Hives
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http://www.riversideonline.com/health_reference/Disease-Conditions/DS00313.cfm
This skin abnormality is called hives. Hives are caused when your body is having an allergic reaction to something. They usually itch and appear to be swollen redish colored welts on your body. Hives are usually found all over your body, there's not one specific place that hives show up because its due to an allergic reaction. Hives usually take care of themselves, they usually go away on their own if the reaction is small but in other cases when the reaction is bigger a person may need to get a shot of adrenaline, or steroids from their doctor. Ways to prevent hives are basically just know what your allergic to and don't come in contact with it, and hives may also occur as a result to emotional stress, extreme cold or sun exposure, illness or infections. The main health risk associated with hives is anaphylaxis, a whole body reaction which narrows or completely closes the airway, when this happens hives become life threatening. Hives don't affect anything other than the skin because its simply just a raised welt on the body.
Q1: Is there a difference in the appearance of the hives if it's caused by an allergic reaction as opposed to an infection such as hepititis, which is known to causes hives? (J. Murray)
A1:

Q2:Are the hives different if they are due to a stress than if they were due to an allergic reaction?(M.White)
A2:

Q3:Does every allergic reaction involve Hives?(E.Stanko)
A3: Yes, hives are a way for your body to tell you that something isn't right. An allergic reaction causes histamine to be released underneath the skin and causes the skin to swell.

Q4:How soon do the hives usually appear? (D. Antunes)
A4: Hives can appear almost immediately but could also take hours for them to become visible.

Q5:Is there treatment you can receive from a doctor after hives appear? (A.Donaldson)
A5: Yes there is. Usually hives will disappear on their own, but if the reaction is too severe they may need to go to the doctor to get an injection of adrenaline or steroids.