Micrograph of<unk> . Dermal edema solid arrows in (A,B) and a sparse superficial predominantly perivascular and interstitial infiltrate of lymphocytes and eosinophils without signs of vasculitis (dashed arrow). Diagnosis is typically based on the appearance. The cause of chronic hives can rarely be determined. Patch testing may be useful to determine the allergy. In some cases regular extensive allergy testing over a long period of time is requested in hopes of getting new insight. No evidence shows regular allergy testing results in identification of a problem or relief for people with chronic hives. Regular allergy testing for people with chronic hives is not recommended. Acute versus chronic *<unk>  is defined as the presence of evanescent wheals which completely resolve within six weeks. Acute<unk>  becomes evident a few minutes after the person has been exposed to an allergen. The outbreak may last several weeks, but usually the hives are gone in six weeks. Typically, the hives are a reaction to food, but in about half the cases, the trigger is unknown. Common foods may be the cause, as well as bee or wasp stings, or skin contact with certain fragrances. Acute viral infection is another common cause of acute<unk>  (viral exanthem). Less common causes of hives include friction, pressure, temperature extremes, exercise, and sunlight. *<unk>  (ordinary<unk>  is defined as the presence of evanescent wheals which persist for greater than six weeks. Some of the more severe chronic cases have lasted more than 20 years. A survey indicated chronic<unk>  lasted a year or more in more than 50% of sufferers and 20 years or more in 20% of them. Acute and chronic hives are visually indistinguishable. Related conditions Angioedema Angioedema is similar to hives, but in angioedema, the swelling occurs in a lower layer of the dermis than in hives, as well as in the subcutis. This swelling can occur around the mouth, eyes, in the throat, in the abdomen, or in other locations. Hives and angioedema sometimes occur together in response to an allergen, and is a concern in severe cases, as angioedema of the throat can be fatal. Vibratory angioedema This very rare form of angioedema develops in response to contact with vibration. In vibratory angioedema, symptoms develop within two to five minutes after contact with a vibrating object and abate after about an hour. People with this disorder do not suffer from dermographism or pressure<unk> . Vibratory angioedema is diagnosed by holding a vibrating device such as a laboratory vortex machine against the forearm for four minutes. Speedy swelling of the whole forearm extending into the upper arm is also noted later. The principal treatment is avoidance of vibratory stimulants. Antihistamines have also been proven helpful.
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