Researchers have identified many – but not all – of the factors that can cause hives. These include food and other substances you take, such as medications. Some people develop hives just by touching certain items. Some illnesses also cause hives. Here are a few of the most common causes:
- Some food (especially peanuts, eggs, nuts and shellfish)
- Medications, such as antibiotics (especially penicillin and sulfa), aspirin and ibuprofen
- Insect stings or bites
- Physical stimuli such as pressure, cold, heat, exercise or sun exposure
- Blood transfusions
- Bacterial infections, including urinary tract infections and strep throat
- Viral infections, including the common cold, infectious mononucleosis and hepatitis
- Pet dander
- Some plants, such as poison oak and poison ivy
Antihistamines – available either over the counter or by prescription – are a frequently recommended treatment for hives. They work by blocking the effect of histamine, a chemical in the skin that can cause allergy symptoms, including welts. Low-sedating or nonsedating antihistamines are preferred. They are effective and long-lasting (may be taken once a day) and have few side effects. Your allergist may recommend a combination of two or three antihistamines to treat your hives, along with cold compresses or anti-itch salves to ease the symptoms.
Severe episodes of urticaria may require temporary treatment with prednisone, a similar corticosteroid medication or an immune modulator, which can reduce the severity of the symptoms.
If your reaction involves swelling of your tongue or lips, or you have trouble breathing, your allergist may prescribe an epinephrine (adrenaline) auto-injector for you to keep on hand at all times. These can be early symptoms of anaphylaxis, a potentially fatal allergic reaction that impairs breathing and can send the body into shock. The only treatment for anaphylaxis is epinephrine. If you develop hives and your injector is not nearby – or if using the auto-injector doesn’t cause the symptoms to immediately improve – go to an emergency room immediately. You should also go to the emergency room after using an auto-injector.
If the cause of hives can be identified, the best treatment is to avoid the trigger or eliminate it:
- Foods: Don’t eat foods that have been identified to cause your symptoms.
- Rubbing or scratching: Avoid harsh soaps. Frequent baths may reduce itching and scratching, which can make the hives feel worse.
- Constant pressure: Avoid tight clothing. Pressure hives can be relieved by wearing loose-fitting clothes.
- Temperature: If you develop hives when exposed to cold, do not swim alone in cold water and always carry an epinephrine auto-injector. Avoid exposure to cold air and use a scarf around your nose and mouth in cold weather. If you must be out in the cold, wear warm clothing.
- Sun exposure: Wear protective clothing; apply sunblock.
- Medications: Notify your physician or pharmacist immediately if you suspect that a specific medication is causing your hives.
Some cases of hives last for more than six weeks and can last months or years. This condition is known as chronic hives.
If the cause cannot be identified, even after a detailed history and testing, the condition is called chronic idiopathic urticaria. (“Idiopathic” means “unknown.”) About half these cases are associated with some immune findings. Chronic hives may also be associated with thyroid disease, other hormonal problems or, in very rare instances, cancer. Even this condition usually dissipates over time.
In physical urticaria, the hives have a physical cause, such as exposure to heat, cold or pressure.
Common triggers include:
- Rubbing or scratching (simple dermographism). This is the most frequent cause of physical urticaria. Symptoms appear within a few minutes in the place that was rubbed or scratched and typically last less than an hour.
- Pressure or constriction. Delayed pressure urticaria can appear as red swelling six to eight hours after pressure (belts or constrictive clothing, for example) has been applied. Symptoms can also occur in parts of the body under constant pressure, such as the soles of the feet.
- Change in temperature. Cold urticaria is caused by exposure to low temperatures followed by re-warming. This can be severe and life-threatening if there is a general body cooling – for example, after a plunge into a swimming pool.
- Higher body temperature. Cholinergic urticaria is due to an increase in body temperature because of sweating, exercise, hot showers and/or anxiety.
- Sun exposure. Solar urticaria may occur within a few minutes after exposure to the sun.
Inflammation of the blood vessels, or vasculitis, can also cause hives. These hives are more painful than itchy, may leave a bruise on the skin and often last more than a day.