Yesterday I met a guy of 24 years old and we chatted a bit. Since I was VERY cautious these days about sexual safety... we didn't do any penetration nor oral job. But we hugged each other and I performed annilingus to him for about 1-2 minutes. Before the activity, I carefully asked him about his status, and he told me he was all negative. Then I carefully checked his anal area- nothing abnormal and it was very clean, at least the area I could see with my eyes. I even took a photo of it. My question is, should I be concerned about syphilis if there was no visible lesion on his anus? Could a lesion like chancre inside his anus and I licked it with my tongue tip? Thanks for your help.