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How long for an allergic reaction to start after you apply substance?

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Dr. Barbara Stark Baxter
Internal Medicine - Allergy & Immunology

In brief: Skin allergies

The commonest allergic reaction due to skin contact is allergic contact dermatitis.
This usually shows up 48-72 hours after you touch the allergen, like poison ivy, but in a hypersensitive person, the time-course can be accelerated. A skin reaction to an allergen for which the body has made ige shows up nearly immediately, within minutes. We use this when we do prick skin testing.

In brief: Skin allergies

The commonest allergic reaction due to skin contact is allergic contact dermatitis.
This usually shows up 48-72 hours after you touch the allergen, like poison ivy, but in a hypersensitive person, the time-course can be accelerated. A skin reaction to an allergen for which the body has made ige shows up nearly immediately, within minutes. We use this when we do prick skin testing.
Dr. Barbara Stark Baxter
Dr. Barbara Stark Baxter
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