Hello dear, Thank you for your contact to health care magic. I read and understand your concern. I am Dr Arun Tank answering your concern. No, if both of you don t have any STDs than it will never cause any STDs to any body. Anal openings are very narrow and can not allow the penis to enter into the hole. As if you are doing sex by this way it causes friction and injury to the mucosa of the analcanal anf causes burning. It is not a STDs but because of injury STDs can occur at the injured part. I advice you not to do anal sex as it is against the nature. If you want to do than you can do with proper precautions like applying anaesthetic jelly and muscle relaxant with condon applied. Oral sex is safe as it is large opening you can do it. I will be happy to answer your further concern on bit.ly/DrArun. Thank you, Dr Arun Tank Infectious diseases specialist, HCM.