reaction to jean snaps, for example.
• Apply a barrier cream or gel. These products can provide a protective layer for your skin. For example, an over-the-counter skin cream containing bentoquatam (IvyBlock) may prevent or lessen your skin's reaction to poison ivy.
• Use moisturizer. Regularly applying moisturizing lotions can help restore your skin's outermost layer and keep your skin supple.
• Take care around pets. Allergens from plants, such as poison ivy, can cling to pets and then be spread to people.

Your doctor may be able to diagnose contact dermatitis and identify its cause by talking to you about your signs and symptoms, questioning you to uncover clues about the trigger substance, and examining your skin to note the pattern and intensity of your rash.

Your doctor may recommend a patch test to see if you're allergic to something. This test can be useful if the cause of your rash isn't apparent or if your rash recurs often.

During a patch test, small amounts of potential allergens are applied to adhesive patches, which are then placed on your skin. The patches remain on your skin for two to three days, during which time you'll need to keep your back dry.

Your doctor then checks for skin reactions under the patches and determines whether further testing is needed.

If home care steps don't ease your signs and symptoms, your doctor may prescribe medications. Examples include:

• Steroid creams or ointments. These topically applied creams or ointments help soothe the rash of contact dermatitis. A topical steroid may be applied one or two times a day for two to four weeks.
• Oral medications. In severe cases, your doctor may prescribe oral corticosteroids to reduce inflammation, antihistamines to relieve itching or antibiotics to fight a bacterial infection.

To help reduce itching and soothe inflamed skin, try these self-care approaches:

• Avoid the irritant or allergen. The key to this is identifying what's causing your rash and staying away from it. Your doctor may give you a list of products that typically contain the substance that affects you. Also ask for a list of products that are free of the substance that affects you.

  If you're allergic to the metal in a piece of jewelry, you may be able to wear it by putting a barrier between you and the metal. For example, line the inside of a bracelet with a piece of clear tape or paint it with clear nail polish.

• Apply an anti-itch cream or lotion to the affected area. A nonprescription cream containing at least 1 percent hydrocortisone can temporarily relieve your itch. A steroid ointment may be applied one or two times a day for two to four weeks. Or try calamine lotion.
• Take an oral anti-itch drug. A nonprescription oral corticosteroid or antihistamine, such as diphenhydramine (Benadryl), may be helpful if your itching is severe.
• Apply cool, wet compresses. Moisten soft washcloths and hold them against the rash to soothe your skin for 15 to 30 minutes. Repeat several times a day.
• Avoid scratching. Trim your nails. If you can't keep from scratching an itchy area, cover it with a dressing.
• Soak in a comfortably cool bath. Sprinkle the water with baking soda or an oatmeal-based bath product.
• Protect your hands. Rinse and dry hands well and gently after washing. Use moisturizers throughout the day. And choose gloves based on what you're protecting your hands from. For example, plastic gloves lined with cotton are good if your hands are often wet.

You're likely to start by seeing your primary care doctor. He or she might refer you to a doctor who specializes in skin disorders (dermatologist).

Because appointments can be brief, it's a good idea to be well-prepared for your appointment.

What you can do

• List your signs and symptoms, including when they began and how long they've lasted.
• Avoid any substances that you think may have caused the rash.
• Make notes about any new products you've started using and any substances that regularly come in contact with your affected skin areas.
• Make a list of all the medications and supplements you take. Even better, take along the original bottles and a list of the dosages and directions. Include any creams or lotions you're using.
• List questions to ask your doctor.

For contact dermatitis, some basic questions you could ask your doctor include:

• What might be causing my signs and symptoms?
• Are tests needed to confirm the diagnosis?
• What treatments are available, and which do you recommend?
• Is this condition temporary or chronic?
• Can I wait to see if the condition goes away on its own?
• Will scratching spread the rash?
• Will popping the blisters spread the rash?
• What skin care routines do you recommend to improve my condition?
• How can I prevent this in the future?

What to expect from your doctor

Your doctor is likely to ask you questions such as the following:

• When did you begin noticing symptoms?
• How often do you have symptoms?
• Have your symptoms been continuous or occasional? Do they get better over the weekend or during vacation?
• Does anything seem to make your symptoms better or worse?
• Have you started using any new soaps, lotions, cosmetics or household products?
• Does your work or a hobby involve using products that often come in contact with your skin?