Hello Cass, and thanks for writing to us.
Although there are less risk factors contracting STDs via oral sex, it is not entirely out of the question.
Most exchange of bodily fluids poses a health risk. Herpes is a disease which is easily transferable. Maybe more far-fetched but still possible, even deep kissing could produce some alarming effects, such as mouth sores and different strains of herpes. So imagine what can happen when placing mouth to genitals.
Also, the saliva from a person’s mouth, and lack of personal hygiene might produce some unsavory effects, such as candida yeast infections, or irritation and inflammation.
The best way to make sure you are not contracting any diseases or other unpleasantness, is to always use protection (dental dam, even made out of a condom sliced in half or a rubber glove if you have no condoms), and get tested for any STDs which may have been lingering from a previous partner. That goes for both partners, as women can give an STD or infection to a man by giving him oral sex too!
If you’d like to read a bit more about this, I suggest going to visit this URL: http://aids.about.com/cs/safesex/a/oralsex.htm
Be careful and I hope this sheds some light on the situation,