Urticaria (hives)

General: Many allergens, including foods and medications, can trigger allergic reactions that cause urticaria (hives). The more exposure a person has to common allergens, the greater the chance that he/she will become allergic. That is why occupational exposure to allergens is a common cause of hives. For instance, bakers are more likely to develop allergies to yeast, flour, or grains, and landscapers are more likely to develop allergies to pollen. Medical conditions including autoimmune disorders, infections, and physical factors may cause hives.

Antibody production: Urticaria may occur in response to the body's production of antibodies. Antibodies are proteins produced by the immune system to fight specific bacteria, viruses or other foreign substances that enter the body. This might occur as the result of blood transfusions, immune system disorders (like lupus or cancer), certain thyroid disorders, or infections (as serious as hepatitis or as mild as a cold).

Animal dander: Animals secrete oily fluids from their skin, which contain allergens called dander. These fluids collect on fur, feathers, and other surfaces inside the home causing allergic reactions in sensitive people. Proteins in the animal's saliva also cause allergic reactions. These allergens are so small that they may become airborne for extended periods of time

Autoimmune disorders: Autoimmune disorders, such as systemic lupus erythematosus (SLE), account for up to 50% of all cases of chronic urticaria, according to researchers. Autoimmune disorders are conditions caused by an immune response against the body's own tissues. The immune system mistakes its own cells for foreign invaders like bacteria or viruses.

Foods: Food allergens are those parts of foods, usually proteins, which lead to allergic reactions that may cause hives. Most allergens can still cause allergic reactions even after they are cooked or have been digested. However, some allergens (usually from fruit and vegetables) only cause allergic reaction if eaten raw. These reactions are usually limited to the mouth and throat. According to the American Academy of Allergy, Asthma & Immunology (AAAAI), six foods, including milk, peanuts, soy, eggs, wheat, and tree nuts (like pecans and walnuts), cause 90% of food allergies in children. Children usually outgrow allergies to milk, eggs and soy, but peanut, tree nut, fish and shellfish allergies continue throughout adulthood.

Immune disorders: Other disorders of the immune system, including cryoglobulinemia, cryofibrinogenemia, syphilis, mastocytosis, Muckle-Wells syndrome, and familial cold auto-inflammatory syndrome, may cause hives.

Infections: Many infections may cause urticaria. Viral upper-respiratory tract infections (colds or URIs) are a common cause of hives in children. Other viruses, such as hepatitis (liver inflammation) and many bacterial and fungal infections, may cause urticaria as well.

Insect venom: The honeybee, yellow jacket, paper wasp, white-faced hornet (bald-faced hornet), and fire ant are among the most common insects that trigger insect sting or bite allergies that often result in hives. Since the stinger is a modified egg-laying apparatus, only females can sting.

Latex: Latex, a substance found in products like rubber gloves or condoms, can also trigger allergic reactions that cause hives. A component of the latex substance itself is an allergen. Latex reactions may cause a potentially life-threatening allergic reaction called anaphylaxis.

Medications: Almost any medication may cause hives. Antibiotics (such as penicillin), aspirin, ibuprofen (Advil® or Motrin®), glimepiride (Amaryl®), and blood pressure medications frequently cause allergic reactions. There can be cross sensitivity to a different medication in the same drug class.

Pollen: Each spring, summer, and fall, plants release tiny particles called pollen into the air in order to reproduce. Pollen from plants, such as ragweed, can trigger allergy symptoms, including hives.

Physical factors: Environmental factors, such as heat, cold, sunlight, water, pressure on the skin, emotional stress, and exercise, may also cause hives in some people.

Urticaria (hives) can be either acute or chronic. Acute hives can last less than a day or up to six weeks. Chronic hives may last longer than six weeks. In some cases, they can occur for months to years at a time. Hives cause red, itchy welts to form on the skin often accompanied by sensations of warmth. When urticaria forms in response to the cold or the water, symptoms may include wheezing, flushing, generalized hives, and fainting.

In rare instances, hyperpigmentation (darkening of the skin) or hypopigmentation (light spots of the skin) may also occur.

Drug-induced urticaria may cause severe heart and lung failure.

Urticaria can be diagnosed after a physical examination and medical history. Healthcare providers will then conduct tests to determine the cause. Allergy testing with either skin tests or allergen-specific immunoglobulin E tests may be performed to detect specific allergies. A fluorescent antinuclear antibody test (FANA) may be performed to determine whether the condition is caused by an autoimmune disorder.

Skin test: A skin test is used to determine whether a patient is allergic to certain substances, such as mold, dust mites, or animal dander. During the test, the skin is exposed to different allergy-causing substances (allergens) and then observed for an allergic reaction. Some tests, like the percutaneous (puncture, prick, or scratch) test, detect immediate allergic reactions that develop within minutes of exposure to an allergen. Other tests, like the epicutaneous (patch) test, detect delayed allergic reactions that develop over the course of several days. If an allergen triggers an allergic reaction to a test, the patient will develop reddening, swelling, or a raised, itchy red wheal (bump) that looks similar to a mosquito bite. The healthcare provider will measure the size of the wheal and record the results. The larger the wheal, the more severe the allergy.

Allergen-specific immunoglobulin E (IgE) test: An allergen-specific immunoglobulin E (IgE) test, commonly referred to as radioallergosorbent test (RAST®), may also be used to determine whether the patient is allergic to specific substances. However, this test is less accurate than a skin test. It is usually performed in patients who have coexisting severe skin diseases (such as eczema or psoriasis) that make it difficult to interpret a skin test.

The in vitro test is conducted outside of the body in a laboratory setting. During the procedure, a sample of blood is taken from the patient. The blood is then sent to a laboratory that performs specific IgE blood tests. The allergen is bound to an allergosorbent (paper disc). Then the patient's blood is added. If the blood contains antibodies (immunoglobulins that detect and bind to antigens) to the mold antigens, the blood will bind to the allergen on the disc. A radiolabelled ANTI-IgE antibody is then added to the disc to measure the level of immunoglobulin E present in the blood. The higher the radioactivity, the higher the level of IgE in the blood and the more severe the allergy.

A qualified healthcare provider will interpret the results of the test. In general, the sensitivity of these tests range from 50-90%, with the average being about 70-75%. The patient will receive test results in about seven to 14 days.

Fluorescent antinuclear antibody test (FANA): The fluorescent antinuclear antibody test (FANA) is used to determine whether autoimmune disorders, such as systemic lupus erythematosus (SLE), scleroderma, Sjögren's syndrome, Raynaud's disease, juvenile chronic arthritis, rheumatoid arthritis (RA), or antiphospholipid antibody syndrome, are causing hives. The FANA test is a blood test used to detect abnormal antibodies, called autoantibodies. The autoantibodies bind to components of and individual's own cells and cause the immune system to attack the body.

To measure results, human tissue culture cells (HEp-2 cell line) are grown in culture and applied to a microscope slide. The slides are then treated with methyl alcohol to make the cells permeable before they are combined with the patient's blood. The cells are incubated with fluorescent antibodies that detect the binding of human antibodies to the cells. The slide is then observed with a fluorescence microscope. The intensity of the staining and the binding pattern are scored at various dilutions.

A positive test result may suggest an autoimmune disease, but further testing is needed to make a specific diagnosis. FANA test results can be positive in people who do not have autoimmune diseases. While a false positive result is uncommon, the frequency increases as people age. A false negative result is also possible, but it is uncommon.