She’s been charting hookups between lost loves since 1993, and says the Internet has changed how such stories unfold

It sounds innocent. You get to wondering whatever happened to that special someone you dated in high school or college, so you track her, or him, down online and send an e-mail.

Your old flame is thrilled to hear from you. You chat online, talk on the phone, meet for coffee. And faster than you ever imagined, everything gets out of hand and someone’s marriage is ruined.

“It starts with e-mails,” says Nancy Kalish, a psychology professor at Cal State Sacramento who has studied the phenomenon. “It goes to IMs (instant messages), and the hotel room follows pretty soon afterward.”

Of course, most of them don’t intend to get into trouble when they log on, and not all of them do.

“People are just surfing the Internet on a whim,” Kalish says. “They may see some lost love and they say, ‘What the heck’ and send an e-mail.”

Sound familiar? If so, you are not alone. Reunion was created in 2002, says site spokeswoman Shari Cogan, and its growth has been “just unbelievable.” The site has profiles for 34 million people, and is gaining as many as 40,000 daily, she says.

And Reunion is just one of several sites that make it easier than ever to track down an old friend. Classmates allows users to “leap through a portal to the best of your past” and boasts a database of 60 million people who graduated from more than 200,000 schools.

So it’s never been easier to look up and hook up with chat avenue an old crush. But if you’re in a relationship, Kalish has three words for you.

“I wouldn’t touch it if you are married,” she says. “Some of these people have no idea what they are getting into.”

Her research on the subject, which began in 1993, led to her 1997 book, “Lost & Found Lovers

Kalish has made “rekindled romances” her specialty. ” She has appeared with Oprah Winfrey and on “,” and frequently presents her findings at psychological conventions.

Take Amy Altschul, a 54-year-old freelance editor who contacted an old flame after at least 30 years. The two exchanged e-mails, then phone calls.

“Then we got together, and we started seeing each other every single day,” Altschul says. “It was like instant trust, instant like, instant friendship. It was like an addiction or something.”

That’s not uncommon, says Kalish. Old flames often rekindle, she theorizes, because a physical, chemical imprinting occurs when we meet our first love. It typically happens when we are young and impressionable.

Kalish says her research has shown that a vivid dream about an old flame is the most common trigger of the urge for a reunion. Her subjects often interpret such dreams as a sign that they should contact their first love, but Kalish says such dreams speak to the power of those memories.

“These are good people mostly,” she says of those who looked up past loves and wound up pursuing a renewed relationship. “They aren’t looking for trouble. It seems safe. Very few people expected a romance.”

But often, that’s exactly what happened. Old flames meet, they reconnect instantly and powerfully, and before long the situation has run away from them.

Nowadays, about 8 in 10 people who contact a former lover are married, Kalish says, based upon the findings of her own Web site, Lostlovers

Old flames rekindling is nothing new, of course. But the typical story used to be of high school sweethearts, perhaps widowed or divorced, finding each other after decades apart.

That was before the Internet. In those days, Kalish says, tracking down a lost love was hard work, requiring hours on the telephone calling old friends, friends of friends, relatives. The digital revolution changed all that. What used to take days can be done in minutes, and anonymously.

Between 1993 and 1997, Kalish says, about 30 percent of those who reached out to an old flame were married.

No wonder it can be tough finding people willing to discuss their experiences. Kalish says visitors to her Web site often are willing to share their stories, just so long as they don’t have to give their names — even though, as a psychologist, Kalish is required not to disclose their identities.

We ran into the same problem. We queried 1,500 readers about the topic by e-mail. We received very few responses, which seemed odd until the confidential replies started trickling in, each asking “What if you are married?”

Not every contact leads to a torrid, marriage-wrecking romance. But some do. And even if neither person is married, things may take an unexpected turn. After the initial euphoria of getting together with her former beau in e and distanced herself from him.

“I think he’s crazy — seriously insane,” she says now. “Yes, I would do it again, but I would be much more cautious next time.”