Unprotected anal sex ups HIV risk at least 20-fold as compared to unprotected vaginal sex, research shows.
Could the use of lubricants - at least certain kinds - be another risk factor among men and women who engage in receptive anal intercourse? Two studies suggest the answer is yes.
One study involving 879 men and women in Baltimore and Los Angeles, between October 2006 and December 2008, showed that those who used lubricants were three times more likely to have rectal sexually transmitted infections (STIs).
Pamina Gorbach, School of Public Health and the David Geffen School of Medicine at the University of California, Los Angeles, led the study.
Another study that subjected popular over-the-counter and mail-order lubricants -- often used with receptive anal intercourse -- to rigorous lab tests found many of the products contained higher amounts of dissolved salts and sugars compared to what's normally found in a cell.
As a result, the products had toxic effects on the cells and rectal tissue studied. Some of the lubricants caused significant portions of the epithelium - the layer of cells that serves as a protective barrier inside the rectum - to be stripped away.
In the US alone, receptive anal intercourse is practiced in up to 90 percent of gay men, according to International Rectal Microbicides Advocates (IRMA).
Moreover, the practice is not limited to men. US estimates and surveys in Britain indicate between 10 to 35 percent of heterosexual women have engaged in anal sex at least once.
Globally, estimates suggest five to 10 percent of sexually active women have anal sex. While condoms are generally effective for protecting against HIV and other STIs, most acts of anal sex go unprotected.
Microbicides - substances applied topically on the inside of the rectum or vagina - could potentially help prevent the rectal transmission of HIV, and some are being tested in early Phase I safety studies, a University of California, Los Angeles, release said.
The findings were presented at the M2010, the sixth biennial meeting of the International Microbicides Conference May 22-May 25 at Pittsburgh, US.
Nearly 1,000 participants from 47 different countries attended the meeting to hear about the latest developments in HIV prevention research.