What are hives?

A vascular reaction: Hives are slightly elevated patches of skin caused by increased blood flow. The hives are usually caused by histamine release, which dilates blood vessels and causes the resultant edema. The hives are usually surrounded by a red halo - a flare - which comes from a reactive skin flush. The irritated nerve endings in the vicinity of the hive will send off "itching" signals.

Skin rash : That is characteristically raised, evanscent, and itchy.