Thank you for your question. Kissing is a least risky sexual activity. Herpes (HSV 1 & 2) is the only STI that is know to spread through kissing. Herpes is one of the most common infections but the stigma around it makes it difficult to speak about it. If you’re concerned about herpes and you think that you or your partner may have it, its best to have an honest discussion with your partner and discuss ways to prevent its spread.
One way to prevent is to be watchful and look out for symptoms that indicate that you are likely to have an outbreak such as burning and painful sensation, itching or tingling feeling in and around your mouth area. If any of these are appearing, it might be signs of herpes. It is recommended to avoid kissing if you or your partners have sores on the lips or mouth or if you have an active oral infection (such as a herpes outbreak).
Having a chat with your health care provider would help in taking medications that can reduce the chances of transmission and management of a herpes outbreak.
Very rarely kissing may result in transmission of HPV and syphilis provided either of the partners have a wart or a syphilis lesion on their mouth. Majority of the STIs can be easy treated and managed so the key is to get tested and seek treatment.