Semen
If a man has a sexually transmitted infection or STI (an infection that is passed from one person to another by sex), the germs that cause the disease can appear in his semen. If the person that the man has sex with touches the semen, he or she can become infected by the germs and pick up the disease. HIV, chlamydia, gonorrhea, hepatitis B, herpes and syphillis are examples of STIs. Human papillomavirus (HPV), which is very common and has many types, can increase the risk of throat cancer. Vaccinating young people (both girls and boys) before the age when they might try oral sex can reduce their risk of contracting HPV. The United States CDC says the HPV vaccine should be given at age 11 or 12 years but says that HPV vaccination can be started at age 9. One of the ways for a man to lower the chance of passing on an STI to his sexual partner is to wear a condom on his penis when having sex. While it is very common for people to use a condom when having sexual intercourse (vaginal or anal sex,) very few people use a condom when having oral sex. Getting semen in your mouth can be bad if the penis or semen has infections, especially you have a cut or sore in your mouth.