Hives are one of the most common allergic skin reactions, but those itchy red welts can be brought on by more than just pet dander and pollen. In this video, Dr. Heather Viola breaks down what causes hives, which occur when the body perceives a threat and releases histamine throughout your system in response. Various allergies can cause the body to develop hives, from what you eat to different temperatures, so it’s important to determine the root cause and work with your doctor to develop an antihistamine regimen that works for you.