Yo steveo!
Google is your friend, as they say, and the big bad guv'ment and other do-gooders have loads of info on STIs out there, for example:
http://www.healthdirect.gov.au/sexually-transmitted-infections-sti and
http://www.sti.health.gov.au/internet/sti/publishing.nsf/Content/key-information-faqs. This tells you:
What does safe sex actually mean?
Safe sex is when you don’t exchange semen, vaginal fluids or blood with your partner. This reduces the risk of getting or passing on STI and unplanned pregnancy. While the only way to be 100 per cent safe is to avoid sex altogether, you can improve your safety. You can make the choice to always use a condom if you’re having sexual intercourse; have you and your partner tested for STI regularly and try not to have multiple partners.
You can also try safer sexual activities that don’t involve actual intercourse, such as kissing, massage, oral sex with a condom and mutual masturbation.
(So this suggests kissing and CBJ are
relatively safer than vaginal intercourse -- no surprises there.)
If I only have oral sex, can I get an STI?
Unprotected oral sex can spread some STI, particularly herpes. Bacterial infections like gonorrhoea and syphilis can also be spread through oral sex.
If you have oral sex you should still use condoms and avoid getting semen or blood in your mouth or on any area of broken skin.
(This points out that you can catch various nasty bugs through BBBJs, so CBJs are much safer.)
Now 'kissing' on these sites is not defined (is it only light kissing or DFK also?) and is portrayed as quite safe, but I'm pretty sure there is a (perhaps comparatively small) risk of catching HSV (1 especially, 2 more rarely) and HPV from exchange of saliva that occurs with DFK. But they may not classify HSV-1 (the cold sore virus) as an STI these days because it is so common in the population and can be caught through non-sexual contact as well. Similarly with many types of HPV which can cause different kinds of warts, not just on the genitals.
As it advises above, 'the only way to be 100 per cent safe is to avoid sex altogether'. But who wants to be Bubble Boy all their life? Sensible precautions like condoms can minimise (not eliminate) the risk, while still allowing all of us a high degree of mutual pleasure.
Stay safe, dude!
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