From the Guidelines
Allergic contact dermatitis is a type IV/delayed-type hypersensitivity reaction that occurs when small environmental chemicals, such as haptens or prehaptens, bind to epidermal carrier proteins and induce an inflammatory reaction on subsequent exposure. This reaction is mediated by the binding of these chemicals to proteins in the skin, forming complete antigens that are then processed by Langerhans cells and dendritic cells in the epidermis 1. The mechanism of allergic contact dermatitis involves two distinct phases: the sensitization phase, where the allergen penetrates the skin and binds to proteins, and the elicitation phase, where the previously sensitized memory T cells recognize the allergen and release inflammatory cytokines, recruiting additional inflammatory cells to the site.
The most common contact allergens in patients with atopic dermatitis include:
- Nickel
- Neomycin
- Fragrance
- Formaldehyde and other preservatives
- Lanolin
- Rubber chemicals These allergens can cause a range of symptoms, including redness, itching, swelling, and vesicle formation, typically appearing 24-72 hours after exposure 1. The diagnosis of allergic contact dermatitis is made through patch testing, where suspected allergens are placed on unaffected skin, typically the back, for 48 hours, and the presence of a reaction is assessed at the time of initial patch removal and again at a later time point, up to 7 days after application 1.
The key to managing allergic contact dermatitis is identifying and avoiding the triggering allergen, as well as using topical corticosteroids to reduce inflammation, and in severe cases, systemic treatments like oral corticosteroids or immunosuppressants may be necessary 1. It is essential to consider allergic contact dermatitis as a potential diagnosis in patients with atopic dermatitis, particularly those with unusual or atypical distributions of lesions, or those who do not respond to standard treatments 1.
From the Research
Mechanism of Allergic Contact Dermatitis
- Allergic contact dermatitis (ACD) is a T-cell-mediated skin inflammation resulting from the priming and expansion of allergen-specific CD4+ and CD8+ T cells 2.
- It is a delayed hypersensitivity reaction in which a foreign substance comes into contact with the skin; skin changes occur after reexposure to the substance 3.
- The clinical condition is characterized by local skin rash, itchiness, redness, swelling, and lesions, being mainly diagnosed by the patch test 2.
Causes and Triggers
- The most common substances that cause contact dermatitis include poison ivy, nickel, and fragrances 3.
- ACD can be triggered by various allergens, including topical corticosteroids, and systemic contact dermatitis can occur from prednisolone with tolerance of triamcinolone 4.
- Hypersensitivity reactions to corticosteroids are rare in the general population, but they are not uncommon in high-risk groups such as patients who receive repeated doses of CS 5.
Diagnosis and Treatment
- Contact dermatitis usually leads to erythema and scaling with visible borders, and itching and discomfort may also occur 3.
- Localized acute allergic contact dermatitis lesions are successfully treated with mid- or high-potency topical steroids, such as triamcinolone 0.1% or clobetasol 0.05% 3.
- If allergic contact dermatitis involves an extensive area of skin (greater than 20 percent), systemic steroid therapy is often required and offers relief within 12 to 24 hours 3.
- Patch tests and intradermal tests may be used to identify the causative allergen and to determine the safest alternative treatment 4, 6.