Some say it's great and pleasurable. Others say it's a sin and plain disgusting. But both sides can definitely agree on one thing. It's risky.

Many think anal sex is taboo and something that only homosexuals do. But experts say heterosexuals also do it.

Studies have shown that about 50 percent of married men and 25 percent of married women, 18 to 35, have tried anal intercourse at least once, says James C. Achtzehn Ph.D., a retired sexuality professor from Gallaudet University, Washington, D.C.

Unnatural? 

We got a lot of strong, negative reactions when we asked teens about anal sex.

"Anal sex is not what God intended," says Laura, a freshman, in Missouri.

"It is the most disgusting form of sex there is and I wouldn't have anal sex with my girlfriend, even if it meant ending my relationship with her," adds George, 17, of Connecticut.

Why do people react this way? When we think of anything that has the word anal in it we automatically think of waste, explains Achtzehn. This is the main reason why many think anal sex is bad. The penis and vulva are not considered as gross, he adds.

Others, though, think anal sex is OK.

"I personally like doing anal sex on girls," says Kevin, 16, from New York. "But most girls don't like it because they're afraid it's gonna hurt a lot. Some girls are all for it, though. It's not a big deal -- just another way of having sex."

"I think teens try it because guys feel that it is a better sensation. It is definitely more of a guy thing," adds Angel, 17, of New Jersey.

More Risks

Anal sex comes without pregnancy worries -- it's very unlikely a girl can become pregnant through anal sex, unless semen drop out of the anus into the vagina. But, when it comes to STDs, anal sex is much riskier than other types of sex, including oral and vaginal, says
Tracey Adams, community outreach and promotions manager, of the American Social Health Association, which specializes in STD education.

The lining of the anus tears easily during intercourse, making it more likely that sexually transmitted diseases, including the AIDS virus, will be passed on, she explains.

So, if you decide to have anal sex, never, ever do it without using a latex condom! We can't say this loud enough. Condoms help prevent the spread of STDs.

Also, the anus contains bacteria that is healthy there, but harmful in any other part of your body. So, heterosexual couples should never switch from anal to vaginal sex without washing the penis and changing the condom.

Water-based lubricants, like KY Jelly, are another must if you decide to have anal sex. They reduce the chances of tearing anal tissue. Without lubrication, anal sex can really hurt. (Don't use Vaseline because it can cause the condom to break).

Anal sex can also hurt if insertion is too quick, forceful or pressured (meaning you re not really sure want to do it). The anus is a muscle that will tense up when something is being forcefully inserted. That's why many people who experiment with anal sex usually
start by inserting a finger. And sometimes, that's as far as they go.

Be Sure

So now you know about the physical risks. There can also be emotional or mental ones.

Just like with any sexual act, if you are forced into it, or you do it because you think everyone else is, you'll probably ending up regretting it or feeling guilty and ashamed, notes Achtzehn.

"As with other behavior, people shouldn't do it just because others do it -- or someone wants them to do it," he says. "This is very unhealthy. You should not practice anal sex unless you are with a caring partner that you trust -- and you're sure it's something you
want to do."

National correspondents Lindsey Armstrong, Media, Pa., Matthew Cuneo, New Canaan, Conn., Pauline Hemmingway, Bronx, N.Y., and Jenny Bickel, St. Louis, Mo. contributed to this article.