The Allergy Kit

About Hives


Hives, also known as Urticaria or wheals, is a skin condition characterized by raised welts or itchy red bumps. The welts can range in size from between one millimeter to several centimeters in diameter. They are generally pale at the center and are surrounded by an area of redness and warmth. Hives may appear anywhere on the skin and cover either a small area or significant portions of the body. Urticaria can be itchy and can last for up to 48 hours, although it normally fades away in less than 24 hours. Although they may not last for more than 24 hours, during that period they can appear, disappear and reappear in various locations on the body. Sometimes urticaria will disappear without a trace but in other cases, it is replaced by a new rash.

Urticaria can be either acute or chronic. An episode is considered acute if it lasts for less than six weeks. It is considered chronic if the cycle lasts for more than six weeks. Although most cases of chronic urticaria resolve in less than a year, it can persist for a decade or longer and do so in approximately 10% of people who experience them. In most instances, chronic urticaria is of unknown origin. In some instances, doctors may be able to determine that a patient’s urticaria is caused by allergy but they are unable to pinpoint the responsible allergen. In other instances, the doctor may not be able to determine whether the urticaria is caused by allergy or by some other condition. Urticaria is always linked to allergies but if there is a relationship, it is usually due to food, insect stings, medication, and animal dander.


The skin contains approximately 10,000 per cubic millimeter of mast cells. These mast cells contain histamine and other mediators. If a person is exposed to an allergen that causes these mast cells to release histamine, the resulting reaction may cause the skin to break out into hives. Urticaria is caused by allergens that are either inhaled, ingested or injected as well as by those allergens that come into contact with the skin.

Hives can be caused by physical stimuli such as heat, cold and pressure; by systemic rheumatic diseases; by infectious diseases; by the use of drugs that directly cause mast cells to release mediators; and by the use of drugs. The allergens that most commonly cause urticaria are foods, drugs, and insect venom. Food allergy is one of the most frequent causes of acute urticaria. Urticaria can also be caused by food additives, preservatives, and dyes. The most common medications to cause urticaria are penicillin, sulfa antibiotics, diuretics, and certain anesthetics.

Insect stings from honeybees, yellow jackets, and fire ants are a common cause of hives. The anticoagulants that mosquitoes and fleas deposit in the skin when they bite and the saliva of the kissing bug may also cause urticaria. Inhalant allergens, physical contact with grass, animal dander, and dust mites have been known to cause urticaria. Physical stimuli can also cause urticaria, such as allergic reactions to cold, heat, exercise-induced allergy, pressure on the skin, solar induced urticaria, and reactions that are water induced.

Cold urticaria is caused by exposure to cold. The wheals, which are usually red, itchy and swollen, develop within several minutes of exposure to cold – cold air, cold water or cold food or drink. Only areas exposed to the cold are affected, although an anaphylactic reaction can occur if the area exposed to the cold is very large – if the person swims in cold water, for instance. In general, however, these wheals are harmless and short-lived, disappearing within one or two hours.

Cholinergic urticaria occurs when the body’s core temperature is heated, either by direct exposure to heat or hot water or by exercise or anxiety. Cholinergic urticaria generally involves very small, round and itchy wheals. These wheals are often brought on by a hot shower or bath and are often mistaken for an allergy to soap or shampoo.

Exercise induced anaphylaxis, in which vigorous physical exertion produces urticaria and alters respiratory and gastrointestinal symptoms (and occasionally vascular collapse), is not caused by an elevation of the core body temperature. In nearly half of the people affected by exercise-induced anaphylaxis, symptoms develop only when exercise occurs within a few hours after they have ingested a food to which they test allergic. In other people, symptoms occur when they exercise after a meal, no matter what food they’ve eaten.

Pressure urticaria occurs in people whose skin is sensitive to pressure. The most common form of this is called dermatographism. In dermatographism, wheals develop at the site of firm stroking on the skin. People with dermatographism can actually write or draw on their skin by stroking on it: The area which they have “written” becomes red, swollen and itchy. In other instances, pressure urticaria develops anywhere the skin is under pressure – under tight clothing or elastic for example.

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In addition to allergies, viral infections, intestinal parasites, and other diseases can cause urticaria, so the doctor must determine whether the urticaria is allergic or nonallergic. Patient history and a physical examination are the most useful tools in making a diagnosis. The presence of the following factors also helps to indicate that the urticaria is allergy related:

  • a reaction that seems to be caused by a substance that affects only a small percentage of people
  • exposure to the substance in the past without symptoms of a reaction developing
  • worsening symptoms with each time there is a reaction

  • When the doctor is able to identify the offending substance, a patient should avoid that particular allergen if at all possible.


    The most effective treatment for hives is avoiding the offending substance. In some cases, such as when airborne allergens or insect sting allergens cause the urticaria, allergy shots can help. Once an outbreak of urticaria is under way, topical corticosteroid creams can help the rash and oral antihistamines can relieve the itch. The doctor may prescribe oral corticosteroids for severe cases.

    It is important to note that hives are sometime the first sign of a life threatening anaphylactic reaction. If shortness of breath, wheezing, difficulty in swallowing, nausea, weakness, or confusion occur after the outbreak of urticaria, emergency medical treatment must be sought immediately.


    The best practice to prevent urticaria from occurring is to avoid the offending substances that cause a reaction. This is not always possible as some people react to the environment such as pollen or temperature. Tips to minimize the occurrence of urticaria include:

    • Avoid extreme heat
    • Wear loose clothing to avoid rubbing against the skin
    • Do not scratch the affected areas of skin

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    Hives can appear very suddenly in response to environmental factors or allergens. As situations are not always avoidable, a person who suffers from urticaria can not always prevent the onset of symptoms. There are treatments available for urticaria so getting properly diagnosed by a physician is the first step in controlling further outbreaks.

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