The downside of 'friends with benefits' - CNN.com
She says it's not just the number of partners at one time; it's that people's behavior seems to be different when they're having "friendly" sex in contrast to romantic sex.
When people have sex with a friend, they tend to be more trusting that the person doesn't have a sexually transmitted disease and therefore fail to use a condom, she says.
"If you've known a person for a while, you don't have that vigilance. You're probably not going to ask them to go and get tested for STDs," Giordano said.
