The cause of all this unpleasantness is usually a highly contagious virus called herpes simplex type 2. (Every once in a while, genital herpes can be caused by the type 1 strain of herpes simplex, a cousin virus that usually infects the mouth, causing blisters and cold sores.

Herpes zoster, which causes shingles and chickenpox, is a different animal.) Although it infects the genitals, type 2 herpes is not necessarily passed through sexual contact. It can be passed from a cold sore on the lip down to the genitals, or from a sore lip to an eye by means of a fingertip. It can ride a wet towel or even a wet fork.

Because the virus is so very contagious, you should avoid all sexual contact during an outbreak. Don't even cuddle. Don't share towels, and if you 've got sores in your mouth, don't share utensils. If you've ever had a genital herpes infection, you should always use a condom during sexual intercourse, even if you can't see any sores.

That's because this crafty virus will begin shedding (making you contagious) for a few days before the sores appear and for a few days after they heal. This means that you may still give your sex partner a valentine of herpes, no matter how hard you try not to. What exactly makes this virus so persistent? It has, it seems, developed a truly ingenious way of protecting itself.

After the first outbreak, the herpes virus retreats to a favorite hiding place in an obscure cranny of the spine called the dorsal nerve root ganglia. There it lies dormant for months or years-even, in some people, forever. For most people who have been infected, periodic herpes outbreaks (usually around the site ofthe original infection) become an unpleasant part oflife. One small consolation prize: Over time, these recurrences usually decrease in frequency and ferocity. It's still not clearly understood what touches off recurrent episodes. Some herpes sufferers say exposure to sunlight, fever, emotional stress, illness or (in women) menstruation increases the likelihood of an outbreak.

But one study suggests the widespread belief that stress touches off herpes outbreaks may be unfounded. In a three-month study of 64 people infected with genital herpes, University of Florida researchers failed to find any connection between emotional stress and later outbreaks. Most ofthe subjects were students, and the researchers noticed dramatic increases in psychological stress on the day before tests and on the day the subjects' herpes broke out. But they found no evidence at all that emotional stress preceded, or touched off, the outbreaks. "These data do not support the popular idea that emotional stress triggers recurrences of genital herpes," the researchers concluded.