http://www.skincarephysicians.com/eczemanet/contact_dermatitis.html American Academy of Dermatology
Signs and Symptoms
Allergic contact dermatitis usually develops a few hours after the allergen (substance to which the person is allergic) touches the skin and causes:
Itchy, swollen, and red skin or dry and bumpy skin
Blisters may develop if the reaction is more severe
Blisters may break, leaving crusts and scales
Skin may later flake and crack
With long-term exposure to an allergen, the skin becomes thick, red, and scaly. Over time, the skin can darken and become leathery.
Irritant contact dermatitis occurs after frequent exposure to a mild irritant, such as detergent, and after brief exposure to a strong irritant, such as battery acid. Signs and symptoms of irritant contact dermatitis include:
Mild irritant – Begins with dry, chapped skin. With repeat exposure, patches of itchy, red, scaly, and swollen skin develop. The skin may burn or sting upon contact. If exposure continues, the skin tends to crack, scale, and become excessive dry. Sores and blisters may develop that later erupt, forming crusts and scales.
Strong irritant – Upon contact, the skin may burn, sting, and/or itch. Redness, swelling, blistering usually develop. Later, scale may form.
Once irritant contact dermatitis develops, exposure to mild substances, such as baby shampoo and even water, can irritate the skin and make the condition worse.
Anyone can develop irritant contact dermatitis with sufficient exposure to something that damages the skin and causes irritation.
Allergic contact dermatitis occurs when someone develops an allergy to a something that touches the skin.
Allergic contact dermatitis. More than 3,000 allergens (substance to which the person is allergic) are known to cause allergic contact dermatitis. Common allergens include:
Antibiotic ointment. Ingredients in over-the-counter topical antibiotic ointments frequently cause an allergic skin reaction.
Clothing and shoes. The leather, glue, or rubber in one’s shoes can cause allergic contact dermatitis as can dyes and fire retardants used in clothing.
Concrete. Often the cause of chronic hand dermatitis, a reaction to concrete can persist long after the exposure ends.
Fragrances. Found in perfumes, makeup, as well as skin and hair care products, fragrances commonly cause an allergic reaction. Even products labeled “unscented” can cause a reaction because unscented does not mean the product does not contain fragrance; it means the fragrance is masked. Look for products labeled “fragrance free.”
Metals. Metals occur in everyday objects that we touch and in our food. Nickel, one of the most common metals that causes an allergic reaction, is found in jewelry and many foods, including tomatoes, chocolate, nuts, and soy. Mercury (used in dental fillings), gold, cobalt, and chromate (used to tan leather) are other metals that frequently cause allergic contact dermatitis.
Plants. A brush with poison ivy, poison oak, or poison sumac is a frequent cause.
Rubber accelerators. Found in everything from mouse pads to gym equipment, these allergens can be difficult to find.
Sometimes allergic contact dermatitis does not flare until it is triggered. Ultraviolet (UV) light and perspiration can trigger allergic contact dermatitis.
Exposure to ultraviolet (UV) light. The rash may not develop until triggered by exposure to sunlight or another source of UV light, such as a tanning bed. Called photoallergy, this form of allergic contact dermatitis occurs when an everyday product, such as a fragrance or sunscreen, is applied to the skin and then exposed to UV light. Some medications also can cause a photoallergic reaction.
Perspiration. This may trigger a flare-up. For example, some people who develop an allergy to nickel may not have a flare-up when nickel touches their skin unless they perspire.
Irritant contact dermatitis. When a substance damages the skin faster than the skin can repair itself, irritant contact dermatitis develops. Substances that frequently cause irritant contact dermatitis include water, soaps, detergents, cleaners, fiberglass, hair dyes, solvents, oils, paints, varnishes, foods, and metalworking fluids.
Medical history. While anyone can develop irritant contact dermatitis, having a history of atopic dermatitis, allergic contact dermatitis, or psoriasis increases the risk. Pre-existing hand dermatitis also increases the risk.
Age. Younger individuals are more susceptible to allergic contact dermatitis because the immune system of a younger person is more likely to overreact than the immune system of an older person.
Repeat exposure. The first exposure does not always result in an outbreak. With allergic contact dermatitis, the person’s skin often touches the allergen for many years before a reaction develops. Mild irritants, such as detergent, fish scales, and garlic, require frequent exposure to cause irritant contact dermatitis.
Occupation. People who work in certain occupations have a much higher risk of developing contact dermatitis. Health care workers, hairdressers, people who handle food, bartenders, janitors, and mechanics — to name a few — have an increased risk.
Gender. Females tend to have a slightly higher risk of developing contact dermatitis.
Environment. Extreme heat and cold as well as very humid and very dry environments increase the risk.
When the responsible allergen or irritant no longer touches the skin, the skin can clear. If the responsible substance(s) continues to touch the skin, contact dermatitis can become severe and difficult to treat.
Diagnosis begins with a complete medical history and examination of the skin.
If the dermatologist suspects allergic contact dermatitis, a safe and effective test called patch testing can help identify the allergen(s). During a patch test, strips of tape that contain small amounts of several possible allergens, usually 25 to 150, are applied to the patient’s back. The amounts are too small to cause a reaction unless the person is allergic. After 2 days, the patient returns, and the tape is removed. If a small red spot appears, the substance is considered a possible allergen. After 96 hours, the patient is checked again to see if any delayed reactions occur.
Irritants cannot be identified via testing. To identify irritants, a dermatologist must ask questions.
Avoiding the substance(s) causing the irritation or allergy. The patient must avoid the cause. Avoiding all substances that can trigger a flare-up can be difficult — if not impossible — when the person encounters these substances in the workplace. Dermatologists usually help their patients develop a strategy to circumvent exposure. This may include using a barrier cream, wearing gloves, and practicing glove hygiene.
Therapy to help clear the skin. Treatment may include applying emollients and moisturizers frequently throughout the day, taking an oral antihistamine to help stop the itch, and applying a topical corticosteroid or calcineurin inhibitor to reduce inflammation. In more severe cases, phototherapy treatments may be used to suppress the person’s overactive immune response. If an infection develops, antibiotics are necessary.
If contact dermatitis persists despite treatment, oral or injectable corticosteroids can be used for a short time to get the inflammation under control.
Once the contact dermatitis clears, the patient must continue to avoid the identified allergens — and sometimes irritants. For example, patients who develop an allergic reaction when nickel touches their skin need to avoid jewelry that contains nickel as well as many foods, including canned goods, tomatoes, and chocolate. A dermatologist can help the patient devise a strategy for avoiding known allergens.
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