Rekindling your first love can have irreversible consequences on your present relationships.

Many adults find it difficult to resist when the sparks fly and they fall again for childhood sweethearts. First loves are indelibly etched into our minds, scientists say, but they warn that rekindling that old flame could have lasting, irreversible consequences, tearing apart marriages and leaving a trail of devastation.

"It's not your average affair" said Nancy Kalish, a California State University-Sacramento psychologist, who has studied such relationships for 14 years. "It goes from the phone to the hotel. It's that quick." Jeannie T. knows the feeling. "It was like lightning struck when we saw each other" she said, after bumping into sweetheart Ben at a 40th school reunion in Joplin, Missouri some months ago.

They hadn't seen each other since Ben waved goodbye on a train platform in 1965 as he shipped off to Vietnam, but as soon as they saw each other again, the sparks flew. "He knelt down at my side and told me that leaving me was the hardest thing he had ever done," said Jeannie, now a Florida real estate agent.

A kind of panic set in, said 60-year-old Jeannie. "I needed to tell him what he meant to me. "However, she missed her chance at the reunion, when Ben's wife of 37 years strolled in on their confession. That's where the Internet came in. Mike T., Jeannie's husband of 13 years, says as soon as his wife returned from the reunion, she and Ben were burning up the Internet, first by email and then via text messaging.

Researchers say their experiences are typical of adolescent sweethearts who fall head-over-heels in love again decades later. Adolescent hormones carve those first loves into our brains, said Rutgers University anthropologist Helen Fisher, author of the book “Why We Love". The lost love's voice or touch triggers wanting, needing, craving in the same spots in the brain as those affected by cocaine.

Sounds like addiction? "It is more powerful than addiction," said Helen. Donna Hanover knows the feeling. After being dumped by her husband Rudolph Giuliani, she found another love, rekindling an adolescent romance after 30 years. She says," I felt an immediate chemistry between us, just as there had been when we were kids". She has published her story with 49 others, including clothing designer Nicole Miller, actors Carol Channing and Suzanne Pleshette in "My Boyfriend's Back".