Hives (urticaria)

         Hives (medically known as urticaria) are red, itchy, raised areas of skin that appear in varying shapes and sizes. They range in size from a few millimeters to several inches in diameter. Hives can be round, or they can form rings or large patches. Wheals (welts), red lesions with a red "flare" at the borders, are another manifestation of hives. Hives can occur anywhere on the body, such as the trunk, arms, and legs.
It is estimated that 5% of all people will develop urticaria at some point in their lives. Hives are more common in women than in men. Of those with chronic hives (those lasting six weeks or more), some 80% are idiopathic, the medical term which means that no cause, allergic or otherwise, can be found.
One hallmark of hives is their tendency to change size rapidly and to move around, disappearing in one place and reappearing in other places, often in a matter of hours. Individual hives usually last two to 24 hours. An outbreak that looks impressive, even alarming, first thing in the morning can be completely gone by noon, only to be back in full force later in the day. Very few, if any other skin diseases occur and then resolve so rapidly. Therefore, even if you have no evidence of hives to show the doctor when you get to the office for examination, he or she can often establish the diagnosis based upon the history of your symptoms. Because hives fluctuate so much and so fast, it is helpful to bring along a photograph of what the outbreak looked like at its worst.
Swelling deeper in the skin that may accompany hives is called angioedema. This may be seen on the hands and feet as well as on mucous membranes (with swelling of the lips or eyes that can be as dramatic as it is brief.)
 Causes 
Hives are produced by histamine and other compounds released from cells called mast cells, which are a normal part of skin. Histamine causes fluid to leak from the local blood vessels, leading to swelling in the skin.
Hives are very common. Although they can be annoying, they usually resolve on their own over a period of weeks, and are rarely medically serious. Some hives are caused by allergies to such things as foods, medications, and insect stings, but the large majority of cases are not allergic, and no specific cause for them is ever found. Although patients may find it frustrating not to know what has caused their hives, maneuvers like changing diet, soap, detergent, and makeup are hardly ever helpful in preventing hives and for the most part are not necessary.
Having hives may cause stress, but stress by itself does not cause hives.
In rare cases (some hereditary, others caused by bee stings or drug allergy), urticaria and angioedema are accompanied by shock and difficulty breathing. This is called anaphylaxis. Ordinary hives may be widespread and disturbing to look at, but the vast majority of cases of hives do not lead to life-threatening complications.
What are the different kinds of hives?
Almost all hives fall into two categories: ordinary urticaria (ordinary hives) and physical urticaria (physical hives).
Ordinary urticaria (ordinary hives)
Symptoms of ordinary hives
Ordinary hives flare up suddenly and usually for no specific reason. Welts appear, often in several places. They flare, itch, swell, and go away in a matter of minutes to hours, only to appear elsewhere. This sequence may go on from days to weeks. Most episodes of hives last less than six weeks. Although that cutoff point is arbitrary, hives that last more than six weeks are often called "chronic."
Causes of ordinary hives
As noted above, many cases of ordinary hives are "idiopathic," meaning no cause is known. Others may be triggered by viral infections. A few may be caused by medications, usually when they have been taken for the first time a few weeks before. (It is uncommon for drugs taken continuously for long periods to cause hives or other reactions.) When a medication is implicated as a cause of hives, the drug must be stopped, since no skin or blood test will prove the connection. In most cases, drug-induced hives will go away in a few days. If a drug is stopped and the hives do not go away, this is a strong indication that the medication was not in fact the cause of the hives.
Some medications, like morphine, codeine, aspirin, and other nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen [Advil]), cause the body to release histamine and produce urticaria through non-allergic mechanisms.
Despite the reputation hives have for being "allergic," when there is no obvious connection between something new that a person has been exposed to and the onset of hives, allergy testing is not usually helpful.

Chronic hives
Chronic hives (defined as lasting six weeks or more) can last from months to years. Allergy testing and laboratory tests are hardly ever useful in such cases.
Physical urticaria (physical hives)

The term physical urticaria refers to hives produced by direct physical stimulation of the skin. By far the most common form is dermographia, which literally means "skin writing." This is an exaggerated form of what happens to anyone when their skin is scratched or rubbed: a red welt appears at the line of the scratch. In dermographia, raised, itchy red welts with adjacent flares appear wherever the skin is scratched or where belts and other articles of clothing rub against the skin, causing mast cells to leak histamine.
Another common form of physically induced hives is called cholinergic urticaria. This produces hundreds of small, itchy bumps. These occur within 15 minutes of exercise or physical exertion, or a hot bath or shower, and are usually gone before a doctor can examine them. This form of hives happens more often in young people.
Other forms of physical hives are much less common. Triggers for these include cold, water, and sunlight.
 Treatment 
The goal of treating most cases of ordinary urticaria is to relieve symptoms while the condition goes away by itself. The most commonly used oral treatments are antihistamines, which help oppose the effects of the histamine leaked by mast cells. The main side effect of antihistamines is drowsiness.
Many antihistamines are available without prescription, such as diphenhydramine (Benadryl), taken in doses of 25 milligrams and chlorpheniramine (Chlor-Trimeton), taken in a dose of 4 milligrams. These can be taken up to three times a day, but because these medications can cause drowsiness, they are often taken at bedtime. Those who take them should be especially careful and be sure they are fully alert before driving or participating in other activities requiring mental concentration.
Loratadine (Claritin, 10 milligrams) is available over the counter and is less likely to cause drowsiness. Also approved for over-the-counter use is cetirizine (Zyrtec, 10 milligrams), which is mildly sedating. Some antihistamines are available in combination preparations with decongestant medication (Claritin-D, Zyrtec-D). The decongestant component is not needed to treat hives.
Antihistamines that require a prescription include hydroxyzine (Atarax, Vistaril) and cyproheptadine, both of which tend to cause drowsiness. Prescription antihistamines that cause little sedation are fexofenadine (Allegra) and levocetirizine (Xyzal). Sometimes physicians combine these with other types of antihistamines called H2 blockers, such as ranitidine (Zantac) and cimetidine (Tagamet). This antihistamine list is not exhaustive. Physicians individualize treatment plans to suit specific patients and modify them depending on the clinical response.
Oral steroids (prednisone, [Medrol]) can help severe cases of hives in the short term, but their usefulness is limited by the fact that many cases of hives last too long for steroid use to be continued safely. Other treatments have been used for urticaria as well, including montelukast (Singulair), ultraviolet radiation, antifungal antibiotics, agents that suppress the immune system, and tricyclic antidepressants (amitriptyline [Elavil, Endep], nortriptyline [Pamelor, Aventyl], doxepin [Sinequan, Adapin]). Evidence to support the benefit of such treatments is sparse. In ordinary cases, they are rarely needed.
Topical therapies for hives include creams and lotions which help numb nerve endings and reduce itching. Some ingredients which can accomplish this are camphor, menthol, diphenhydramine, and pramoxine. Many of these topical preparations require no prescription. Cortisone-containing creams (steroids), even strong ones requiring a prescription, are not very helpful in controlling the itch of hives.