What are Hives? – Learn More

So, You’ve Been Diagnosed with Hives!

by Richard S. Roberts, M.D.

Do you really have the Hives?

Don’t despair. You’re not alone. Approximately 20% of the population will have hives (urticaria) at one time or another during their lifetime. First off, are you sure that they’re really hives? True hives are red, itchy, usually raised lesions that look very much like mosquito bites. They are often round or oval but can be  irregularly shaped. Their size may vary from ¼ inch to several inches in diameter. They may blend together. Each spot lasts anywhere from 4-36 hours and is surrounded by normal looking skin. As they resolve the skin looks normal, not flaky or rough. While the hives are present one spot will be resolving while another nearby is developing. In about 40% of cases localized swelling (angioedema) of the lips, eyelids, hands, feet or tongue also occurs.

So, if these are really hives they must be from an allergy, right? Well, unfortunately it’s not that simple and modern science doesn’t have all of the answers. The history of how they first appeared and what’s happened to them since can provide important clues as to what category of hives you have. But first, what actually is a hive? Everyone’s skin is made up of many types of cells. One of these cells is called a mast cell. Everyone’s mast cells make and store histamine. They also routinely make leukotrienes and other substances that can cause localized inflammation. Mast cells don’t usually release much of these substances into the surrounding skin but if they do, these substances, especially histamine produce localized redness, itch and swelling we recognize as a hive or if it’s slightly deeper, angioedema.

Allergy Hives

So, why are my mast cells releasing histamine and other things when they shouldn’t? The first question that needs to be asked is for how long have you had hives? Hives that have been present intermittently or daily for less than 6 weeks are called acute hives, and if longer, chronic hives. Amongst the many possible causes of acute hives those due to allergic reactions get the most attention. In allergic patients the mast cells are coated with an allergy antibody, called IgE, that recognizes a very specific target (peanut, penicillin, yellow jacket, etc.). When that substance, such as peanut, becomes attached to that allergy antibody a chain reaction occurs that activates the mast cell which results in the release of histamine and other inflammatory substances. A hive is born! For food allergy reactions, there are 3 useful rules to consider:

• First, the reaction begins quickly, within 5-30 minutes of eating the food; on rare occasions up to an hour but almost never longer.
• Second, it goes away within a few hours or at the most within a day or two. Therefore, you never get hives for a week from one serving of peanut butter.
• Third, the reaction is reproducible, meaning that if hives were caused by eating 4 peanuts on a Monday, eating 4 peanuts the following week will almost always cause the same problem. Despite popular belief, artificial food colorings and food additives almost NEVER cause hives.

Hives from antibiotics is a different situation. The hive reaction can begin anywhere from a few minutes after the first dose to 10 days after finishing the course. Antibiotic related hives can persist for up to approximately 2 weeks.

Allergic hives from stinging insects are usually obvious but occasionally they can be sneaky by occurring while you’re asleep or distracted. They begin quickly after the sting and resolve in a few hours to a few days. In the U.S. spiders, flies and mosquitoes almost never cause hives although rare cases have been reported.

Almost any medicine or herbal product can potentially cause hives but one of the most common medicines implicated is the aspirin family (aspirin, ibuprofen, naproxen, etc.). Isolated swelling without hives is a unique side effect of the ACE inhibitor blood pressure medicines. Soaps, detergents, fabric softeners almost never cause hives but if they do, the hives occur only where the skin is touched. Airborne allergy to pollen, dust, etc. almost never causes hives unless the person is in the midst of a massive hay fever attack. In an allergic person, direct skin contact with a potent allergic substance like animal saliva or latex can cause hives at the site. All categories of allergic hives are potentially dangerous while chronic hives are usually not.

Chronic Hives

So, if acute hives don’t seem to have an allergic cause what else could be going on? One of the more common presumed causes, especially in children is post-infectious hives. During or within a week of viral, strep or other infections hives may occur through poorly understood mechanisms. This often leads to confusion when antibiotics have been given for the infection. Were the hives from the antibiotic or from the underlying illness? Post-infectious hives can recur for up to 6 weeks. At times, even without infection or any obvious trigger a few hours to a few days of hives occur. These are called acute idiopathic hives. We assume that the immune system is inappropriately activating the skin mast cells but we don’t know why. We don’t think that stress is a common cause.

So, your hives have gone on for more than 6 weeks, so they fall into the chronic urticaria category. Now what? Once again you’re not alone. Approximately 3 million Americans of all ages have the same problem. There are some important things that you should know. The first is that, unlike acute urticaria, less than 5% of the cases are due to some external cause. Also, unlike acute urticaria, the hives and /or swelling are rarely dangerous. In this form of hive problem various quirks and idiosyncrasies of the immune system, as they relate to mast cells, are the primary cause.

Our understanding of the problem is improving but there are many unanswered questions. The best understood of these idiosyncrasies is called chronic autoimmune urticaria. Approximately 45% of all chronic hives are of this type. In this condition the immune system makes a detectable antibody (for which we have a test) that mistakenly thinks that parts of the mast cell surface are the enemy. This antibody attacks the skin mast cells which leads to the release of histamine, etc. It’s been known for a long time that if our body makes one autoantibody type of mistake it’s easier for it to make other autoantibody mistakes. Therefore, it’s not terribly surprising that in chronic autoimmune urticaria approximately 20% of patients, especially women, will also have autoantibodies that target the thyroid gland. This may lead to Hashimoto’s thyroiditis and periodically blood tests for thyroid function should be checked. Unfortunately, treating this thyroid condition probably does not benefit the hives.

The next most common type of chronic urticaria is chronic idiopathic urticaria. This condition is almost certainly due to the immune system’s interaction with mast cells but the details are unknown. Both chronic autoimmune and chronic idiopathic urticaria may worsen during febrile illnesses, with the use of aspirin family medicines, prior to the monthly menstrual period or with sustained pressure to or rubbing of the skin. Individual hives that sting more than itch, leave bruises and last 3 or more days may indicate hives due to vasculitis (inflammation of the blood vessels).

Other forms of chronic hives have to do with the immune system’s reaction to physical triggers. Hives produced by stroking of the skin is called dermographism. Some people’s hives are triggered just by cold, heat, skin pressure, vibration, exercise, sun or even water. These conditions are fairly rare. Some exercise induced patients can either react just to exercise while others react only if their exercise follows the consumption of a food to which they are mildly allergic, most commonly wheat, celery and shellfish. These exercise reactions can produce anaphylaxis and may be dangerous. Another dangerous condition, this one involving angioedema and never hives, is called hereditary angioedema. In these patients swelling of the upper airway can be fatal. Such patients also usually have pronounced abdominal pain from swelling of their intestines. Treatment is available.

So, now that you’ve put your hives into a category how are they treated? For acute hives and rare cases of chronic hives avoidance of triggers is the key. If the acute hives are already present antihistamines and if severe, a short course of oral steroid is used. For chronic hives daily preventative antihistamines are essential. Doses higher than those used for nasal allergy treatment are often needed. If maximum antihistamine dosing has been reached without control, addition of an H2 blocker (e.g. Tagamet) and/or a leukotriene blocker (e.g. Singulair) may be tried. Maximizing the above therapy should minimize the need for oral steroid. Relying on recurrent courses of oral steroids (prednisone) especially without full antihistamine, H2 blocker and anti-leukotriene support is to be discouraged. In rare cases cyclosporin or other immunomodulatory medicines may be added. Once control has been achieved medicines should be continued for several weeks or longer past the last symptoms. Slow tapering can then be attempted.

Conclusion

So, what’s my prognosis Doc?

As noted above:

• Acute hives resolve spontaneously.
• Less than 30% of idiopathic acute hives will go on to be chronic.
• If you have chronic hives that aren’t of the “physical” type at least 50% will resolve in less than a year and another 20% will resolve over the next several years. The “physical” hives tend to be more long lasting.

Research is ongoing in all of these areas. So keep your chin up, take your antihistamine, and get the necessary attention to the type of hives that you have.