It’s difficult to know the exact risk as it really depends if the person had a sexually transmitted infection (STI) in the first place. The length of time you are exposed does make a difference in your chance of getting an STI. For example if this only happened once for a brief period of time your chance would be much lower than if you had this type of sex on a regular basis.
Also the way you have sex makes a big difference. For example we do not see HIV being passed to people who receive oral sex. Have a look at our “Know your chances” web page, it provides information on your chances of getting or passing an STI depending on how you are having sex. Have a look at the section on oral sex.
Even though it is common for us to see gonorrhea and chlamydia passed when receiving oral sex I think it would be unlikely for it to happen in this situation given there was no fluid to fluid contact. It could be possible for STI like herpes simplex virus (HSV), human papillomavirus (HPV) and syphilis to pass but the chance would be low given the brief contact.
It is also common that many STI do not show symptoms, given this we recommend that people go for STI testing. I would just talk with the health professional you see for your next STI test about your personal situation, they would be able to recommend tests based on your past sexual history.
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