What is the typical delay for an Allergic Contact Dermatitis (ACD) reaction after exposure?
Answer
Usually 48 to 72 hours after contact
Allergic Contact Dermatitis (ACD) is classified as a delayed hypersensitivity reaction, contrasting sharply with the often immediate effects of irritants. This delay is characteristic of an immune system response, primarily mediated by T-cells, which require time to mobilize following re-exposure to a previously encountered allergen. The immune system needs time to recognize the substance and initiate the full inflammatory cascade. Therefore, reactions manifesting two to three days post-contact are a strong indicator that the underlying cause is ACD rather than ICD, where damage can be instantaneous or develop rapidly over hours or days.
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