Everyone has different approaches to safe sex. There are those that tend to be overly responsible, and those who hope that they are lucky enough to be safe every time. The important thing to remember is that relationship is like a joined car ride. It’s more fun for the driver to drive fast, but then you not just endanger yourself, but your primary partner too, because you are in this together – they are in the car with you. I will write some common ways to protect yourself, but for more info, I’d suggest visiting the vast lands of the internet. I’ll be talking mostly about hierarchical relationships, but safe sex is anyone’s responsibility, and most info here is relevant enough.
If a man has unprotected sex with a secondary woman, she might get pregnant. Since it’s her decision whether to keep the baby, it’s his responsibility to be as safe as possible. This means that condoms or other contraceptives are required until he feels safe enough with her about her future decisions. Some couples have a rule to have redundancies – to have two birth control methods when having sex with secondaries – condoms and active use of birth control.
STIs – Sexually transmitted infections
There are different STIs – some are curable, some are only treatable with life-long treatment. You can get them from any sexual act including any penetrative sex, but also oral. The types of STIs for every type of sex, and the chances of getting them vary. Barrier contraceptives work best for most types of STIs including male and female condoms and [dental dams/flavored condoms/flavored lube with regular condoms] for oral. The discussion about fluid bondage (bare backing) is one to have with all the people involved (whether you are in a closed poly circle or not), while you should also check yourselves for STIs. In fact, it’s a common practice in non-monogamous relationships to have recurrent STI tests (usually every 6 months or a year). It’s also worth noting that every STI has its own incubation period (https://www.stdcheck.com/blog/how-soon-get-tested-for-stds-unprotected-sex/) so tests are only as valid as the time passed between last unprotected sex and the test. Although some curable infections have antibiotic-resistant counterparts, there is still very little chance of you getting it (but some don’t want to take that chance either). Treatable incurable infection are HIV, Hepatitis B, and Hepatitis C.
Additional resources about types of transmission and STIs in general: http://www.sfcityclinic.org/stdbasics/stdchart.asp
So what should we look for?
Essentially it depends on your comfort level. It’s obvious that penetrative sex is a dangerous activity when unprotected, without verifying the health status of your partner.
Other activities may include oral sex, “scissoring” (tribadism), sharing sex toys and drawing blood (kink community related – like impact play with a cane). Kissing, dry humping and other “second base” activities considered relatively safe. In every case, you should educate yourself which infections can be transferred, and what are the chances. This way you’ll be able to make an informed decision about your safety, and the safety of your partners.
Since incubation period of HIV is up to 3 months, I would suggest doing STI tests knowing the last 3 months of that person’s sexual history. Even if you don’t want to be fluid-bonded, condoms can slip. If you do want to be fluid bonded, it’s an essential step in acting responsibly towards your partners.