The fact that you are using your penis to rub your vulva through your underwear does not generally lead to the infection of STDs, but if the other party has an STD, it does not exclude the possibility of being infected, but the chances of infection are smaller. The actual fact is that there are many kinds of STDs, such as genital herpes, warts, syphilis, AIDS, gonorrhea, etc. Different STDs are transmitted in different ways, but most are transmitted through direct contact with sexual intercourse. Of course, there are other ways of transmission, such as syphilis and AIDS, can be transmitted through blood, and individuals can also be infected through contact with each other’s intimate clothing. Therefore, although only rubbing the vagina through the underwear, and no substantial sexual activity, the chances of infectious disease is small, but if the other party exists STDs, their body fluids (semen, vaginal secretions) through the underwear contacted the genital tract or other mucous membrane, especially if the skin in contact with the presence of inflammation or broken, there is also a risk of infection. Therefore, it is advisable to avoid unclean or unprotected marginal sexual intercourse in general.