Hives are rashes on skin that are known as urticaria in medical terminology. If  it lasts for more than six weeks, it is called chronic urticaria. Hives are caused when the immune system of the body releases histamine to fight the allergens. The causes or triggers of hives are unknown most of the time but some of the common causes are; pet dander (shed skin cells), allergy from certain drugs and food.

Flower pollen and insect bites also sometimes cause hives. Overexposure to water, sun or extreme cold or heat could also cause hives. Besides these there are some other factors that can cause hives like anxiety and stress, parasitic worms, sweating and tight clothes.