Urticaria, a common skin problem, is the medical term for hives. However, the term “hives” is used somewhat loosely in everyday speech. Other terms that are used for urticaria include “wheals” and
“welts.”

What is Urticaria?
True urticaria are raised flat-topped bumps produced by inflammation and swelling in the upper layers of the skin. The hallmark of hives is that they are very itchy. They can be pale to pink to red in color, though skin color can affect their appearance. They are usually 1 to 2 cm in diameter, or about the size of a quarter to a half-dollar coin, but their size is variable. They are typically oval or round but can be more complex shapes. They have distinct edges, but they can merge with each other as they grow, forming larger hives. They look something like mosquito bites without the central puncture mark. Sometimes they occur with inflammation in deeper skin regions, which causes swelling and possibly pain. This deeper swelling is called angioedema.

Hives form within minutes and fade within hours. However, as one hive fades new hives may emerge. In most cases, the hives, if they recur at all, will keep recurring for a few days to a few weeks. This is known as acute urticaria. About 1% of people will get hives that keep coming back for months to years; this is called chronic urticaria. In those patients with chronic urticaria, about half will have resolution or improvement of symptoms within a year.

People of all ages can get hives, including children. About 20% of people will have hives at some point in their lives. Hives are usually benign, if annoying and disruptive, but sometimes they can be part of a serious allergic reaction. In these cases, there will be other symptoms such as abdominal pain, lightheadedness, difficulty swallowing or trouble breathing. Such a broader allergic reaction, called anaphylaxis, is a medical emergency.

Cause
Hives are caused by the activation of mast cells, which are cells involved with the immune system that occur in the skin. When activated, mast cells release many substances that trigger inflammation. One of the main chemicals they release is histamine.

Many of the treatments for hives involve blocking histamine’s effects. Classically, mast cells are
activated via a type of antibody (a protein that binds to specific foreign material triggering an immune
response) that is primarily involved in allergic reactions. Direct mast cell activation by ways other than
allergic reactions can also occur.

Specific triggers frequently are identified in patients with acute urticaria, but only in 10 to 20 percent of the time with chronic urticaria. A particularly common cause in infants and children is recent colds or other infections, which may account for the majority of cases of hives in children.

Allergens (substances that trigger an allergic response) in the air, food, or in direct contact with the skin are another common trigger, as are medications (including antibiotics and medications like ibuprofen).

Sometimes foods will cause hives not through an allergic reaction, but rather because they contain or release histamine. Strawberries and tomatoes are especially known for doing this. If food is the cause, the hives will typically occur within a half hour of eating.

Other causes include insect stings, stinging nettles (a plant), and physical stimuli such as heat, cold,vibration, pressure, water or light (the last two are rare causes). Physical stimuli causing hives may be more common in children than adults, and tends to have a more chronic course. Systemic disease such as hypothyroidism, inflammation of blood vessels, overproduction of mast cells (mastocytosis), viral infections of the liver, and lymphoma (a cancer of the lymph nodes) can be triggers for ongoing
outbreaks, but these are rare causes of hives in children and are seldom the only symptom.

Other conditions can be mistaken for hives. Examples include insect bites, rashes from medications, eczema, skin reactions to irritants, or rashes from viral infections. A physician can usually distinguish
hives from these other conditions by examining the rash and asking questions.

Physicians seeing patients with hives will examine the skin to see the hives for themselves. Because the hives can fade by the time of the doctor’s appointment, taking a picture of them can be helpful. The physician will asks lots of questions to identify what might be the trigger for the hives, and do a physical exam to look for any signs of an underlying disease. Blood tests usually are not needed unless the hives have been coming back regularly for more than six weeks. A biopsy may be done if the individual hives have been there for more than one day or are painful rather than itchy. Other testing such as allergy skin testing may be done if the doctor thinks a specific cause is likely, but they are not routinely performed.

Treatment
As most cases of hives are benign and will resolve quickly, the treatment is focused on controlling symptoms, especially itching. The first medications used are the non-sedating antihistamines such as loratadine (Claritin), fexofenadine (Allegra), or cetirizine (Zyrtec), many of which are available over the counter. The doctor may recommend more than the normal dose, but this should only be done under a physician’s supervision. Sometimes other prescription medicines are added if the first-line medications don’t control symptoms well enough. Other medications that may be added to control symptoms include
older anti-histamines such as diphenhydramine (Benadryl) ranitidine (Zantac) or famotidine (Pepcid) that are normally used for stomach problems, steroids such as prednisolone (Orapred), or medications that block other inflammatory mediators such as montelukast (Singulair). If these medications still do not control the hives, the doctor may consult a specialist.

The best treatment is prevention; if triggers are identified or suspected, avoid exposure to the extent possible. The question has been raised whether avoidance of certain triggers during pregnancy or in early childhood may help prevent later disease. Researchers have looked at all of the studies examining whether avoidance of certain allergenic foods by mothers during pregnancy and use of soy formula versus milk formula might decrease development of various skin problems. Unfortunately, the included data on urticaria are very limited and to date there is no evidence that use of soy formula or maternal avoidance of dietary allergens provides any benefits to children in preventing later occurrence of urticaria.

The vast majority of patients with hives will only have acute urticaria, which is self-limiting. If there are no signs of a broader allergic reaction and the hives are limited, watchful waiting may be appropriate; they will usually fade within a few hours. If the hives are widespread, are particularly troublesome, or keep recurring, a doctor’s visit is appropriate. If the individual hives last for more than a day or are painful, it ay
be something more serious and should be evaluated by a doctor promptly. If there are signs or symptoms of a more serious allergic reaction, seek emergency medical attention immediately.

You may also be interested in:

From issue: 27/07-08