This is true. In delayed hypersensitivity reactions like poi-son i-ii-i-vy there is usually an interval of a few days between the time of exposure and the development of the characteristic rash. That is, it takes awhile for the immune reaction to develop its full intensity. In contrast, in immediate hypersensitivity the reaction develops, well, immediately after exposure. These reactions are characterized by hives, swelling, and sometimes difficulty breathing. Bee sting allergy is a typical example familiar to most birders.

Bruce MacPherson
South Burlington

In a message dated 01/22/08 16:20:39 Eastern Standard Time, [log in to unmask] writes:
The phenomenon is called delayed hypersensitivity, I believe, and one can develop same over time. BTDT. 

Anthony Hill 
S. Hadley, MA 

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