Dermatitis is an inflammation of the skin. Contact dermatitis is a localized rash or irritation of the skin caused by direct contact with the inducing substance to which the skin reacts. Such substances are toxic to the skin and are called primary irritants. Others can trigger an immunological response called allergic contact dermatitis and include vegetable oils, metals, detergents, cosmetic additives, perfumes, industrial chemicals, topical antibiotics, and latex rubber additives.
What are the causes of contact dermatitis?
There are two types of contact dermatitis: allergic and irritant. They can often appear visually identical.
- Allergic contact dermatitis often results from an immune response to a small, structurally simple molecule.
- To become allergic to such a substance, one must have had at least one previous exposure that eventually induces an immune response.
- This dermatitis is not caused by an antibody, but results from a cellular immune response mediated by a type of blood cell (T lymphocytes) with surface molecules that allow the recognition of specific chemical allergens.
- When these lymphocytes come in contact with the allergen, they release a variety of chemicals that can cause itchy dermatitis.
- Usually this type of reaction only happens on the skin and takes at least 24 to 48 hours to develop.
- Common plants that produce allergic contact dermatitis include poison ivy, poison oak, and poison sumac. The allergenic chemical is present in the oil or latex that covers stems or leaves.
- Many other substances can cause allergic reactions, including ingredients of hair dyes or hair straighteners; metallic nickel in jewelry and buckles; leather tanning agents; and chemical additives for latex rubber.
- The fragrances in soap and preservatives and emulsifiers in shampoos, lotions, perfumes and cosmetics can cause reactions.
- Medications applied to the skin, such as neomycin (Neosporin, Neo-Fradin, Neo-Tab), are a common cause of this type of dermatitis.
- Irritant contact dermatitis occurs when you come into contact with a substance that is directly toxic to your skin. No allergy is needed and it will occur with the first exposure.
- The longer the substance remains on the skin, the more severe the reaction.
- Many chemicals, including industrial cleaning products and solvents, can cause this condition.
- Household cleaners such as detergents can also cause dermatitis.
- People with other skin conditions, such as eczema (atopic dermatitis), are more likely to have contact dermatitis.
What are Contact Dermatitis Risk Factors?
Exposure to normal or damaged skin to irritating chemical or known allergens is a significant risk. Anyone who compulsively washes their hands many times a day can develop a dermatitis caused by soap and water. Common solvents used in the workplace can damage the skin, cause irritant dermatitis and give allergens access to the deeper tissues. It is known that the use of ear piercing predisposes to nickel allergy. The use of topical antibiotics such as neomycin is associated with an allergy to this antibiotic.
Is contact dermatitis contagious?
Contact dermatitis is not caused by an infectious microorganism and is not contagious. Because the condition can produce open, rough skin, a secondary infection can develop on damaged skin. This secondary infection can be contagious.
What are signs and symptoms of contact dermatitis?
Distinguishing allergic contact dermatitis from irritant contact dermatitis and other forms of dermatitis can be challenging. A full history and physical exam are often necessary.
- A red rash is the usual response. It immediately appears in irritant contact dermatitis, but in allergic contact dermatitis, the rash does not appear one to two days after exposure.
- Your skin can develop small fluid-filled structures (vesicles) that can cause crying, a feature of this type of eruption. This condition is distinguished from hives (urticaria) that produce short-term itchy welts (wheals).
- Hives are usually caused by allergic reactions to food and medicines taken orally, but local contact hives occur and are mediated by antibodies.
- Your skin will itch and maybe burn. Irritant contact dermatitis can be more painful than itching.
- Irritant contact dermatitis often affects the hands, which are exposed by resting or immersing in a container (sink, bucket, tub) containing the irritant.
- Once a response starts, it can take four weeks to fully resolve.
