Syphilis is caused by bacteria called Treponema pallidum. The bacteria can enter your body if you make close contact with an infected sore, normally during vaginal, anal or oral sex, or by sharing sex toys.
It may also be possible to catch syphilis if you are an injecting drug user and you share a needle with somebody who is infected.
Pregnant women can pass the condition on to their unborn babies, which can cause stillbirth or death of the baby shortly after labour.
It is extremely rare for syphilis to be spread through blood transfusions, as all blood transfusions in the UK are routinely screened (tested) for syphilis.
