Syphilis is caused by an infectious bacteria. The bacteria enters the body during close body contact through small breaks in the skin.

During sex syphilis can be passed on through any close body contact. Syphilis isn’t just passed on through penetrative sex. It can also be transmitted through skin-to-skin contact including kissing, fingering, mutual masturbation, rimming and fisting.
Using condoms during penetrative sex will help to reduce the risk of picking up or passing on syphilis.

If you’ve been diagnosed with syphilis and have received treatment, you can still pass syphilis on for at least 2 weeks after completion of that treatment. Avoiding sex for 2 weeks after treatment will prevent you from passing it on.

If you’re having lots of sex, regular syphilis testing means you can be treated for syphilis quickly if you have it. Getting treated quickly reduces the chance of passing it on to other people.

To find out more about syphilis prevention during pregnancy see here


Some people decide to reduce the risk of getting syphilis by taking an antibiotic called doxycycline on an on-going basis. This is called doxycycline prophylaxis or doxy PrEP (pre exposure). This involves taking 100mg of doxycycline every day.

Others decide to take doses of doxycycline soon after sex that might have exposed them to syphilis or other bacterial STIs. This is often referred to as doxy PEP (post exposure).

This same medicine is commonly used by travellers to prevent malaria infection. It is also used for treatment of other conditions such as acne. Side effects of this medicine include increased risk of sun burn and heart burn.

There is not currently agreement among doctors and researchers about the use of doxy PrEP and PEP - and many doctors will not prescribe doxycycline for these purposes. As a result, many people buy their doxycycline online.

There is some clinical and personal experience that taking doxy PrEP or PEP appears to prevent syphilis and some other bacterial STIs. There are a number of small studies underway to explore this further.
Some doctors and researchers are concerned that use of antibiotics in this way might contribute to antibiotic resistance. Others think that targeted use of doxy PrEP or PEP might be a way of preventing syphilis transmission. Current UK guidance from Public Health England and BASHH about doxy PEP can be read here.