Get this: it is completely possible to get STDs through oral sex. While the contraction of STDs mostly occurs via vaginal or anal sex, oral sex is not magically excluded as a way through which it can spread, too. STDs like HPV, gonorrhoea, syphilis, herpes, and Hepatitis B can all be spread through oral sex, so play it safe with a condom. Tip: That’s what the flavoured variants are for.

Reference: http://www.mayoclinic.org/std-symptoms/art-20047081