Thousand of students gathered on Stanford's quad for one of the strangest traditions in higher education, kissing underclassmen under the first full moon of the academic year.

Even more strange is that the event is officially recognized and sanctioned by the school, the New York Times reported. Its origin is unknown and its health risks serious, but it still happens every year.

Some said Full Moon on the Quad began in the 1800s when male seniors presented female freshmen with roses. However, some 40-year-old graduate students had never heard of the event. In 1988, it made its transition from "folklore" to an officially sanctioned event.

"It was folklore," said Julie Lythcott-Haims, one of the student officers who helped make the event formal. "We took it off the shelf and dusted it off. We had roses, a string quartet, maybe some champagne. A couple of hundred students showed up."

Dr. Ira M. Friedman, director of the Vaden Student Health Center, said after the school could not put an end to the event, he has worked to make it as safe as possible.

"We try to create an environment in which they don't feel they must participate in the exchange of oral secretions," he said, stressing the importance of consent by kiss recipients.

The annual event is a potential breeding ground for the flu and for mononucleosis (more commonly known as mono, the "kissing disease"). In fact, one of the tips dolled out to freshmen attending the event is to not kiss the school's mascot "the Tree," as he/she always receives the most kisses, hence the most bacteria.

Safety precautions include slogans like "consent is sexy" and "beat Cal," to give the event some school spirit. Attendees are discouraged from brushing their teeth or flossing, as that creates microabrasions in the gums for bacteria to seep in. Instead, mouthwash and mints are recommended and handed out. Any wishing to attend must present their student ID and must report truthfully if they have cold symptoms; any who do are asked to observe and not participate.

The event includes a band and other types of entertainment for those who want to attend, but would rather not participate.

This year, it was not held on the first full moon of the academic year, but on Oct. 22, due to the conflict in scheduling with Homecoming. In the past, the event has been cancelled once: in 2009, the year of the "swine flu" outbreak.

"We decided we couldn't live with the risk," Dr. Friedman said, noting he took into account several East Coast schools reporting outbreaks. "So we made a very unpopular decision."

Francisca Gilmore, a freshman in 2009, said she got the flu that year, a strep throat twice after returning to the event every year since.

"The repercussions were brutal, and I wish I had done better on the Econ 1A final I took later," she said. "But I think in the long run, getting to tell people I've kissed over 50-plus people in a night is worth it."