Safer Sex Guide

The chances of getting or passing STIs

For an STI to be passed during sex, one of the partners has to have the infection. It is not always possible to know whether someone has an infection just by looking at them. Some symptoms, such as blisters, warts or sores, can be obvious, but that’s not always the case. Many people with STIs don’t even know they have an infection because they have no symptoms. Even if they do know, they might not be comfortable talking about the infection.

The chances of getting or passing an STI can change depending on:

  • the type of STI
  • the type of sex you’re having
  • whether or not steps are taken to lower the chances of getting or passing an STI

The following charts will help you to better understand the chances of getting or passing an STI, depending on the type of sex you’re having. Having the right information about risk can help you decide what you’re comfortable with. Many STIs are passed in similar ways, but some are more commonly passed than others under certain conditions. Keep in mind that comfort levels can change over time and under different circumstances, but when you have the facts it’s easier to have the sex you want and take care of your sexual health at the same time. The charts are based on sex where no risk-reduction tools are used (for example, using a condom or consistently taking antiretroviral medication to maintain low levels of HIV in the blood and reduce transmission risk). The information is based on the latest research, but they are general estimates only and may not cover every situation.

The categories we’ve used

Commonly passed Can be passed Not commonly passed Not passed
The infection is commonly passed this way The infection can be passed this way with the right conditions This is not a common way to pass the infection but it may be possible under certain circumstances There is no possibility for passing the infection