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<unk> . 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<unk>  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<unk> . 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<unk>  Dermatographic<unk>  (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<unk> , 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. Dermographism is diagnosed by taking a tongue blade and drawing it over the skin of the arm or back. 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<unk> e. 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 Cholinergic<unk>  (CU) is one of the physical<unk>  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 The cold type of<unk>  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<unk>  demonstrates itself with the rapid onset of hives on the face, neck, or hands after exposure to cold. Cold<unk>  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 suffer from 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<unk>  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 suffers cold<unk> . This is different from the normal redness that can be seen in people without cold<unk> . People with cold<unk>  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<unk>  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 This type of<unk>  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<unk>  is diagnosed by dabbing tap water and distilled water to the skin and observing the gradual response.<unk><unk>  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<unk>  (EU) experience hives, itchiness, shortness of breath and low blood pressure five to 30 minutes after beginning exercise. These<unk> s 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<unk> . 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<unk> s. EU can be diagnosed by having the person exercise and then observing the<unk> s. This method must be used with caution and only with the appropriate resuscitative measures at hand. EU can be differentiated from cholinergic<unk>  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<unk>  will develop the characteristic small hives, especially on the neck and chest. The immediate<unk> s 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<unk> s is very important. In particular circumstances, tolerance can be brought on by regular exercise, but this must be under medical supervision.
symptom of Aquagenic urticaria
symptom of Rosacea
symptom of Stevens–Johnson syndrome
symptom of Epidermolysis bullosa
symptom of Buruli ulcer
medical cause of Dermatitis
symptom of Hereditary angioedema
symptom of Psoriasis