Female ejaculation (or squirting) is caused by stimulating the g-spot. Since the g-spot is the internal part of a woman's clitoris that wraps around her urethra and creates a sponge-y texture on the vaginal walls, the secretions, or ejaculate, it creates build up in her urethra. Upon orgasm (a series of involuntary muscular contractions), the ejaculate either is sucked up into the bladder or pushed out of the urethra. If it is pushed out, it can either gush (like what you see in porn) or seep (that wet spot on the bed). Since it's a bodily fluid, there is a possibility of STI transmission through ejaculate. Unfortunately, not many studies have been done regarding the rate of transmission between women (or men who go down on women) or which STIs are more likely to pass through this type of play.

In all honesty, if you're going down on her without a dam, you're already exposing yourself to a provider's bodily fluids. Just remember that when you go to the doctor for your regular testing (because of HIPAA, it's actually illegal for the doctor to share any information about your testing or its frequency with your spouse or partner unless you state otherwise), you want to get an oral culture as well. This way, you're testing for bacterial nasties like Chlamydia and Gonorrhea in both your mouth and throat as well as your junk.

That being said, I'm new to the area and don't know any regular squirters here yet (I can do it, but I'm not consistent. It happens maybe about 5% of the time.). I'm sure that someone will read this and point you in the right provider's direction. Hopefully this was helpful and good luck!