When aroused, some women may experience squirting, or a rather noticeable discharge of fluid. What it is exactly and where it comes from has been hotly debated: female ejaculation or adult bedwetting? Researchers are now saying that squirting is essentially involuntary urination.

Female ejaculate is technically the small amount of milky white fluid that’s expressed when climaxing, New Scientist explains. Squirting, on the other hand, results in a much larger gush of a clear fluid, which comes from the urethra, the duct where urine is conveyed from the bladder. The findings, which combine biochemical analyses with pelvic ultrasounds, were published in the Journal of Sexual Medicine on Christmas Eve.

A French team led by Samuel Salama from Hopital Privé de Parly II recruited seven healthy women—who’ve reported recurrent and massive fluid emission (enough to fill a cup) during sexual stimulation—to undergo “provoked sexual arousal.” The team conducted pelvic ultrasound scans after urination and during sexual excitation just before and after the squirting event.

All of the women had empty bladders before sexual excitation, however, urine collected just before squirting showed that the bladder was filling up. Urine sampled after squirting revealed that the bladder had been emptied again, revealing the origin of the squirted liquid.

The researchers also analyzed chemical concentrations in the urine samples (before arousal and after squirting) as well as the squirting sample itself. These included urea, uric acid, creatinine (a byproduct of muscle metabolism), and prostatic-specific antigen (PSA). The latter is a protein that’s produced in men’s prostate glands and in the “female prostate” called the Skene glands; PSA is found in “true” female ejaculate. Urea, uric acid, and creatinine concentrations were comparable in all of the urine and squirt samples. However, PSA, which was not detected before sexual simulation in six of the women’s urine samples, were present in urine collected after squirting and in the squirt sample in five of the women.

Squirting, they found, is essentially the involuntary emission of urine during sexual activity—though there’s also a small contribution of prostatic secretions as well. Salama’s team is now working on a protocol to test whether the kidneys work faster to produce urine during sexual stimulation than at other times, New Scientist explains. And if so, why.