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Hives: Why is this happening?

One of the most frequent questions I hear about hives is:  What’s causing them?

Up to 20% of people will experience hives (also known as urticaria) at some point in their life.  The cause of hives depends on whether they are “acute” which means they last less than 6 weeks or “chronic” which means they last longer than 6 weeks.

The causes of acute hives is frequently an allergic reaction to an environmental trigger, food, medication or insect sting.  Children with viral infections commonly experience hives.  Sometimes, however, the cause of acute hives may be elusive.

For chronic hives, the 3 main causes are idiopathic (we don’t know!), autoimmune (the body makes an antibody against itself) and physical (triggers like cold temperatures, rubbing or scratching the skin, pressure, vibration, heat, etc).  These physical triggers cause hives to last 30 minutes to 2 hours but they can recur with recurrent exposure to the trigger.   There are several other unusual types of hives where a single hive lesion can persist over 24 hours.  An example is vasculitis meaning “inflammation of blood vessels” and these can potentially be serious.  The assistance of a dermatologist to take a small skin biopsy may help identify if this is the problem.

While in general hives are not dangerous, they can be extremely itchy, which can interfere with daily activities and sleep.  Hives are not contagious. Hives can occur in all shapes and sizes (usually round to oval) and appear quite conspicuous on any part of the body.  They seem to worsen at night and with stress, but studies on this are difficult to perform.
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