Male condoms are thin protective sheaths that cover the penis or interior walls of the vagina. Condoms are the only contraceptives that also provide protection against sexually transmitted infections (STIs), Hepatitis B and C, and HIV. Condoms provide different levels of risk reduction for different STIs because infections are transmitted through different physiological mechanisms. Some STIs spread by contact with bodily fluids while others are spread through skin-to-skin contact. Research shows that condoms are most effective in preventing STIs spread by bodily fluids, such as bacterial infections like gonorrhea, syphilis, and chlamydia as well as those spread by viruses such as human immunodeficiency virus (HIV). Condoms can also reduce the risk of contracting diseases spread by skin-to-skin contact, such as herpes and human papillomavirus (HPV) if sores are in areas covered by the condom.