Hives on the back from exposure to<unk>  air on an individual with<unk>  allergy. The hives were induced by riding a stationary bike shirtless for an hour next to a door cracked open on a cool day. The temperature of the air flowing in was around . The lighter band at chest height was covered by a heart rate monitor strap. When the body is exposed to the<unk>  in individuals afflicted by the condition, hives appear and the skin in the affected area typically becomes itchy. Hives result from dilation of capillaries which allow fluid to flow out into the surrounding tissue which is the epidermis. They resolve when the body absorbs this fluid. The border of a hive is described as polycyclic, or made up of many circles, and changes as fluid leaks out and then is absorbed. Pressing on a hive causes the skin to blanch distinguishing it from a bruise or papule. Hives can last for a few minutes or a few days, and vary from person to person. Also, a burning sensation occurs. A serious reaction is most likely to occur for patients where the hives occur with less than 3 minutes of exposure (during a<unk>  test).
Cold urticaria
Heat urticaria
Solar urticaria
Pressure urticaria
Aquagenic urticaria
Physical urticaria
Cholinergic urticaria
Delayed pressure urticaria