Brief Answer:
Risk is low but not Zero

Detailed Answer:
Hello. Thank you for writing to us

I am Dr. Kakkar (MD, Dermatology and STDs). I have read your query and I have understood your concern.

Performing unprotected oral sex on a female though believed to have a very low risk of acquiring an STD's is not considered to be entirely safe. Almost all the STDs can transmit through oral sex including herpes, syphilis, gonorrhea, chlamydia and even HIV.
Herpes virus commonly gets passed on through this route however the likelihood depends on the presence or absence of genital sores. Presence of genital sores makes transmission more likely.
Similarly, it is possible to acquire throat gonorrhea and chlamydia, performing oral sex on a female, if the partner had genital infection with these organisms.
Syphilis can have genital lesions in its course, specially during secondary stage of syphilis which are teeming with Treponemes, therefore theoretically if someone has genital mucous lesions of syphilis he/she can pass it on through oral sex.
Hiv is a risk since there is a direct oral to genital mucosal contact and infectious secretions can pass through. Though the risk is lower than vaginal or anal sex.
Therefore i would suggest that you get yourself screened with with full panel of STD tests at appropriate intervals to exclude whatever little risk that is associated with Oral sex.
There are no exact figures for risks involved from a purely oral sexual encounter, because most individuals who have oral sex also practice other forms of sex during the same sexual encounter.

Regards

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