URTICARIA AND ANGIOEDEMA - KEY FACTS

by Dr Anne Kobza Black, Consultant Dermatologist, St John's Institute of Dermatology, St Thomas' Hospital, London

What are urticaria and angioedema?

Urticaria (hives, nettlerash, welts) is a condition in which short-lived swellings occur anywhere on the body. These swellings (weals) may be pale, pink, or red, of different sizes and shapes and itchy. As the raised weals flatten, they leave red marks which disappear usually in a day. New weals may then appear in other areas. Angioedema is a deeper form of urticaria. These deeper swellings frequently occur in the eyelids, lips and sometimes in the mouth. The swellings may not be itchy and usually settle in a few days. An individual may have either urticaria or angioedema and many people have both.

How common is urticaria?

Urticaria is common and affects 20% of people at some stage of their lives.

What is happening in urticaria and angioedema?

Histamine is released from the skin and causes itching, redness and swelling.

What is the cause?

Histamine release can be triggered by exercise, pressure on the skin and other physical factors as well as foods, drugs and infections. However in the common form of urticaria and angioedema, it is unusual to identify an external cause.

What types of urticaria / angioedema are there?

The most common form is called ordinary urticaria. Other forms called physical urticarias occur sometimes. Less common types include urticarial vasculitis (in which urticaria is due to inflammation of the skin blood vessels) and contact urticaria (in which substances applied to the skin such as fruit, nuts or rubber cause urticaria).

Ordinary urticaria

This is the most common form of urticaria. Weals occur anywhere on the body at any time. Ordinary urticaria is usually divided into acute and chronic forms.

In acute urticaria / angioedema a bout of urticaria usually lasts a few days only. Often no cause can be found but sometimes it may be caused by infections such as a flu infection. Almost any medicine can cause acute urticaria, but antibiotics (especially penicillins) and aspirin are commonly responsible. Sometimes foods may be responsible including nuts, fish, eggs, milk, tomatoes, vegetables and berries.

In chronic urticaria bouts of weals occur daily or almost daily for longer than 6 weeks and a cause is even less likely to be found.

What investigations can be done in ordinary urticaria?

In the vast majority of people no cause can be found though your doctor will ask questions to try to identify one. There is no special test that can reliably identify the cause for urticaria, but some may be done of your answers suggest there may be an underlying cause.

In acute urticaria investigation is usually unnecessary. If an allergic reaction to food is strongly suspected a skin test or a specific blood test may be performed. These and any other tests should be carried out by a specialist in skin or allergic diseases.

It is rare for allergy to be the cause of chronic urticaria so routine allergy tests (skin prick tests) are not necessary. In a small percentage of people foods, colouring agents and preservatives appear to worsen urticaria. A food diary can be kept, and then these substances can be left out of the diet to see if the condition improves and then later deliberately reintroduced. As urticaria is a variable disease the interpretation if these tests is difficult.

What is the treatment?

It is important to avoid anything that may worsen urticaria such as heat, alcohol, aspirin and aspirin containing compounds (paracetamol does not usually cause a problem). Foods, colouring agents and preservatives can be avoided in the rare instances where these have proved to be a problem.

Antihistamines block the effects of histamine and reduce itching and rash in most people, but may not relieve urticaria completely. If urticaria occurs frequently antihistamines are best taken regularly. There are many different types. The older ones often cause drowsiness. However some newer ones are much less likely to cause drowsiness, but are more likely to do so if taken with alcohol. No particular antihistamine is best for everyone, so your doctor may need to try different ones to suit you. Antihistamine tablets may need to be taken for as long as urticaria persists. Reports of serious side effects are rare. However, a few cause weight gain and some should not be taken with certain other medicines.

A related type of antihistamine usually used for stomach ulcers can be added to the histamines used to treat the skin.

If antihistamine tablets are not helpful you can discuss this with your doctor who may arrange for further tests and try other medicines.

Steroids may occasionally be given for a short while for severe flares of acute or chronic urticaria. New treatments which suppress the immune system are being tested in a few most severely affected people in specialist centres and may be beneficial.

Tongue or throat swelling is an unusual, but alarming sign of angioedema which is rarely life threatening except in acute food allergies and the rare hereditary form of angioedema. Sprays or even injections of adrenaline (which can be self-administered) often provide rapid relief.

How long will I have urticaria?

In half the people with chronic urticaria, the rash lasts for 6 - 12 months then gradually disappears. It does not usually recur.

Will urticaria affect my general health?

Although urticaria can be distressing because of itching and appearance it has no direct effect on general health.

Other urticarias
Physical urticarias

Other forms or urticarias (often called physical urticarias) occur in some people and are triggered by physical factors such as heat, light, cold, pressure on the skin and even water. The weals usually appear within minutes and last for less than an hour. Physical urticarias usually occur in healthy young adults and are not uncommon. They may occur in association with ordinary urticaria or with each other and tend to improve with time.

Dermographism ("Skin writing")

Here itching weals occur on rubbing or stroking the skin, which is generally very itchy especially when hot. Weals and red marks often appear as lines and usually last for less than an hour. Usually no cause is found.

Cold urticaria

Cold, including rain, wind and cold water causes itching, redness and wealing in the chilled areas. Swimming in cold water may cause severe wealing and fainting and must be avoided.

Solar urticaria

This is very rare. Redness, itching and wealing occurs in skin immediately after exposure to sunlight.

Aquagenic urticaria

This is extremely rare. Small weals occur on the skin at the sites of contact with water of any temperature.

Delayed pressure urticaria

Swellings occur at skin sites to which pressure has been applied such as from tight clothes or from gripping tools. Usually the swelling develops several hours later. It can be painful and last longer than a day. People with pressure urticaria nearly always have ordinary urticaria as well.

How are physical urticarias treated?

Many of the physical urticarias are improved by avoiding the cause and by regular treatment with antihistamines. Antihistamines do not usually help delayed pressure urticaria. Sometimes a short course of steroids will help if the symptoms of delayed urticaria are very severe.

Cholinergic urticaria (heat bumps)

This occurs under conditions which cause sweating, such as exertion, heat, emotional stress and eating spicy food. Within minutes small itchy bumps with variable redness occur usually on the upper part of the body but may be widespread. The weals usually last for less than one hour, but in severe cases these may join together to form larger swellings. Antihistamines usually help.

Contact urticaria

Various chemicals, foods, plants and animals and animal products can cause weals within minutes at site of contact. These weals do not usually last long. Some of the commoner cause are eggs, nuts (e.g. peanuts), citrus fruits, rubber and contact with cats and dogs.

Urticarial vasculitis

A small percentage of people with urticaria develop weals which last longer that two days. The weals may tender and occasionally bruise. People affected may feel unwell and have joint and stomach pains. This is because their blood vessels have become inflamed (called vasculitis). This is diagnosed by examining under the microscope a small piece of the weal that has been removed. The cause is rarely found though blood tests are undertaken. Antihistamines are not very helpful, but other medicines that help inflammation can be tried. There is a tendency to gradual resolution.

Hereditary angioedema

This is a very rare form of angioedema which tends to run in families. Patients get swellings of the face, mouth, throat and gut leading to colic. The condition is due to an inherited deficiency of blood protein and can be treated by medicines to correct this deficiency. A severe attack of hereditary angioedema can be life threatening if left untreated; therefore patients may be advised to wear a Medic Alert bracelet to alert physicians in an emergency.