Causes and Risk Factorsof Urticaria (Hives)

An allergy is not the only possible cause

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Urticaria, or hives, is a common type of rash characterized by the formation of raised, red, itchy bumps on the skin. The cause and severity of hives can vary from one person to the next. While urticaria is commonly associated with an allergy to food, medications, and other irritants, it can also have non-allergic causes such as stress, infection, autoimmune disease, and even food poisoning. Other cases are idiopathic, meaning that the cause is unknown.

Urticaria can strike anyone irrespective of age, gender, and race. It is estimated that between 15 percent and 23 percent of the adults will experience at least one bout of urticaria in their lifetime. 

acute urticaria (hives) causes
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Allergic

Allergy is the primary cause of urticaria. It is caused when the immune system responds abnormally to an otherwise harmless substance and floods the body with an inflammatory chemical known as histamine.

While the release of histamine can often trigger allergic rhinitis and other respiratory or gastric symptoms, there are others times when it will cause capillaries to swell excessively and release interstitial fluid into surrounding tissues. When this happens, the localized swelling of the dermis will lead to a well-defined rash we recognize as a hive.

There are two allergies frequently associated with urticaria:

  • Food allergies, most typically shellfish, nuts, eggs, wheat, fresh berries, chocolate, and soy
  • Drug allergies, including those triggered by certain antibiotics (like cefaclor), anticonvulsants, antifungals (like clotrimazole), aspirin, codeine, dextroamphetamine (used to treat ADHD), ibuprofen, morphine, sulfonamides, vaccines, and allergy shots

Less commonly, hives may be caused by such common allergens as pollen, pet dander, insect bites, latex, or nickel. Even less commonly, scombroid food poisoning may be the cause. This occurs when an individual consumes fish that has begun to spoil. The high concentration of histamine in the decaying flesh triggers a food "pseudoallergy" with symptoms such as diarrhea, cramps, dizziness, and widespread hives.

Most of these allergy-induced hives will resolve on their own when the allergy trigger (allergen) is removed.

Physical

Physical urticaria is a subset of hives in which the skin rash is provoked by specific environmental or physical stimuli such as cold, heat, pressure, vibration, friction, and sunlight.

While the cause of physical urticaria is unknown, it is believed to be an autoimmune response in which the body sends out defensive proteins, called autoantibodies, to attack otherwise normal tissues.

While this can trigger the same inflammatory response seen with allergic hives, the appearance of the hives is often quite different. In some cases, they will only develop in areas of skin exposed to the environmental stimuli. In others, a widespread eruption can lead to a rapid drop in blood pressure and symptoms such as headaches, flushing, blurry vision, and fainting.

Because physical urticaria is believed to be related to autoimmunity (rather than induced by an external trigger), the condition is most often chronic and can last anywhere from one to several years.

Among some the familiar (and less familiar) types of physical urticaria:

  • Aquagenic urticaria is a rare form of hives caused by contact with water.
  • Cold urticaria is an uncommon form caused by exposure to cold.
  • Cholinergic urticaria, also known as heat rash, is caused by excessive sweating and elevated skin temperatures.
  • Dermographism urticaria is caused by friction or the firm stroking of skin.
  • Pressure urticaria is caused when excessive pressure is exerted on the skin (such as when you carry a heavy bag on your shoulder).
  • Solar urticaria is caused by exposure to ultraviolet (UV) light.
  • Vibratory urticaria is caused by any form of vibration (including mowing the lawn or clapping).

Stress

In addition to physical stimuli, stress is commonly associated with the development or worsening of chronic hives. Again, the exact cause is unknown, but it is believed that the release of stress hormones such as cortisol may have a knock-on effect in which the underlying cause of hive is activated.

As such, stress may not directly "cause" hives but rather switch on or amplify the autoimmune response. One such example is cholinergic urticaria in which stress-related perspiration may instigate the development of heat rash.

Exercise

Exercise-induced urticaria is a distinctive form that is unrelated to cholinergic urticaria. It generally occurs when someone exercises within 30 minutes of eating a trigger food, such as wheat or shellfish. Exercise on its own will not cause hives.

As with stress-induced urticaria, the release of cortisol and hormones during exercise appears to intensify an otherwise low-level food allergy, increasing the concentration of histamine as well as the inflammatory response. In some cases, this can lead to a potentially life-threatening exercise-induced anaphylaxis.

Infections and Diseases

There are certain infections and diseases for which urticaria is common.

This is especially true for young children in whom 80 percent of hives are caused by a viral infection. The activation of the immune response may be triggered by something as simple as a cold. The hives tend to develop within a week of infection and usually resolve in a week or two without treatment.

Other illnesses are commonly associated with hives, many of which are autoimmune and others of which are related to an infection or malignancy. They include:

Hives caused by these types of diseases tend to be chronic or persist for as long as the underlying infection is left untreated.

Acute hives, meanwhile, can sometimes occur with shorter-acting viral, bacterial, or fungal infections such as coxsackievirus, strep throat, and even athlete’s foot.

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