It’s a little more difficult to have sex when you are living with your parents.

A sexual relationship is also perhaps not as enticing when you are online most of the day and access to pornography is so plentiful.

Those are two of the reasons given by researchers for what they have concluded is a decrease in sexual activity among millennials when compared with their Generation X counterparts.

The researchers published their findings today in the journal Archives of Sexual Behavior.

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Less sex, fewer partners

The study was led by San Diego State University psychology professor Jean M. Twenge, Ph.D., the author of the book “Generation Me.”

The team combed over data from 26,707 respondents to the General Society Survey. The data was collected from members of the millennial generation as well as their predecessors from Generation X.

Twenge said the data show the younger adults are having sex less often, and are engaging with multiple partners less often than those from Generation X.

According to the research, 15 percent of people 20 to 24 years of age reported having no sexual partners since they turned 18. That compares with 6 percent of Generation X members who reported no sexual partners when they were young adults.

This finding matches a study last year from the U.S. Centers for Disease Control and Prevention (CDC). The Youth Risk Behavior report stated that 41 percent of today’s high school students reported having had sex, compared with 51 percent of high school students in 1991.

"This generation appears to be waiting longer to have sex, with an increasing minority apparently waiting until their early 20s or later," said Twenge in a press release. "It's good news for sexual and emotional health if teens are waiting until they are ready. But if young adults forgo sex completely, they may be missing out on some of the advantages of an adult romantic relationship."

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Why they’re waiting

Experts have a number of theories on why millennials might be having less sex.

The first is simple logistics.

Twenge noted the increasing number of millennials living with their parents. In fact, a Pew study this year reported 32 percent of the current generation, a higher percentage than any other living arrangement.

There’s also the amount of time millennials spend online. Part of that activity includes the availability of pornography to satisfy some sexual needs, but it also involves the connections millennials feel they have in cyberspace.

"Online dating apps should, in theory, help millennials find sexual partners more easily," Twenge said. "However, technology may have the opposite effect if young people are spending so much time online that they interact less in person, and thus don't have sex."

Some experts worry this online satisfaction is an indication millennials may have trouble forming deep romantic relationships. The experts told The Washington Post millennials may put off sex because of the pressure to succeed and unrealistic expectations created by online images.

Experts also say millennials are quite ambitious and may see sex as an activity that takes away from their professional goals.

“It’s a highly motivated, ambitious generation,” Helen Fisher, Ph.D., a biological anthropologist at Rutgers University, told The Washington Post. “A lot of them are afraid they’ll get into something they can’t get out of and they won’t be able to get back to their desk and keep studying.”

Twenge noted there is also a safety aspect. That includes concerns over personal safety amid widespread reports of sexual abuse on college campuses.

"This generation is very interested in safety, which also appears in their reduced use of alcohol and their interest in 'safe spaces' on campus," Twenge said. "This is a very risk-averse generation and that attitude may be influencing their sexual choices."

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