id reaction

Intense inflammatory diseases of the skin, such as more severe fungal infections of the feet or scalp, can produce a strange itchy, vesicular eruption, which occurs most commonly on the sides of the fingers but may be generalized over the rest of the body. This type of eruption is known as an id reaction.

The eruption usually confuses everybody for a while, but resolves as the inflammation that initiated it resolves. The id reaction is probably an allergic reaction to fungi or to some antigen created during the inflammatory process. The diagnosis of an id reaction should properly not be made unless there is an acute inflammatory process at a distant site and the id reaction disappears shortly after the acute inflammation is controlled.

It is often confused with dyshidrotic eczema eruptions, which occur on the palms and soles as well and are much, much more common. But it is one of those odd conditions we are suppposed to remember from dermatology class in med school, so we doctors are looking for it and rather proud of ourselves to remember it 8-)

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