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Safe(sic) sex, also known as safer sex, involves methods beyond latex or other barriers. One simple one is using lots of lube. Simply put if one's cunt, cock or anus is abraded, transmission risk is increased.

HIV is on many people's minds because of it's fatal reputation (and the fact that while no longer uniformly fatal the available cocktails are hard on the body). However HPV, herpes, more strains of hepatitis than are technically classified, chlamydia, syphilis, Gonorrhea are all more transmissible and carry their own problems.

At this time (2002) with the availability of AZT and other treatments many people have declared that we have entered the post AIDS era. And not surprisingly, HIV infection rates which have been decreasing steadily for a decade are now slightly rising.

Other (than barriers) ways to practice safer sex:

Use lube (sexual lubricants), be sure they are latex (or barrier) compatible
Get educated; knowledge is power
If you are likely to bareback when you drink, be sober for sex
      Corollary don't be in denial, be able to be consciously sexual
Be conscious of the risks you do take, no method is risk free
If you're not monogamous, make informed choices about fluid bonding
Get tested often; see that your partners do also

Some (approximate) facts

Latex disintegrates in the presence of nearly all lipids (oils/fats)
HIV transmission in giving head is rare but it is not a zero risk
      If you have cuts in mouth or throat, herpes, bleeding gums etc risk is increased.
Anal sex is high risk for heterosexual or homosexual encounters

Unfortunately you have to do some math to evaluate risk, however if you never learn the odds the chances that you'll know what's relatively safe and dangerous and be able to act on that knowlege approach zero.

In part because more people are becoming more open about interesting sexual expression (no, anal play does not mean that you're gay), the exposures to STDs are increasing. Personally I believe that being responsibly aware of more than just the fantasy makes for hotter sex, with lower risk than if we were to limit ourselves to one roleset while denying the desire for something else.

That said, if het or vanilla or monogamous play is what works that's OK (and usually pretty hot) by me too.