Allergic contact dermatitis
Allergic contact dermatitis (ACD) is a form of eczema that occurs when the skin comes into contact with a substance to which it has developed an allergic reaction. This condition is characterized by a delayed hypersensitivity reaction, which is mediated by the immune system. Unlike irritant contact dermatitis, which can occur immediately upon exposure to a harsh substance, allergic contact dermatitis typically develops over time, as the immune system becomes sensitized to a particular allergen.
The pathophysiology of ACD involves a two-phase process: sensitization and elicitation. During the sensitization phase, the skin is exposed to an allergen, which is a small molecule that can penetrate the skin barrier. This allergen binds to skin proteins, forming a complex that is recognized as foreign by Langerhans cells, a type of antigen-presenting cell in the skin. These cells process the allergen and migrate to the lymph nodes, where they present it to T-lymphocytes, a type of white blood cell. This process primes the immune system to recognize the allergen as a threat.
Upon subsequent exposure to the same allergen, the elicitation phase occurs. The previously sensitized T-lymphocytes recognize the allergen and release inflammatory cytokines, leading to an immune response that manifests as the symptoms of dermatitis. These symptoms typically include redness, swelling, itching, and the formation of blisters or vesicles on the skin. The affected area may also become dry, cracked, and scaly over time.
Common allergens that can cause allergic contact dermatitis include nickel, found in jewelry and metal fastenings; fragrances and preservatives in cosmetics and personal care products; rubber compounds in latex gloves; and certain plants, such as poison ivy, poison oak, and poison sumac. The diagnosis of ACD is often confirmed through patch testing, where small amounts of potential allergens are applied to the skin under occlusive patches to observe for a reaction.
Management of allergic contact dermatitis involves identifying and avoiding the offending allergen. Topical corticosteroids are commonly used to reduce inflammation and alleviate symptoms. In more severe cases, systemic corticosteroids or other immunosuppressive agents may be necessary. Patient education is crucial, as understanding the sources of allergens and how to avoid them can significantly reduce the incidence of flare-ups.
In summary, allergic contact dermatitis is a common skin condition resulting from an allergic reaction to specific substances. It involves a complex immune response and requires careful management to prevent and treat outbreaks. Understanding the triggers and maintaining good skin care practices are essential components of managing this condition effectively.
| Allergic contact dermatitis | |
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| Illustration of allergic contact dermatitis | |
| Specialty | Dermatology, immunology |
Allergic contact dermatitis (ACD) is a form of contact dermatitis that is the manifestation of a type IV hypersensitivity (delayed hypersensitivity) response caused by contact with a substance; the other type being irritant contact dermatitis (ICD). It differs from classical allergic reactions, which are type I hypersensitivity reactions.
Although less common than ICD, ACD is accepted to be the most prevalent form of immunotoxicity found in humans. By its hypersensitive nature, this form of contact dermatitis is atypical within the population. The mechanisms by which these reactions occur are complex, with many levels of fine control. Their immunology centres on the interaction of immunoregulatory cytokines and discrete subpopulations of T lymphocytes.