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.
The chances of getting or passing an STI can change depending on:
1) The type of STI
3)whether or not steps are taken to lower the chances of getting or passing an STI.
The Categories we've used
i) Commonly passed:
The infection is commonly passed this way
The infection can be passed this way with the right conditions.
iii) Not Commonly passed:
This is not a common way to pass the infection but it may be possible under certain circumstances.
iv) Not passed:
There is no possibility for passing the infection.