Since its founding in 1995, the free classified-ad Web site Craigslist has made it much simpler to find bargains on vintage clothes, used furniture and LPs. According to researchers at New York University’s Stern School of Business, the site also provides easy access to something way less cool: sexually transmitted diseases.

“The entry of Craigslist produces a transformative shift in casual sex-seeking behavior,” Jason Chan and Anindya Ghose write in “Internet’s Dirty Secret: Assessing the Impact of Technology Shocks on the Outbreaks of Sexually Transmitted Diseases.” The authors link the site to a 14 percent increase in the rate of new AIDS cases, or more than 6,500 new infections each year, and a similar increase in syphilis infections. “The ease of seeking sex partners through Craigslist’s personal ad listings [has] brought a culture of sexual openness to the younger generation not seen since the seventies,” they write.

Though the study’s data predate Craiglist’s voluntary closure of its “adult services” section in 2010, Chan and Ghose say that its personal ads — available elsewhere on the site — trump the traffic of other singles services such as and eHarmony. Because Craigslist is geographically specific, Chan and Ghose were able to compare STD rates before and after its appearance in 50 states and the District of Columbia. The site brought more promiscuity — and more infection — to most places it appeared.

“The ease of posting feeless ads requesting . . . casual sex encourages the development of promiscuous behaviors within locations served by Craigslist,” they write. One 32-year-old newspaper editor, they note, placed an ad declaring December 2002 to be a “moral free zone” for her; she received responses from 70 men and met up with 10.

“The case of Craigslist’s entry leading to more STD infections serves to show that market participants exert little regulation over their casual sex behavior despite the known health risks involved,” they conclude. Craigslist did not respond to requests for comment.

Chan and Ghose don’t offer immediate solutions to the problem. After all, as Chan pointed out in an interview, if Craigslist closed down, solicitation would just move to another site. “The issue has to do with instant gratification,” he says. “The platform itself probably encourages such behavior, but the individual themself has to make the right choices.”

Justin Moyer