Cool/cold surfaces: Sitting on sidewalks which are cool, leaning on or grabbing a cold pole can result in hives forming on the area which had contact with the cool surfaces. Cold IV lines:  Sometimes IV lines are cold, which can result in a reaction. A line of hives may appear within 6 to 8 inches from the IV site in the pattern of a line going up the limb. Activities:
Cold foods and drinks: Eating or drinking cold or cool substances such as ice cream or iced tea may result in a reaction inside the mouth and throat. Swimming: Swimming can be especially dangerous, as the rapid heart rate combined with the onset of hives can lead to hypotension, shock, and drowning. Sweat: A reaction may even occur on a warm day when there is sweat on the skin, since the reaction is triggered by skin temperature, not core temperature. If there is a breeze, it will rapidly cool the skin and create hives. Restriction of blood flow: Activities which cause tense muscles and reduce blood flow can cool the body parts enough to trigger itching and hives. Drugs
The first-line therapy is symptomatic relief with second-generation H1-antihistamines.
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 (turn pale as blood flow is interrupted), distinguishing it from a bruise or papule. Hives may appear immediately or after a delay. 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 cold test). Cause
The hives are a histamine reaction in response to cold stimuli, including a drastic drop in temperature, cold air, and cold water. There are many causes for cold hives, most are idiopathic (meaning they have no known cause). Some rare conditions can cause cold hives, and it can be useful to test for these conditions if the cold hives are in any way unusual. Scientists from the USA National Institutes of Health have identified a genetic mutation in three unrelated families that causes a rare immune disorder characterized by excessive and impaired immune function: immune deficiency, autoimmunity, inflammatory skin disorders and cold-induced hives (cold urticaria). "The mutation discovered occurs in a gene for phospholipase C-gamma2 (PLCG2), an enzyme involved in the activation of immune cells.