I sat on a wet chair in a restaurant. is it possible to get syphilis from sitting on a wet seat? (wet substance unknown).

No: This would be very unlikely to happen.

You sound anxious.: This would be a highly unlikely scenario for transmission of syphilis. Syphilis is spread when broken skin or mucus membranes come in contact with sores that contain the bacteria. Sores can be found in the vagina, anus, rectum ; external genitalia. There can be sores on the lips ; mouth. Infrequently kissing can lead to infection when there is contact with a sore. This std can be spread during.

Why do you ask?: No. Syphilis is caught from direct contact to the primary lesion known as a chancre, or semen or blood direct to your skin. Some people can or have been known to get syphilis from saliva when there is a primary lesion in the mouth of an infected human. But, sitting any any fluid will not give you any std, let alone syphilis.