Hives, called urticaria by doctors, is one of the most common causes of skin inflammation. Up to 20% of the population will suffer from urticaria at least once in their lives.
Large, itchy red rashes called hives rise up and disappear quickly, sometimes to be replaced by others. A few people find that the condition recurs or lasts more than 6 weeks, which is considered chronic urticaria.
Hives appear as a reaction to an external irritant that is ingested or comes in contact with the skin. In response to the irritant, the body releases chemicals such as histamine that cause itching and inflammation. Irritants can include certain foods, medications, cosmetic products, insect stings, chemicals, infections, and certain medical problems, and even exposure to extreme heat or cold.
In a minority of people with hives, a clear allergic link can be proven. They develop rashes after eating certain foods, taking certain medications, or being stung by an insect. Foods that can be associated with hives include:
- fish and shellfish
Coffee, alcohol, and tobacco are rarely identified as triggers of acute attacks of hives, but people who suffer from chronic hives often report that these substances make their symptoms worse.
Almost any medication can provoke hives. These are some of the most common culprits:
- acetylsalicylic acid* (ASA) and other anti-inflammatory medications (e.g., ibuprofen, naproxen)
- angiotensin converting enzyme inhibitors (ACE inhibitors; e.g., ramipril, lisinopril, and enalapril)
- antibiotics such as penicillins and sulfonamides
- antiepileptic medications (e.g., carbamazepine, phenytoin)
- anesthetics (e.g., lidocaine)
- codeine and other narcotic painkillers
If you get a rash from medications or food, it may not be the primary ingredient that's causing the problem. It could be a preservative or other additive. For example, if several different foods and medications seem to give you hives, you may be reacting to tartrazine, a colouring agent frequently used in pills and food.
Cosmetics, soaps, perfumes, and lotions can also cause reactions. Often, this will only occur when you switch to a new type. This may make it easier to identify the cause of your hives.
Other common irritants are nickel in jewellery and latex in gloves or condoms.
Allergic urticaria is the name given to hives caused by allergic reactions to food, insect bites, medications, or makeup. Other types are caused by physical irritation, such as sunlight, cold, or rubbing of the skin. While we don't call these types allergic, the underlying process is much the same.
Hives brought on by sunlight (solar urticaria) may not seem like an allergic condition at first sight, but the evidence suggests it is. The exact cause of solar urticaria is unclear, but it is thought that in some people, a substance in the skin turns into an allergen once sunlight hits it.
The same is true of hives caused by cold temperatures. It seems likely that the blood of people with these conditions carries abnormal immune cells. These cells attack when confronted with chemicals that are normally released in the skin by cold, sunlight, or some other external circumstance.
Dozens of infections can cause hives, including throat, stomach, and genital or urinary (genitourinary) tract infections; fungal infections; mononucleosis; and hepatitis. The common cold often causes hives in children. Hives aren't directly caused by the infectious organism, as in chickenpox or cellulitis. Rather, they're caused by "friendly fire" from the human body's own defences.
Other triggers frequently associated with hives include:
- friction – about 2% to 5% of the population are prone to developing skin rashes after gentle rubbing or scratching of the skin; this condition is called dermatographism. Repetitive scratching of the hives may worsen the condition
- swimming, which can cause fairly severe reactions, probably more due to the cold than to the water
- exercise, stress, and hot showers, which cause a form of hives called cholinergic urticaria
- pressure from belts, straps, and elastic, causing pressure urticaria
- pregnancy – hives often appear late in pregnancy
Chronic or recurring hives might mean you're being repeatedly exposed to a trigger, or it might be a sign of underlying disease. Lupus, rheumatoid arthritis, thyroid disorders, and other autoimmune disorders are diseases likely to cause hives to appear.
Symptoms and Complications
Hives are itchy, red welts on the skin. They may join together to form one big rash or may be spread out to form several smaller ones. They're often large and slightly raised. The edge of the rash is often the most inflamed part, with the centre being paler in colour. There may be pain or burning instead of itching. Symptoms often seem more severe at night.
Acute hives usually last no more than 24 hours in a given location on the body; bouts of acute hives can last up to 6 weeks. Chronic hives can last for more than 6 weeks. Most cases however, last about a week.
Occasionally the rash is more than skin deep. If histamine and other inflammatory agents are released into the layers just under the skin, the swelling is more severe and itching is likely to be replaced by pain. This condition is called angioedema.
Angioedema can cause alarming swelling in the mucous membrane of the lips, mouth, gut, genitals, or throat. The swelling usually goes down within a day, but very rarely it interferes with breathing and requires emergency treatment. If you experience hives that are associated with dizziness, difficulty breathing, throat swelling, angioedema, fever or yellowing of the eyes or skin, get immediate medical attention.
Making the Diagnosis
Your doctor will try to identify the trigger by asking when the rash appeared and what you might have done that was different from usual in the days leading up to it. Blood tests generally reveal very little about hives. In many cases (at least half), the cause remains a mystery. It usually doesn't matter, because hives are a brief, solitary event for most people.
Your doctor may ask you to keep a record of what you eat and your activities to try to pinpoint the cause.
If hives last more than 48 hours and the diagnosis is unclear, a skin biopsy may be done.
If you have chronic hives, your doctor will probably examine you for signs of other medical problems that can cause hives to appear, such as lupus and rheumatoid arthritis. Your doctor may ask for routine tests for these conditions.
Treatment and Prevention
Prevention is the best treatment for hives. If you or your doctor can discover what's causing the rash, you can avoid that trigger in the future. It may be something obvious, but it's possible that you'll never find out.
The itching of hives can usually be rapidly relieved with antihistamines like hydroxyzine* or diphenhydramine. These antihistamines tend to cause drowsiness. Other less sedating antihistamines (such as desloratadine, cetirizine, loratadine, or fexofenadine) may also be used for chronic hives or if acute hives last for more than 24 to 48 hours.
Severe hives or angioedema can be treated with adrenalin injections (sometimes called epinephrine). Adrenaline constricts blood vessels, which reduces swelling. Corticosteroids may be given orally (by mouth) or topically (onto the skin) in extreme cases, but never for very long. Medications called leukotriene modifiers (e.g., montelukast) may be tried in some patients if other medications have failed to work.
These medications can treat the symptoms very effectively, but there's no actual cure. Hives usually clear up within a week, but they can go on for 2 or more years.
A monoclonal antibody called omalizumab may be used if chronic hives persist despite other treatments.
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