The terms sexually transmitted disease (STD) and sexually transmitted infection (STI) are very similar, and both appear in sexual health literature regularly. However, these terms are not identical.

The main difference between an STD and an STI is that an STI may not alter the normal function of the body at first. For example, herpes can infect the body without causing any symptoms, and the infection is only classified as a disease when it becomes symptomatic. Some sexual health experts prefer STI for this reason; it refers to any infection passed from one human to another via sexual intercourse, not just the infections with symptoms.

The two definitions overlap significantly. Some people use them interchangeably, but it is important to note that some infections will not necessarily result in a disease. For example, human papillomavirus (HPV) is the virus that causes genital warts, and according to the CDC, about 20 million Americans are infected. It is an extremely common infection, and the CDC estimates that 50 percent of sexually active people will become infected “at some point in their lives.”

At any given time, however, only about 1 percent of sexually active adults in the United States have genital warts. Therefore, there is a high rate of HPV infection in the United States, but a significantly lower rate of disease. In this case, the STI is much more common than the STD.

Some common STDs and STIs include gonorrhea, syphilis, pubic lice, yeast infections, chlamydia, HIV and the aforementioned HPV. These disease spread through unprotected sexual contact, and sexually active people can greatly reduce the chance of infection by using condoms and dental dams during sex. Condoms do not necessarily protect against every type of sexually transmitted infection, but the CDC notes that latex condoms provide a practically impermeable barrier for pathogen-sized particles. Condoms must be used correctly in order to significantly reduce the chances of a sexually transmitted infection.

There is some evidence that personal lubricant products can decrease the chances of infection during anal, oral and vaginal sex by preventing tissue damage, thereby preventing direct contact with the bloodstream during penetrative sex. Some additives such as nonoxynol-9 may also affect the chances of infection, but the research is unclear as to whether these additives have a positive or negative effect on transmission. The most important factors in prevention are regular condom use and STI testing.