Allergy

Updated 23 June 2014

Hives or urticaria

Lasting for minutes or days, hives (also called wheals or welts) are large, itchy red bumps on the skin. Hives can also last for a longer period

Urticaria can vary from small bumps, or vary greatly in shape and size (from a pinhead to a frisbee).It may be localized to one part of the body or be widespread. It may start off localized only to spread to other areas of the body with time. Although they more commonly appear on the arms, legs and trunk, they can appear anywhere on the body.

Uticaria usually includes redness of the skin, itchiness, and mild to moderate swelling because of leakage of fluid into the tissues. Hives are generally not an emergency, but when they appear suddenly, spread rapidly and are accompanied by a swollen throat, tightness of the chest, wheezing or difficulty breathing, this indicates a severe allergic reaction that requires immediate medical attention.

Angioedema is a reaction similar to urticaria except there is no redness or itchiness and that it occurs in deeper tissue and is characterised by asymmetrical swelling of tissue. Angioedema is frequently associated with urticaria but the two may occur independently. Itoccurs in around 1 in 3 people with urticaria. Angioedema is not always itchy and can sometimes be painful.

How hives are formed

Underneath the lining of the skin, gut, lungs, nose and eyes are mast cells. Mast cells are specialized white cells with the ability to kill foreign bodies such as worms and parasites.

They also play a central role in allergy. Mast cells contain sacks filled with chemicals, including histamine. These chemicals are released in response to certain external triggers, e.g., allergens, physical causes. Some individuals’ mast cells are unstable and cause urticaria without being triggered by an external factor. When these chemicals are released in small amounts, they cause local itch, irritation and redness of the overlying skin. In larger amounts, they will cause fluid to leak out of blood vessels, resulting in swelling of the skin. When released in massive amounts, it may result in shock (anaphylaxis).

How common is urticaria?

Acute urticaria is said to affect 10%-20% of the population at some time during life. It is not uncommon in childhood, but the greatest incidence appears to be in young adults (15%). Chronic urticaria occurs more frequently in mid-life, especially in women.

What causes urticaria?

There are many causes of urticaria; allergic and non-allergic. In about 90% of people with chronic urticaria, no cause is found even after exhaustive investigations. In acute urticaria the chances of determining the cause are higher. For example, many cases of acute urticaria in children may be associated with a viral, bacterial or parasitic infection. Stress can certainly make established symptoms worse, but is very rarely the direct cause of urticaria.

Allergy-related urticaria

Urticaria that is caused by an allergy is usually due to an allergy to foods, spices, food additives or preservatives, insect stings or drugs. The most common foods that cause urticaria are seafood, berries, nuts, eggs and chocolates (but almost every food has been implicated), and the most common additives are preservatives, nitrates and colourants such as tartrazine. Drugs commonly implicated are over-the-counter medications, antibiotics, aspirin, medicines containing tartrazine, birth control pills and medication for colds. Insect bites, worm infestation and infections also commonly result in urticaria. Contact with dogs, cats, pollens, plants, and blood transfusions may also cause urticaria. Auto immune mechanisms may also be involved (this is where the body becomes ‘allergic’ to itself!)

Some people experience urticaria following exposure to contact with materials such as metals, especially nickel and latex. This is called contact urticaria.

Non-allergic causes

Urticaria that result of a non-allergic origin, occur as a result of various physical agents affecting the skin.The types are:

  1. Dermatographism: This is the ability to 'write on the skin'. If the skin is stroked firmly with a solid object a characteristic wheal and flare reaction occurs. You would be able to read what was “written” on the skin for a prolonged period of time.
  2. Heat-induced urticaria:This is a common form of chronic urticaria (5-7%). It appears as small wheals (1-2 mm in diameter), with large areas of flares around it. It frequently involves the skin of the neck and chest. It is associated with increased body temperature, e.g., after exercise, hot showers and emotional stimuli.
  3. Cold-induced urticaria: Urticaria occurs after exposure to cold, cold objects or cold water. The urticaria is usually localised to exposed areas but sudden total body exposure, as in swimming, may cause a drop in blood pressure and can rarely be fatal.
  4. Delayed-pressure urticaria: Application of deep pressure to the skin produces swelling after 1-5 hours, like sitting on one spot for a prolonged period of time. The area will be deep and tender to touch.
  5. Solar urticaria: Urticaria after sun exposure.
  6. Vibratory urticaria/angioedema: It is an acute short-lived itchy swelling of the skin that occurs within minutes of application of a vibratory stimulus to the skin, e.g., handling a power lawn mower, running, clapping and riding a motor bike. Bumps can be seen within minutes after the stimulus and disappears within an hour. 
  7. Aquagenic urticaria: Brief contact of the skin with water of any temperature causes an immediate urticaria in the area of contact.

Treatment

If an avoidable allergen or any other cause has been identified, avoidance is the most effective treatment. Consult your doctor or dietitian to eliminate these triggers in a health and effective way.

Drug therapy

Antihistamines are the first line medication for acute or chronic urticaria. Some of these are over-the-counter preparations. The newer anti-histamines are less sedating and therefore can be used in the daytime as well. Most of them are long-acting and can be taken once-a-day only. Normal prescribed dosages may not be of benefit and your doctor may often prescribe larger doses or the addition of a second medication. Sometimes a specific anti-ulcer treatment which also has some effect on blocking urticaria may be used. If no relief is obtained a doctor should be consulted.

Papular urticaria

Papular urticaria is a term used to describe crops of grouped, itchy, reddened papules or small blisters. Each bump lasts for 2 - 10 days and may leave behind pigmentation.

The cause is usually insect bites of fleas or mites on cats and dogs. However, a cause may not be found. The human flea, bedbug, mosquito and dog louse can also cause urticaria, but the worldwide flea and bedbug being the most common causes.

It occurs mainly on the "bathing-costume area" – the thighs, buttocks and lower torso. However, the distribution depends largely on the insect responsible; in some cases the forearms, arms and face are affected. Fleas may cause papular urticaria where two to three lesions are seen in a row.

Papular urticaria is rare in the first year of life. It is most common in children between the ages of 2 and 7 years, but may occur in adults. The incidence decreases with age, presumably because one gets less sensitive with each bite. Papular urticaria is frequently seasonal, especially in temperate climates where they are worst in the summer. However, it can occur throughout the year.

The majority of children "outgrow" papular urticaria within 3 - 4 years of its onset. Occasionally, the condition persists into adolescence or adulthood.

Treatment

The treatment involves eliminating the cause of the urticaria, relieving itching, and prevention of an infection.

Examination of bedding and the children's play areas for insects may provide a clue to the cause. If insects are found, they must be eliminated by insect repellant or fumigation, and pets should be washed. These bugs are usually not visible to the naked eye. Hanging the bedding in the hot sun may rid these of the bedbugs.

Your doctor may prescribe a cream or antihistamines to help with the itching. Good skin care is essential for prevention of an infection. For isolated or minor infected lesions, an antiseptic e.g. betadine can be applied. However, antibiotics may be necessary for severe or extensive infection.

Dr Harris Steinman, May 2007

Read more:
Protect yourself against food allergies

Allergy Society of South Africa (ALLSA)

 

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Allergy expert

Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies.

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