Hives, known in the medical literature as urticaria, are a localized itchy outbreak of the skin. in this essentially allergic reaction, the skin breaks out in bumps surrounded by elongated flares. These hives are referred to as wheals or welts. the welts tend to be pink except that they turn white when touched. Welts may coalesce into plaques covering substantial areas of skin.
Hives are intensely itchy. they may involve any area of the body from the scalp to the soles of the feet, and appear in crops of 24- to 72-hour duration. the most common sites for outbreaks are the hands, feet, and face. Angioedema, a swelling below the skin caused by the same allergic mechanism, usually occurs around the eyes and in the lips. While the itchy bumps usually go away without treatment, angioedema in the upper respiratory tract may be life threatening and requires immediate medical attention.
A survey of college students indicates about one in five people has hives at some point in life. they may occur at any age, but young adults in their twenties are the most frequently affected. the precise causes of the condition vary person to person.
Aspirin sensitivity is observed in up to 67 percent of persons who have recurrent outbreaks of hives. Aspirin alters the metabolism of free fatty acids so that it favors the production of leukotrienes. These are hormonal messengers that make the walls of blood vessels more permeable to histamine. Aspirin also makes the lining of the intestines more permeable to allergens, increasing the risk of reaction to common food allergens such as cheese, chocolate, eggs, milk, pineapple, shellfish, and strawberries. at least one study found taking a single adult aspirin daily for three weeks desensitizes the immune system to aspirin and also to foods, but the benefits vanish if aspirin is discontinued.
Two factors increase the risk of outbreaks of hives after eating allergenic foods. One is incomplete digestion. a study published in the 1940′s reported that of 77 patients diagnosed with chronic hives, 65 had failures to produce enough stomach acid to break down the proteins that cause allergies. Treatment with hydrochloric acid and a vitamin B complex relieved symptoms in most of the patients in the study. Failure to secrete sufficient gastric acid is especially common in persons over the age of 60. it may be a major contributing factor in repeated outbreaks of hives after consuming allergenic foods in older persons.
Another contributing factor to recurrent food allergies is the permeability of the intestinal wall. this is the reason reactions to food are more severe when they are consumed after taking aspirin. Aspirin irritates the lining, increasing its permeability and easing transport of allergens into the bloodstream. Alcohol, NSAIDs, and many food additives have a similar effect. Consuming any substance that irritates the lining of the digestive tract increases the severity of the food allergy that causes hives.
Food colorings, especially yellow dye #5 (tartrazine), can provoke hives in about 0.1 percent of the population. Tartrazine is added to almost every food and even antihistamines, antibiotics, sedatives, and steroids. this yellow dye modifies fatty acid metabolism in the same manner as aspirin and increases the susceptibility of the skin to allergic inflammation.
Food flavorings are a major factor in many cases of hives in children. a wide range of salicyclic acid esters flavors cake mixes, chewing gum, puddings, and soft drinks. These chemical relatives of aspirin also occur naturally in curry powder, dill, licorice, oregano, paprika, peppermint, prunes, raisins, and turmeric. the average child consumes as much 200 mg of salicylate per day. this dosage approaches the amount of salicylate in children’s aspirin. Other flavorings, including aspartame, cinnamon, menthol, and vanilla may produce urticaria in some individuals.
The food preservatives BHA (butylated hydroxyanisol) and BHT (butylated hydroxytoluene) provoke reactions in about 15 percent of individuals who have chronic hives. As many as 44 percent of persons with chronic urticaria are allergic to benzoates, which occur in relatively high concentrations in fish and shrimp. Sulfites, which are sprayed on fruits, vegetables, and shrimp to keep them fresh in countries outside the United States, aggravate a wide range of allergic conditions, including asthma as well as hives. Sulfites occur naturally in beer and wine.
About 1 in 10 people is allergic to penicillin, and about 1 in 4 of those allergic to penicillin will develop urticaria, angioedema, or anaphylaxis after taking it. Penicillin is a common additive to livestock feeds. both skin outbreaks and anaphylactic reactions have been traced to penicillin in frozen dinners, milk, and soft drinks. Among patients with chronic hives and an allergy to penicillin, about half will improve on a dairy-free diet.