If you have ever had classic urticaria, commonly known as hives, you would have experienced a transient skin disorder in which lesions are elevated with a well-circumscribed margin of redness and swelling. These skin lesions are called wheals. Wheals vary in shapes from round to oval, and are often itchy. The lesions and itchiness of hives are caused by an immunological response of the body, primarily due to the action of histamine release. Hives are generally caused by a lot of allergic conditions or diseases. Acute hives persists for less than six weeks, while chronic hives persists for at least six weeks. Hives is not a disease by itself, but it could signify underlying medical conditions or allergies.

Allergies

Foods, drugs, insect bites and contact with some substances can cause hives due to an allergic reaction. In food allergies, the body reacts to food protein. The immune system may recognize this food protein as a dangerous foreign substance. This recognition will cause a histamine release that leads to the allergic reaction symptoms. In children, food allergy is one of the major considerations in acute urticaria or hives.

The same thing happens in the immune system when a person has an allergic reaction to drugs, insect bites and substances applied on the skin. Any drug can cause an allergic reaction, but the most common drug cause of hives is antibiotic intake. Insect bites could cause venom to be injected into the body, stimulating an allergic reaction. You might have heard of people who died of bee or wasp sting. The main reason for this is a severe allergic reaction called anaphylaxis. A person could also have an allergic reaction to substances that come in contact with their skin. Examples of these substances are nickel, which is present in earrings, necklaces and belt buckles, and the sap of poison ivy.

Certain Medical Conditions

Some infections, along with hormonal, endocrine and autoimmune diseases can cause hives. These include hepatitis B and C infections, excessive or deficient thyroid hormone production, systemic lupus erythematosus and rheumatoid arthritis. If you have any of these conditions, you are at increased risk of experiencing hives.

Physical Causes of Hives

Physical causes of hives include pressure, sunlight, cold weather and cholinergic urticaria. In dermographism, hives can be seen on areas subjected to light pressure or scratching of skin. Exposure to sunlight can produce hives within minutes, and is commonly associated with a systemic disease called erythropoietic protoporphyria. Exposed areas of your body to cold are usually affected with hives if you have an abnormality in your circulating body proteins. Cholinergic urticaria is triggered by heat, emotional stress or exercise. Other physical causes of hives are vibration and water.

Unknown Cause

Hives due to an unknown cause is called idiopathic urticaria. The cause is unknown because it cannot be specifically identified by the history of symptoms, physical examination findings and laboratory workups. Idiopathic urticaria commonly presents in chronic form. Chronic idiopathic urticaria is present in 80 to 90 percent of individuals, and these may have associated physical causes (such as pressure and cold) of urticaria.