Hives often defy explanation.

There are two types of hives: chronic and acute. Chronic hives-have no identifiable cause, can last for days (sometimes weeks and months) and ebb and flare without warning. Acute hives appear suddenly, usually fade quickly and are most likely triggered by an allergic reaction to certain substances, especially, foods.

The good news is, with acute hives, the first outbreak, can be the last-it’s simply a matter of avoiding the trigger. And while you can’t control a flare-up of chronic hives, you can minimize its discomfort-and, even better, take steps to prevent recurrences.

Compared to chronic hives, which can last up to six weeks or longer, most outbreaks of acute hives are sudden and short-lived. And acute hives can explode so fast you may know immediately what caused them. So, if you think those strawberries are responsible for your misery, your doctor can give you a prick test to confirm whether your hives were brought on by allergic reaction.

If acute hives are making you miserable and you’re stumped as to their cause, consider these possible perpetrators.

Food. Shellfish, fish, peanuts, nuts, milk, eggs and wheat can all cause hives. But since food allergies affect only 2 percent of adults, and testing for diet-induced hives is expensive, think before you test. If you experience nausea, vomiting and diarrhea along with the hives every time you eat nuts, wheat or whatever, the problem is apt to be food-induced. If you have hives but no other symptoms, something else is to blame.

Drugs. Penicillin and everyday aspirin are the most common culprits, but even an allergy shot can cause welts. Take a complete inventory of every drug you take over the course of a month, then ask your doctor if there’s a way to eliminate the offender.

Infections. Hepatitis B and mononucleosis can cause hives, too, and so can thyroid and lupus-type diseases, although that’s rare.

Chronic hives are hardly ever from an allergy, but whatever’s causing them can keep them coming back for years. Worse, with chronic hives, all a prick test tells you is what isn’t causing the problem.

If you can’t discover what’s triggering chronic hives, even partial answers are reassuring. While it can be frustrating that you still have the hives, finding out you’re an otherwise healthy person should be helpful because you won’t have to go nuts about keeping food diaries or worrying about an underlying illness.