hives hives hives, also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. hives may burn or sting. the patches of rash may appear on different body parts, with variable duration from minutes to days, and does not leave any long-lasting skin change. fewer than 5% of cases last for more than six weeks. the condition frequently recurs. hivesother namesurticariahives on the armspecialtydermatology, clinical immunology, allergologysymptomsred, raised, itchy bumpsdurationa few dayscausesfollowing an infection, result of an allergic reactionrisk factorshay fever, asthmadiagnostic methodbased on symptoms, patch testingtreatmentantihistamines, corticosteroids, leukotriene inhibitorsfrequency~20% hives frequently occur following an infection or as a result of an allergic reaction such as to medication, insect bites, or food. psychological stress, cold temperature, or vibration may also be a trigger. in half of cases the cause remains unknown. risk factors include having conditions such as hay fever or asthma. diagnosis is typically based on the appearance. patch testing may be useful to determine the allergy. prevention is by avoiding whatever it is that causes the condition. treatment is typically with antihistamines such as diphenhydramine and cetirizine. in severe cases, corticosteroids or leukotriene inhibitors may also be used. keeping the environmental temperature cool is also useful. for cases that last more than six weeks immunosuppressants such as ciclosporin may be used. about 20% of people are affected. cases of short duration occur equally in males and females while cases of long duration are more common in females. cases of short duration are more common among children while cases of long duration are more common among those who are middle aged. hives have been described at least since the time of hippocrates. the term urticaria is from the latin urtica meaning "nettle". signs and symptoms hives on the left chest wall. notice that they are slightly raised.hives drawing of hives hives, or urticaria, is a form of skin rash with red, raised, itchy bumps. they may also burn or sting. welts (raised areas surrounded by a red base) from hives can appear anywhere on the surface of the skin. 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. welts may be pinpoint in size or several inches in diameter. often the patches of rash move around. about 20% of people are affected. cases of short duration occur equally in males and females, lasting a few days and without leaving any long-lasting skin changes. cases of long duration are more common in females. cases of short duration are more common among children while cases of long duration are more common among those who are middle aged. fewer than 5% of cases last for more than six weeks. the condition frequently recurs. in half of cases of hives, the cause remains unknown. 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. cause hives can also be classified by the purported causative agent. many different substances in the environment may cause hives, including medications, food and physical agents. in perhaps more than 50% of people with chronic hives of unknown cause, it is due to an autoimmune reaction. risk factors include having conditions such as hay fever or asthma. medications drugs that have caused allergic reactions evidenced as hives include codeine, sulphate of morphia, dextroamphetamine, aspirin, ibuprofen, penicillin, clotrimazole, trichazole, sulfonamides, anticonvulsants, cefaclor, piracetam, vaccines, and antidiabetic drugs. the antidiabetic sulphonylurea glimepiride, in particular, has been documented to induce allergic reactions manifesting as hives. food the most common food allergies in adults are shellfish and nuts. the most common food allergies in children are shellfish, nuts, eggs, wheat, and soy. one study showed balsam of peru, which is in many processed foods, to be the most common cause of immediate contact urticaria. another food allergy that can cause hives is alpha-gal allergy, which may cause sensitivity to milk and red meat. a less common cause is exposure to certain bacteria, such as streptococcus species or possibly helicobacter pylori. infection or environmental agent hives including chronic spontaneous hives can be a complication and symptom of a parasitic infection, such as blastocystosis and strongyloidiasis among others. the rash that develops from poison ivy, poison oak, and poison sumac contact is commonly mistaken for urticaria. this rash is caused by contact with urushiol and results in a form of contact dermatitis called urushiol-induced contact dermatitis. urushiol is spread by contact but can be washed off with a strong grease- or oil-dissolving detergent and cool water and rubbing ointments. dermatographic urticaria main article: dermatographic urticaria dermatographic urticaria (also known as dermatographism or "skin writing") is marked by the appearance of weals or welts on the skin as a result of scratching or firm stroking of the skin. seen in 4–5% of the population, it is one of the most common types of urticaria, in which the skin becomes raised and inflamed when stroked, scratched, rubbed, and sometimes even slapped. the skin reaction usually becomes evident soon after the scratching and disappears within 30 minutes. dermatographism is the most common form of a subset of chronic hives, acknowledged as "physical hives". it stands in contrast to the linear reddening that does not itch seen in healthy people who are scratched. in most cases, the cause is unknown, although it may be preceded by a viral infection, antibiotic therapy, or emotional upset. dermatographism is diagnosed by applying pressure by stroking or scratching the skin. the hives should develop within a few minutes. unless the skin is highly sensitive and reacts continually, treatment is not needed. taking antihistamines can reduce the response in cases that are annoying to the person. pressure or delayed pressure this type of hives can occur right away, precisely after a pressure stimulus or as a deferred response to sustained pressure being enforced to the skin. in the deferred form, the hives only appear after about six hours from the initial application of pressure to the skin. under normal circumstances, these hives are not the same as those witnessed with most urticariae. instead, the protrusion in the affected areas is typically more spread out. the hives may last from eight hours to three days. the source of the pressure on the skin can happen from tight fitted clothing, belts, clothing with tough straps, walking, leaning against an object, standing, sitting on a hard surface, etc. 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 form of the skin disease is, however, rare. cholinergic or stress main article: cholinergic urticaria cholinergic urticaria (cu) is one of the physical urticaria which is provoked during sweating events such as exercise, bathing, staying in a heated environment, or emotional stress. the hives produced are typically smaller than classic hives and are generally shorter-lasting. multiple subtypes have been elucidated, each of which require distinct treatment. cold-induced further information: cold urticaria the cold type of urticaria is caused by exposure of the skin to extreme cold, damp and windy conditions; it occurs in two forms. the rare form is hereditary and becomes evident as hives all over the body 9 to 18 hours after cold exposure. the common form of cold urticaria demonstrates itself with the rapid onset of hives on the face, neck, or hands after exposure to cold. cold urticaria is common and lasts for an average of five to six years. the population most affected is young adults, between 18 and 25 years old. many people with the condition also have dermographism and cholinergic hives. severe reactions can be seen with exposure to cold water; swimming in cold water is the most common cause of a severe reaction. this can cause a massive discharge of histamine, resulting in low blood pressure, fainting, shock and even loss of life. cold urticaria is diagnosed by dabbing an ice cube against the skin of the forearm for 1 to 5 minutes. a distinct hive should develop if a person has cold urticaria. this is different from the normal redness that can be seen in people without cold urticaria. people with cold urticaria need to learn to protect themselves from a hasty drop in body temperature. regular antihistamines are not generally efficacious. one particular antihistamine, cyproheptadine (periactin), has been found to be useful. the tricyclic antidepressant doxepin has been found to be effective blocking agents of histamine. finally, a medication named ketotifen, which keeps mast cells from discharging histamine, has also been employed with widespread success. solar urticaria main article: solar urticaria this form of the disease occurs on areas of the skin exposed to the sun; the condition becomes evident within minutes of exposure. water-induced main article: aquagenic urticaria this type of urticaria is also termed rare and occurs upon contact with water. the response is not temperature-dependent and the skin appears similar to the cholinergic form of the disease. the appearance of hives is within one to 15 minutes of contact with the water and can last from 10 minutes to two hours. this kind of hives does not seem to be stimulated by histamine discharge like the other physical hives. most researchers believe this condition is actually skin sensitivity to additives in the water, such as chlorine. water urticaria is diagnosed by dabbing tap water and distilled water to the skin and observing the gradual response. aquagenic urticaria is treated with capsaicin (zostrix) administered to the chafed skin. this is the same treatment used for shingles. antihistamines are of questionable benefit in this instance since histamine is not the causative factor. exercise the condition was first distinguished in 1980. people with exercise urticaria (eu) experience hives, itchiness, shortness of breath and low blood pressure five to 30 minutes after beginning exercise. these symptoms can progress to shock and even sudden death. jogging is the most common exercise to cause eu, but it is not induced by a hot shower, fever, or with fretfulness. this differentiates eu from cholinergic urticaria. eu sometimes occurs only when someone exercises within 30 minutes of eating particular foods, such as wheat or shellfish. for these individuals, exercising alone or eating the injuring food without exercising produces no symptoms. eu can be diagnosed by having the person exercise and then observing the symptoms. this method must be used with caution and only with the appropriate resuscitative measures at hand. eu can be differentiated from cholinergic urticaria by the hot water immersion test. in this test, the person is immersed in water at 43 °c (109.4 °f). someone with eu will not develop hives, while a person with cholinergic urticaria will develop the characteristic small hives, especially on the neck and chest. the immediate symptoms of this type are treated with antihistamines, epinephrine and airway support. taking antihistamines prior to exercise may be effective. ketotifen is acknowledged to stabilise mast cells and prevent histamine release, and has been effective in treating this hives disorder. avoiding exercise or foods that cause the mentioned symptoms is very important. in particular circumstances, tolerance can be brought on by regular exercise, but this must be under medical supervision. pathophysiology