Allergic Contact Dermatitis: Hypersensitivity Type

Allergic contact dermatitis is a type of immune response where the skin reacts to an allergen after prior sensitization. This reaction is characterized by its delayed onset.

Contact Dermatitis Mechanism

This specific skin reaction involves the immune system's T-cells. Upon re-exposure to an allergen (like poison ivy or nickel), sensitized T-cells become activated, leading to inflammation and visible skin changes.

Hypersensitivity Classification

Immune reactions are classified into different hypersensitivity types:

• Type 1: Immediate reactions (e.g., hay fever, anaphylaxis). Mediated by IgE antibodies.
• Type 2: Cytotoxic reactions (e.g., autoimmune hemolytic anemia). Mediated by IgG or IgM antibodies.
• Type 3: Immune complex reactions (e.g., serum sickness). Mediated by antigen-antibody complexes.
• Type 4: Delayed-type hypersensitivity (DTH). Mediated by T-cells.

Dermatitis and Type 4 Hypersensitivity

Allergic contact dermatitis fits the definition of Type 4 hypersensitivity because it is a T-cell mediated response that typically manifests 24-72 hours after exposure to the allergen. This delayed reaction distinguishes it from other hypersensitivity types.

Therefore, allergic contact dermatitis is a manifestation of Type 4 hypersensitivity.