What do urology and gynecology studies say about the composition of expelled fluids?
Executive summary
Urology and gynecology literature describe multiple distinct expelled fluids during sexual activity — including urine from the bladder, fluids identified as “female ejaculation,” and vaginal or uterine secretions — and emphasize that composition and origin vary by mechanism and individual anatomy [1] [2]. Multiple objective studies and reviews conclude that many large-volume “squirting” events are chemically indistinguishable from urine or are urine altered during arousal, while smaller-volume, milky or mucous emissions sometimes labeled female ejaculation have been documented as distinct but are far less consistently characterized in the literature [3] [4] [2].
1. Anatomy and baseline chemistry: what the urinary and reproductive systems normally expel
The urinary tract is the body’s drainage system: kidneys filter blood and produce urine, which is transported to and stored in the bladder before being expelled via the urethra; urine composition varies with hydration, hormones, medicines and kidney function [5] [6]. Reproductive tract secretions — vaginal transudate, cervical mucus and uterine fluid — have different origins and biochemical roles; recent work characterizes uterine fluids collected under sterile conditions for fertility research, underscoring that reproductive fluids are collected and analyzed by gynecologists as distinct biological fluids [7].
2. The clinical problem: multiple fluids, multiple labels, one confusing literature
Reviews and systematic analyses across decades stress that reported “expelled fluids” during sexual activity are not a single phenomenon; they encompass coital incontinence (leakage of urine during intercourse), squirting (often high-volume expulsions), and what some call female ejaculation (typically lower-volume, milky secretions), and confusing terminology has long muddled comparisons between studies [1] [2] [8].
3. Objective studies: catheterized women and the bladder as a frequent source
Classic experimental work catheterized small cohorts of women who reported regular expulsions and found that, even after bladder drainage, participants expelled volumes into collection bags and that the primary conclusion in several experiments was that most expelled fluid originated from the bladder — suggesting urine as the source for many events described as squirting [3] [4].
4. Chemical analyses: urine, altered urine, and possible distinct secretions
Narrative reviews and laboratory analyses report that many expelled fluids contain chemical markers consistent with urine, leading investigators to infer that some expulsions are urine or “altered” urine produced by physiological changes during arousal; at the same time, on occasion teams observed milky, mucous-like emissions that may differ in composition and origin from simple urine, though these observations are limited in number [4] [3] [1].
5. Prevalence and volume: wide ranges, weak survey data, and objective case counts
Questionnaire-based studies have reported highly variable prevalence estimates for fluid expulsion during sexual activity (reports cited in reviews range roughly from about 10% to over 50%), but systematic reviewers caution these figures are unreliable because objective evidence is limited; measured volumes reported in the literature vary drastically, from fractions of a milliliter up to nearly a liter in extreme cases, further supporting heterogeneity in origin and mechanism [8] [2].
6. Diagnostic approach and the limits of current knowledge
Authors of narrative and systematic reviews urge differential diagnostic approaches — distinguishing coital incontinence, bladder-origin squirting, and true female ejaculation — and highlight small sample sizes, inconsistent collection methods, and possible observer bias as barriers to firm conclusions; where laboratory collection was rigorous, bladder-origin findings predominate, but the literature leaves room for rare non-urinary secretions and for biochemical modification of urine during arousal [1] [2] [4].
7. Bottom line for clinicians and researchers
Current urology and gynecology studies collectively indicate expelled fluids during sexual activity are heterogeneous: a substantial portion are urinary in origin or urine-like (often termed squirting), some expulsions present as distinct milky or mucous secretions that could be non-urinary but are less well documented, and rigorous biochemical differentiation requires careful sampling methods that many older studies lacked [3] [4] [2]. The literature therefore supports cautious interpretation, recommends standardized sampling and biochemical assays, and acknowledges remaining uncertainty about the frequency and precise composition of non-urinary “ejaculatory” fluids [1] [8].