I have to counter Justin's stat's here. As a monger who's barebacked a lot of women in the last 20 + years of being a manwhore/monger, I get tested frequently and I've been very lucky to not catch anything. The hardest one to get in hetero male to female sex is HIV, especially for the giver. However, it only takes one which is why once PreP became free, I immediately opted for the prescription. The quarterly tests are but a minor inconvenience, but I lose wood whenever using cover.
In the instance of STI's, the most common in the US are Gonorrhea, Syphilis, Chlamydia, and Herpes. All four of these can be asymptomatic, and extremely easy to catch, whether you use a condom or not, that's why you can catch these in other places around your genital areas. The tests for the first three kinda suck since they require oral and rectal swabs which are not comfortable. The good news is they now have DoxyPep available which if taken after sex it will drastically reduce the chance of getting it.
The hard one and often stigmatic one is Herpes. There are four types of herpes that affect humans: chicken pox, shingles, HSV-1, and HSV-2, so if you've ever had any of these you may test positive for the antibodies, however, tests for HSV-1 and 2 are unreliable, particularly blood tests. I asked my physician why none of my STI panels ever included HSV-2, much less 1. He gave me a bunch of pamphlets which was basically a summary of CDC, WHO, and peer reviews that estimate 10-20% of the world population has HSV-2; the one most commonly known as genital herpes. It goes on to say HSV-1, the more common of the two is suspected that 50% of those between the ages of 18-55 are infected, and up to 80% in the US.
Needless to say I was pretty freaked out about this and insisted upon a test, but he said the only reliable test for either HSV-1 and 2 is with a genital/oral swab, but in order to do that I would need to have the symptoms, primarily the blisters or cold sores (for the mouth). Another stat says most people who have HSV-1 get it before they're 5, mainly because of relatives kissing them - I actually Googled this to confirm. The reason I mention HSV-1 is because it's even easier to get than HSV-2, but it is now been discovered that, while it's not technically an STI, HSV-1 can be passed from the mouth of someone with an active sore that gives you a BBBJ. HSV-2 can be passed through oral sex as well, but not as common. So it is now a misnomer to call HSV-1 exclusively an oral STD as they've found HSV-1 on genitals, but HSV-2 is known to be worse.
The important part to consider so that those of us who have BB'd women is that over 3/4 of those who have either HSV-1 or 2 are asymptomatic. So, based on the statistics alone, a large percentage of us have either HSV, whether through kissing, or through sex. We just never experienced the commonly known symptoms of painful sores, and pus. If you think using a condom protects us, think again. If any fluid from a sore touches any part of your genital skin or mouth, like when you make a girl cum, you've been exposed - hence why you can get it on your inner thighs and your rectum. Oh, and you can also get both on other parts of your body, including your eyes.
Now, I am neither a medical doctor or a medical professional - just passing on knowledge provided by my PCP, and also with discussions with family and friends who are in the medical field. Whether you wish to continue or start BBFS/BBBJ is up to two consenting adults. Is it possible to catch something - YES. Are most of them curable or at least treatable? Absolutely. But, whether you use a condom or not, you can catch any of them. Best thing to do is get tested at least every 3-6 months. I recommend going to your PCP since the results tend to come faster than having to wait nervously for 2-3 weeks for a clinic/planned parenthood. I also recommend PreP and DoxyPep whether you plan on using protection or not.
TL
R - You can catch an STI whether you use cover or not. Gonorrhea, Chlamydia, Syphilis and Herpes are the most common, and are often asymptomatic. The only way to guarantee to be STI free is to be celibate. Spend the time to Google it if you don't believe me. I wouldn't blame you as I didn't believe it either.
