Researchers at the Charles R. Drew University of Medicine and Science and the University of California, Los Angeles, have determined through a laboratory study of mouth tissue samples that oral sex does have the potential to transmit HIV, Reuters Health reports. The scientists obtained oral tissue samples from more than 50 HIV-negative adults and exposed the tissue to three different strains of HIV. They found that two of the strains could infect and reproduce within keratinocytes, cells in the outer lining of the mouth, and then proceed to infect T cells deeper in the mouth tissue. However, because the researchers say saliva serves as a natural HIV inhibitor, the keratinocytes were infected at a much lower rate than seen with other body cells--as low as one-quarter to one-eighth the level seen with white blood cells.
Because of this, the risk of HIV transmission through oral sex is much lower than through unprotected anal or vaginal sex, said lead researcher Xuan Liu. The researchers called for additional studies to see if their laboratory findings are duplicated in human trials. There is no consensus on whether oral sex poses a significant risk for HIV infection. Previous studies have suggested that there is a slight risk of infection, while other research has indicated that the risk is virtually zero.