The best way to prevent a sexually transmitted infection (STI) is to wear a condom. For the sexually active, STIs are just another reason to practice safe sex, whether it's oral, vaginal, or anal. STIs can occur throughout the body, including the mouth, vagina, and even the anus.

In the U.S., among men and women between 15 to 44 years old, about 39 percent and 33 percent have engaged in anal sex, respectively. Unprotected anal sex is considered to be the riskiest of sexual activities, whether it’s practiced by gay or straight couples, when it comes to STIs. This is because the anus is not self-lubricating and 40 percent thinner than vaginal tissue, making it more prone to fissures and injury, according to The Center For Sexual Pleasure & Health. Its physical structure makes it easy for STIs to make their way into the bloodstream.

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Dr. Amesh A. Adalja, a board certified infectious disease physician at the University of Pittsburgh, says STIs commonly do affect the anus, especially for those engaging in anal penetration. "Herpes and HPV are likely the most common form of infections acquired this way," he told Medical Daily.

HPV is more common than herpes; nearly all sexually active men and women get it at some point in their lives. A 2009 study published in the Journal of Infectious Diseases found anal infections of HPV appear to be as common as cervical infections. This is alarming since anal HPV infection is strongly linked with anal cancer.

Other STIs normally found in the anus include: gonorrhea, chlamydia, syphilis, lymphogranuloma venereum (LGV), chancroid and donovanosis.

There are some anal STIs that are more detectable than others. For example, herpes is spotted via multiple painful ulcerations with vesicles, according to Adalja. However, gonorrhea and chlamydia, common STIs, are not as easy to spot.

"These infections may not have visible external lesions and could be difficult to visualize. Anal chlamydia and gonorrhea infections may not have even any symptoms," he said.

Tests for gonorrhea, chlamydia, and many other STDs try to identify the pathogen that causes the disease, rather than the body's response to it. However, these tests will not always be able to detect an STI contracted via anal penetration, which is one of the biggest anal sex risks.

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Standard testing for anal STIs include an anal Pap smear, as well as swabs of the rectum, in order to identify any bacterial STIs that are normally transmitted during unsafe anal penetration. Adalja suggests to see a physician after high risk sexual exposure, the appearance of ulcers or lesions, anal or rectal pain, anal or rectal discharge, or anal or rectal bleeding.

Engaging in receptive anal sex, especially those who are immunosuppressed with a condition such as HIV/AIDS, represents the highest risk.

Prevention is the best invention when it comes to health. If you’re having anal sex, talk to your doctor about special testing for anal STIs. They are difficult to detect during standard screening exams, especially if doctors don’t know their patients are at risk.

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