Symptoms can last anywhere from minutes to months - or even years.

While they resemble bug bites, hives (also known as urticaria) are different in several ways:

• Hives can appear on any area of the body; they may change shape, move around, disappear and reappear over short periods of time.
• The bumps - red or skin-colored “wheals” with clear edges - usually appear suddenly and go away just as quickly.
• Pressing the center of a red hive makes it turn white - a process called “blanching.”

• Chronic hives occur almost daily for more than six weeks and are typically itchy. Each hive lasts less than 24 hours. They do not bruise nor leave any scar.

  If your hives last more than a month or if they recur over time, see an allergist, who will take a history and perform a thorough physical exam to determine the cause of your symptoms. A skin test and challenge test may also be needed to identify triggers.

  Therapies range from cool compresses to relieve itching to prescription antihistamines and other drugs, such as anti-inflammatory medications and medications that may modify your immune system.

  Is It Hives or Angioedema?

  Angioedema - swelling of tissue beneath the surface of the skin - can be mistaken for or associated with hives. It can be caused by allergic reactions, medications or a hereditary deficiency of some enzymes. The following symptoms may indicate angioedema:

  • Swelling in the eyes or mouth
  • Swelling of the hands, feet or throat
  • Difficulty breathing, stomach cramps or chemosis (swelling of the lining of the eyes)

  An allergist can diagnose and treat both hives and angioedema.

  Diagnosis

  In some cases, the trigger is obvious - a person eats peanuts or shrimp, and then breaks out within a short time. Other cases require detective work by both the patient and the physician because there are many possible causes. In a few cases, the cause cannot be identified.

  A single episode of hives does not usually call for extensive testing. If a food allergy is suspected, consider keeping track of what you eat. This will help you discover whether there is a link between what you’re eating and when you break out with hives.

  Chronic hives should be evaluated by an allergist, who will ask about your and your family’s medical history, substances to which you are exposed at home and at work, exposure to pets or other animals and any medications you’ve taken recently. If you have been keeping a food diary, show it to your allergist.

  Your allergist may want to conduct skin tests, blood tests and urine tests to identify the cause of your hives. If a specific food is the suspected trigger, your allergist may do a skin-prick test or a blood test to confirm the diagnosis; once the trigger is identified, you’ll likely be advised to avoid that food and products made from it. In rare instances, the allergist may recommend an oral food challenge - a carefully monitored test in which you’ll eat a measured amount of the suspected trigger to see if hives develop. If a medication is suspected as the trigger, your allergist can conduct similar tests, and a cautious drug challenge - similar to an oral food challenge, but with medications - may also be needed to confirm the diagnosis. Because of the possibility of anaphylaxis, a life-threatening allergic reaction, these challenge tests should be done only under strict medical supervision, with emergency medication and equipment at hand.

  In cases where vasculitis may be the cause, your allergist may conduct a skin biopsy and send it to a dermatopathologist to examine under a microscope.

  The cause of chronic hives is often difficult to identify.

  Chronic 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.

  Physical urticaria

  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.Urticaria – also known as hives, weals, welts or nettle rash – is a raised, itchy rash that appears on the skin. It may appear on one part of the body or be spread across large areas. 

  The rash is usually very itchy and ranges in size from a few millimetres to the size of a hand.

  Although the affected area may change in appearance within 24 hours, the rash usually settles within a few days.

  

  Doctors may refer to urticaria as either:

  • acute urticaria – if the rash clears completely within six weeks
  • chronic urticaria – in rarer cases, where the rash persists or comes and goes for more than six weeks, often over many years

  A much rarer type of urticaria, known as urticaria vasculitis, can cause blood vessels inside the skin to become inflamed. In these cases, the weals last longer than 24 hours, are more painful, and can leave a bruise.

  What causes urticaria?

  Urticaria occurs when a trigger causes high levels of histamine and other chemical messengers to be released in the skin. 
  
  These substances cause the blood vessels in the affected area of skin to open up (often resulting in redness or pinkness) and become leaky. This extra fluid in the tissues causes swelling and itchiness.

  Histamine is released for many reasons, including:

  • an allergic reaction – such as a food allergy or a reaction to an insect bite or sting
  • cold or heat exposure 
  • infection – such as a cold
  • certain medications – such as non-steroidal anti-inflammatory drugs (NSAIDs) or antibiotics

  However, in many cases of urticaria, no obvious cause can be found.

  Some cases of long-term urticaria may be caused by the immune system mistakenly attacking healthy tissue. However, this is difficult to diagnose and the treatment options are the same.

  Certain triggers may also make the symptoms worse. These include:

  • drinking alcohol or caffeine
  • emotional stress
  • warm temperature

  Read more about the causes of urticaria.

  Diagnosing urticaria

  Your GP will usually be able to diagnose urticaria by examining the rash. They may also ask you questions to find out what triggered your symptoms.

  If your GP thinks that it's caused by an allergic reaction, you may be referred to an allergy clinic for an allergy test. However, if you've had urticaria most days for more than six weeks, it's unlikely to be the result of an allergy.

  You may also be referred for a number of tests, including a full blood count (FBC), to find out whether there's an underlying cause of your symptoms.

  Read more about diagnosing urticaria.

• Treating urticaria

  In many cases, treatment isn't needed for urticaria, because the rash often gets better within a few days.

  If the itchiness is causing you discomfort, antihistamines can help. Antihistamines are available over the counter at pharmacies – speak to your pharmacist for advice.

  A short course of steroid tablets (oral corticosteroids) may occasionally be needed for more severe cases of urticaria.

  If you have persistent urticaria, you may be referred to a skin specialist (dermatologist). Treatment usually involves medication to relieve the symptoms, while identifying and avoiding potential triggers.

  Read about treating urticaria.

  Complications of urticaria

  Around a quarter of people with acute urticaria and half of people with chronic urticaria also develop angioedema, which is a deeper swelling of tissues.

  Chronic urticaria can also be upsetting and negatively impact a person's mood and quality of life.

  Angioedema

  Angioedema is swelling in the deeper layers of a person's skin. It's often severe and is caused by a build-up of fluid. The symptoms of angioedemacan affect any part of the body, but usually affect the:

  • eyes
  • lips
  • genitals
  • hands
  • feet

  Medication such as antihistamines and short courses of oral corticosteroids (tablets) can be used to relieve the swelling.

  Read more about treating angioedema.

  Emotional impact

  Living with any long-term condition can be difficult. Chronic urticaria can have a considerable negative impact on a person's mood and quality of life. Living with itchy skin can be particularly upsetting.

  One study found that chronic urticaria can have the same negative impact as heart disease. It also found that one in seven people with chronic urticaria had some sort of psychological or emotional problem, such as: 

  • stress
  • anxiety
  • depression

  See your GP if your urticaria is getting you down. Effective treatments are available to improve your symptoms.

  Talking to friends and family can also improve feelings of isolation and help you cope better with your condition.

  Read about how talking to others can help.

  
  
  
  

  Anaphylaxis

  Urticaria can be one of the first symptoms of a severe allergic reaction known as anaphylaxis.

  Other symptoms of anaphylaxis include:

  • swollen eyes, lips, hands and feet
  • feeling lightheaded or faint
  • narrowing of the airways, which can cause wheezing and breathing difficulties
  • abdominal pain, nausea and vomiting 
  • collapsing and becoming unconsciousness

  Anaphylaxis should always be treated as a medical emergency.

  Call 999 immediately and ask for an ambulance if you or someone else is experiencing anaphylaxis. Tell the operator about your (or their) symptoms.
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