[2] The patches of rash may appear on different body parts,[2] with variable duration from minutes to days, and do not leave any long-lasting skin change.

[2][4] Hives frequently occur following an infection or as a result of an allergic reaction such as to medication, insect bites, or food.

Whether the trigger is allergic or not, a complex release of inflammatory mediators, including histamine from cutaneous mast cells, results in fluid leakage from superficial blood vessels.

Hives may be pinpoint in size or several inches in diameter, they can be individual or confluent, coalescing into larger forms.

[2] Cases of short duration occur equally in males and females, lasting a few days and without leaving any long-lasting skin changes.

[2] Angioedema is a related condition (also from allergic and nonallergic causes), though fluid leakage is from much deeper blood vessels in the subcutaneous or submucosal layers.

Individual hives that are painful, last more than 24 hours, or leave a bruise as they heal are more likely to be a more serious condition called urticarial vasculitis.

Hives caused by stroking the skin (often linear in appearance) are due to a benign condition called dermatographic urticaria.

Urushiol is spread by contact but can be washed off with a strong grease- or oil-dissolving detergent and cool water and rubbing ointments.

Seen in 4–5% of the population, it is one of the most common types of urticaria,[12] in which the skin becomes raised and inflamed when stroked, scratched, rubbed, and sometimes even slapped.

The areas of the body most commonly affected are the hands, feet, trunk, abdomen, buttocks, legs and face.

Although this appears to be very similar to dermatographism, the cardinal difference is that the swelled skin areas do not become visible quickly and tend to last much longer.

This can cause a massive discharge of histamine, resulting in low blood pressure, fainting, shock and even loss of life.

Finally, a medication named ketotifen, which keeps mast cells from discharging histamine, has also been employed with widespread success.

[citation needed] This form of the disease occurs on areas of the skin exposed to the sun; the condition becomes evident within minutes of exposure.

Ketotifen is acknowledged to stabilise mast cells and prevent histamine release, and has been effective in treating this hives disorder.

[citation needed] Hives are caused by the release of histamine and other mediators of inflammation (cytokines) from cells in the skin.

Basophils and other inflammatory cells are also seen to release histamine and other mediators, and are thought to play an important role, especially in chronic urticarial diseases.

Roughly 50% of people with chronic urticaria spontaneously develop autoantibodies directed at the receptor FcεRI located on skin mast cells.

Also, a diverse group of signaling substances called neuropeptides, have been found to be involved in emotionally induced hives.

Ingestion of free histamine released by bacterial decay in fish flesh may result in a rapid-onset, allergic-type symptom complex which includes hives.

[21] A large body of evidence demonstrates an association between this condition and both poor emotional well-being[22] and reduced health-related quality of life.

[29][30] No evidence shows regular allergy testing results in identification of a problem or relief for people with chronic hives.

Vibratory angioedema is diagnosed by holding a vibrating device such as a laboratory vortex machine against the forearm for four minutes.

[citation needed] The mainstay of therapy for both acute and chronic hives is education, avoiding triggers and using antihistamines.

[citation needed] First generation antihistamines, such as diphenhydramine or hydroxyzine, are not recommended as a first line therapy as they block both brain and peripheral H1 receptors, causing sedation.

Significant improvement in pruritus and quality of life was observed in a phase III, multicenter, randomized control trial.

[49][50] Immunosuppressants are generally reserved as the last line of therapy for severe cases due to their potential for serious adverse effects.

[4] Chronic urticaria is often accompanied by an intense pruritus, and other symptoms associated with a reduced quality of life and a high burden of co-morbid psychiatric conditions such as anxiety and depression.

[57] The history of urticaria dates back to 1000–2000 BC with its reference as a wind-type concealed rash in the book The Yellow Emperor's Inner Classic from Huangdi Neijing.