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What is hives?
Hives is a skin rash characterised by red patches and itchy swellings on the skin, known as wheals (also spelled weals). These swellings, which look like mosquito bites, can range in size from a few millimetres to several centimetres. Sometimes hives may be accompanied by deeper swelling (angioedema) of the lips, eyelids, hands or other areas.
Symptoms can appear anywhere on the body, but most commonly occur on the trunk, arms, legs, throat and lips. In some cases, hives may last for weeks, but usually the swellings reduce within a few minutes to a few hours. Temporary symptoms occur in about one in 30 children and one in five adults, while chronic hives develop in one in 1000 adults. 
Hives can be triggered by a range of factors, including an allergic reaction, insect stings or bites, infection, or certain foods or medications. If you are prone to hives, contact with one or more of these factors may cause the release of a natural chemical called histamine. This increase in histamine levels causes fluid to leak from blood vessels in the surface of the skin. The end result is inflammation and swelling.
The medical name for hives is 'urticaria', which is taken from a common European stinging nettle (Urtica dioica) known to trigger hives in some people. For this reason, the condition is also sometimes known as 'nettle rash'.
This process is part of the body's normal way of defending itself against potentially harmful organisms, such as bacteria and viruses. However, in hives, this reaction occurs in response to substances or products that may be encountered during everyday life.
Although the cause of histamine release is often unknown, some factors that are known to trigger hives or make symptoms worse in some people include:
- Alcohol and caffeine;
- Animal fur;
- Perfumes, cosmetics and dyes;
- Certain foods, including nuts, fish, cheese, eggs, oranges, chocolate and strawberries;
- Certain food additives, including amines, tartrazine (E102) and benzoates (E210-220);
- Certain medications, such as some vaccines, pain-relief medications, aspirin and antibiotics;
- Insect stings and bites from bees, wasps, sandflies, mosquitos and fleas;
- Certain plants, including nettles and poison ivy;
- Infection with bacteria, viruses (especially upper respiratory) or parasites;
- Exercise, heat or sweating;
- Exposure to cold conditions, including wind, water or rain;
- Long-lasting pressure applied to the skin, and;
- Sunlight or water of any temperature (in rare cases).
Risk factors that increase the likelihood of developing hives include:
Hives is usually classified according to its cause and the time it takes to clear. However, it is also possible for the different types to overlap or occur together. In general though, there are two major types of hives: ordinary and physical.
Ordinary hives is the most common form of the condition. It can appear anywhere on the body and often develops suddenly and for no obvious reason.
Physical hives is usually triggered by an item or situation you may come across in daily life, such as pressure, sweat, cold or a particular substance. Swellings take about five minutes to develop and generally last no longer than 30 minutes.
These two types can be further classified as follows:
Acute hives describes cases that last less than six weeks, although most cases usually only last for 1-2 days. It is also possible for acute hives to return over time. This type is sometimes triggered by an allergic reaction to certain foods or medications, bee or wasp stings, or contact with particular substances, such as latex. For an allergic reaction to occur, you must have previously developed an immune response to a particular trigger.
However, hives is usually not caused by an allergy. Rather, it generally occurs after exposure to certain substances, previous exposure to which did not cause a reaction. Some common causes include infection with a bacteria or virus, or a non-allergic response to certain medications or foods. For example, some medications (e.g. antibiotics, aspirin, codeine and vaccines) and food additives can naturally trigger the release of histamine in the skin without causing an allergic reaction.
Chronic hives describes cases that last for more than six weeks. It is more likely to occur in adults than in children and in many instances, the cause is unknown. When the cause is unknown, the medical name for the condition is chronic idiopathic hives.
Chronic hives is often thought to be the result of an autoimmune response, in which the immune system reacts to triggers as if fighting an infection or healing a wound. The condition is also associated with other autoimmune disorders, such as thyroid disease, coeliac disease and lupus. Chronic hives is relatively uncommon compared with acute hives.
Dermographism (or dermatographism) translates as 'skin writing'. As the name suggests, this type of hives occurs on areas of the skin that have been firmly stroked. Swelling tends to appear where clothes or furniture touch the skin, particularly if you are upset or hot. Dermographism can also occur after showering and then rubbing the skin with a towel. It is usually itchy, starts suddenly and gets worse with scratching.
This relatively uncommon type of hives results from sweating and is sometimes called 'heat bumps'. Sweating may arise from exercise, heat, fever or eating hot or spicy foods. Swellings are very small and circled by a red ring (flare). Cholinergic hives usually develops within a few minutes of sweating and tends to last for about 30 minutes to an hour. It usually occurs on the chest, back and arms in young adults.
Cold hives occurs on skin that is warming up after exposure to cold, including wind, water or rain. If large areas of skin are exposed, the condition can cause extensive swelling and fainting. People who get cold hives are advised not to swim alone.
Pressure hives can occur on its own, but often develops together with chronic hives. This condition may develop immediately after pressure is applied, or more commonly, about 4-6 hours afterwards (delayed pressure hives). Swelling results from long-lasting pressure applied to the skin and tends to last for several hours to a day. It may arise from wearing a tight seatbelt, or gripping a tool at work for extended periods of time.
Contact hives occurs when a trigger substance is absorbed through the skin. Symptoms may be the result of an allergic reaction or a natural response to a toxic agent. Symptoms may occur at the site of contact or elsewhere on the body.
Water contact hives
Water contact hives is also known as aquagenic hives. This condition is rare and usually develops on skin that has been exposed to water at any temperature.
Solar hives develops within minutes of exposure to sunlight or ultraviolet (UV) light from an artificial source. This type of hives is very rare.
Signs and symptoms
Hives is characterised by raised swellings that can vary in size from a few millimetres to several centimetres across. Symptoms vary from person to person, but commonly include:
- Red or pale swellings (wheals) with red margins (flares);
- Raised areas of skin, arising from the joining together of multiple swellings;
- An itching, burning or stinging sensation;
- Joining together of one or more swellings;
- Red margins that remain for up to a day after swellings have flattened;
- Return of swellings at the same or different sites, hours or days later, and;
- Deeper swelling (angioedema) of the lips, eyelids, hands or other areas.
Methods for diagnosis
Your doctor will usually diagnose hives by looking at your skin and asking about symptoms, medical history and any family members with an allergy or skin condition. To figure out what is triggering symptoms, a doctor may suggest keeping a food diary, or removing certain foods from your diet.
Sometimes, hives can be easily recognised and the cause identified without any tests. However, if further investigation is needed, your doctor may conduct a skin prick test or patch test. These tests involve applying substances to the skin of the back or arms and then looking for signs of a reaction. A blood or stool sample may also be taken to rule out other causes.
Types of treatment
One of the main goals in treating hives is identifying and then avoiding any known causes. However, when symptoms do occur or the cause is unknown, your doctor may recommend one or more of the following treatment options:
If you have hives, your doctor may suggest avoiding exercise, hot showers or other activities that produce heat and sweating. Other lifestyle changes may include cutting out alcohol, caffeine, or certain foods. Applying calamine lotion or a cold compress may help to relieve itching and pain. Avoiding medications such as aspirin and codeine, which are known to trigger hives in some people, may also be recommended.
If further treatment is needed for severe itching or symptoms that do not clear on their own, your doctor will most likely prescribe an antihistamine medication. As the name suggests, antihistamines work by blocking the immune response that causes the release of histamine into the skin.
Some examples of antihistamine medications include loratadine, fexofenadine and cetirizine. Alternatively, you may be prescribed a 'sedating antihistamine', such as promethazine, cyproheptadine or diphenhydramine. As these medications also cause drowsiness, they may be recommended for use at night. Antihistamine medications are also sometimes known as 'H1 blockers'.
In some cases, ranitidine, or another member of the 'H2 blocker' family of medications may be added as an extra treatment. These medications also block the activity of harmful histamine, but as they work in a different way, they are not technically classed as antihistamines.
Your doctor may prescribe a medication such as doxepin from the 'tricyclic antidepressant' family of medications. Although these medications are most commonly used to treat depression, they are also thought to help with hives by blocking the effects of histamines. These are usually only prescribed when treatment with antihistamines has not worked.
If symptoms are severe or do not respond to antihistamine medications, your doctor may prescribe an oral corticosteroid medication, such as prednisone. Corticosteroids reduce the body's overall immune response, including the swelling and inflammation seen in hives. However, they are not usually prescribed for more than two weeks, as long-term side effects can include high blood pressure (hypertension), eye problems, thinning of the skin, weight gain and diabetes.
In some cases, a family of medications known as leukotriene inhibitors may be recommended. Although these medications are most commonly prescribed for asthma, they can also relieve the symptoms of hives. Leukotriene inhibitors can be more suitable for long-term treatment than corticosteroid medications, as they produce less side effects. Some examples of these include montelukast and zileuton.
Rarely, powerful immunosuppressant medications such as cyclosporin may be prescribed to reduce general swelling and inflammation. Immunosuppressants work in a similar way to corticosteroids by turning down the body's overall immune response. These medications are usually taken orally.
Although hives is usually quite harmless, sometimes deep swelling or a serious allergic reaction can occur. Seek urgent medical attention if either of the following complications occur:
Sometimes hives can occur together with a build-up of fluid and swelling deep within the skin, known as angioedema. This deep swelling often occurs suddenly and lasts 1-3 days.
Angioedema can occur anywhere on the body, but most often affects the eyelids, lips, hands, feet and genitals. In addition to the visible swelling, angioedema may also cause a painful or burning sensation, problems with vision or swelling of the tongue, throat or airways.
Although quite uncommon, angioedema is more likely if you have chronic hives that lasts for six weeks or more. It can also be triggered by a class of high blood pressure medications known as ACE inhibitors. Angioedema is usually treated in a similar manner to hives, with oral antihistamine or corticosteroid medications.
In very rare cases, hives can develop into a life-threatening allergic reaction, known as anaphylaxis. Signs of anaphylaxis may include a racing heart, dizziness, difficulty breathing, or swelling of the face, lips or tongue. Anaphylaxis is treated urgently with an injection of adrenaline. If this reaction has occurred previously, your doctor may recommend that you always carry an adrenaline pen device with you for injection on the spot. Similarly, swimming or exercising alone is not recommended if you have developed a severe reaction to cold or physical activity in the past.
In most cases, hives may be itchy or painful, but usually fades within 1-2 days without causing any long-term harm. Ongoing cases of chronic hives are uncommon, but may cause distress and sleeping problems, particularly if itching is constant. If treatment is needed, hives can usually be well managed by avoiding known causes and treatment with antihistamine medications.
Hives is usually only potentially dangerous when it occurs with deep swelling (angioedema) or a serious allergic reaction (anaphylaxis). Quite often though, hives is a one-off event and the cause is never identified.
While hives cannot be prevented from occurring in the first place, future cases may be avoided by identifying and avoiding any triggers. Lifestyle changes during a case of hives may also help to prevent symptoms from returning. For example, it may be helpful to avoid excessive exercise, hot showers or other activities that produce heat and sweating. Other changes could include cutting out alcohol, caffeine, or certain foods in consultation with your doctor.