From the Guidelines
Contact dermatitis occurs through two main mechanisms: irritant contact dermatitis and allergic contact dermatitis, with the latter being a delayed hypersensitivity reaction (type IV) that requires prior sensitization to an allergen, as described in the British Association of Dermatologists' guidelines for the management of contact dermatitis 2017 1. The mechanisms leading to contact dermatitis can be understood by considering the different types of reactions that occur in response to external agents.
- Irritant contact dermatitis results from direct damage to the skin by chemicals, detergents, solvents, or physical irritants that disrupt the skin barrier, causing inflammation without requiring prior sensitization and accounting for about 80% of cases.
- Allergic contact dermatitis, on the other hand, involves sensitization of the immune system to a specific allergen or allergens with resulting dermatitis or exacerbation of pre-existing dermatitis, as noted in the guidelines for the management of contact dermatitis: an update 1. When an allergen penetrates the skin, it binds to proteins and is processed by Langerhans cells, which present it to T lymphocytes, as discussed in the guidelines of care for the management of atopic dermatitis: section 4 1. Upon re-exposure, these sensitized T cells release inflammatory cytokines, causing the characteristic rash 24-72 hours later. Common allergens include nickel, fragrances, preservatives, rubber compounds, and plants like poison ivy, as identified in the British Association of Dermatologists' guidelines for the management of contact dermatitis 2017 1. The management of contact dermatitis should focus on identifying and avoiding the trigger, using topical corticosteroids, and maintaining skin hydration with moisturizers, as recommended in the British Association of Dermatologists' guidelines for the management of contact dermatitis 2017 1. For severe cases, oral corticosteroids like prednisone may be necessary, as noted in the guidelines for the management of contact dermatitis: an update 1. Understanding these mechanisms helps in proper diagnosis and management of contact dermatitis, and it is essential to consider the different types of reactions and the various allergens that can cause contact dermatitis, as discussed in the guidelines of care for the management of atopic dermatitis: section 4 1.
From the Research
Mechanisms of Contact Dermatitis
The mechanisms leading to contact dermatitis can be understood by examining the different forms of the condition and the immune responses involved.
- Irritant contact dermatitis is caused by direct contact with an exogenous substance, leading to skin inflammation through non-immune-modulated irritation of the skin 2.
- Allergic contact dermatitis, on the other hand, is a delayed hypersensitivity reaction that occurs after reexposure to a foreign substance, involving a T-cell-mediated immune response 3, 4, 5.
Immune Response
The immune response in allergic contact dermatitis involves several phases, including sensitization, elicitation, and resolution 5.
- During the sensitization phase, contact allergens are presented to antigen-presenting cells, which play a central role in the initiation of the immune response.
- The elicitation phase involves the activation of T-cells, which then migrate to the skin and cause inflammation.
- The resolution phase involves the production of anti-inflammatory cytokines and the down-regulation of the immune response by T-regulatory cells.
Key Players
Several types of immune cells are involved in the immune response to contact allergens, including:
- Antigen-presenting cells, such as Langerhans cells, which present contact allergens to T-cells 5.
- T-cells, including Th-1 and Th-17 cells, which are responsible for tissue damage and inflammation 5.
- Keratinocytes, which play a role in all phases of the immune response, from initiation to resolution 5.
Triggers
Common triggers for contact dermatitis include: