What Is the Bulbourethral Gland and What Does It Do?

The bulbourethral gland is a small, pea-sized gland in the male reproductive tract that produces pre-ejaculatory fluid, the clear, slippery secretion that appears at the tip of the penis during sexual arousal. Most people have heard of pre-ejaculatory fluid but have no idea where it comes from. The answer is this pair of glands, tucked deep in the pelvis, doing quiet but meaningful work: lubricating the urethra, neutralizing residual acidity from urine, and preparing the path for sperm. The gland is also called Cowper’s gland, a name that turns up more often in clinical settings and has its own interesting backstory.

Where It Sits and What It Looks Like

You have two bulbourethral glands, one on each side of the urethra, embedded in the muscles of the pelvic floor just below the prostate. Each gland is roughly the size of a pea, measuring about half a centimeter to a centimeter across. They sit within the urogenital diaphragm, the muscular layer between the base of the bladder and the perineum. Their ducts run forward and open into the bulbar urethra, the section of the urethra that passes through the base of the penis.

The glands are surrounded by a mix of muscle types. Research on the detailed anatomy has shown that striated (voluntary) muscle fibers wrap around the glands laterally, while smooth (involuntary) muscle sits along their inner aspect.¹ This dual-muscle arrangement matters because it means the gland’s secretion can be pushed out both by reflexive contractions you don’t consciously control and by voluntary contractions of the pelvic floor. The glands are small enough that they don’t show up on routine imaging unless something is wrong with them, which is part of why most people never learn they exist.

What It Produces and Why

The bulbourethral glands contribute roughly 0.1 to 0.2 milliliters to the overall ejaculate, a tiny fraction of the total volume.² But their real work happens before ejaculation. During sexual arousal, the glands release a clear, viscous, mucus-like fluid into the urethra. This pre-ejaculatory secretion serves several purposes:

Lubrication: The fluid coats the urethral lining, reducing friction for sperm that will travel through during ejaculation. It also provides some external lubrication at the tip of the penis.
Neutralization: Urine is acidic, and traces of it linger in the urethra between urinations. Sperm are sensitive to acid, so the alkaline pre-ejaculatory fluid helps neutralize that residual acidity, creating a more hospitable environment for sperm survival.
Cohesion of semen: The glycoproteins in the secretion contribute to the gel-like consistency of semen, helping it coalesce rather than scatter.

The secretion itself is rich in mucins and glycoproteins, the same class of molecules that make saliva and other bodily mucus slippery. The gland’s activity ramps up during arousal and can produce noticeable amounts of pre-ejaculatory fluid well before orgasm, which is why the fluid is sometimes colloquially called “pre-cum.”

How the Gland Knows When to Secrete

The timing of bulbourethral secretion isn’t random. The glands are wired into the nervous system through two separate pathways. The autonomic nervous system, the branch that handles involuntary functions like heart rate and digestion, supplies one set of signals. This autonomic input comes through the cavernous nerve, the same nerve bundle involved in erections. But research in animal models has shown that there’s also a somatic (voluntary) nerve contribution to the gland’s secretion, which operates alongside the autonomic pathway.³

This dual innervation helps explain something anyone with a penis has noticed: pre-ejaculatory fluid can appear during sustained arousal without any physical stimulation (autonomic drive), but it can also seem to increase with certain physical contractions (somatic drive). The cooperation between these two nerve pathways, combined with the mixed striated-and-smooth muscle architecture around the gland, creates a secretion mechanism that is partly reflexive and partly responsive to physical engagement.

Can Pre-Ejaculatory Fluid Cause Pregnancy?

This is probably the most practical question people have about the bulbourethral gland, even if they don’t know the gland by name. The short answer is yes, it can, though the mechanism is more nuanced than most sex-ed classes suggest.

The bulbourethral glands themselves do not produce sperm. Sperm are made in the testes and travel through the vas deferens, mixing with fluids from the seminal vesicles and prostate along the way. Pre-ejaculatory fluid originates from a completely different source. However, a study examining pre-ejaculatory samples from 27 men found that about 41% of them had sperm in their pre-ejaculatory fluid, and in most of those samples a substantial portion of the sperm were motile, meaning alive and swimming.⁴

Where do those sperm come from? The leading explanation is that sperm left over from a previous ejaculation can linger in the urethra or the ejaculatory ducts and get flushed forward when the bulbourethral glands push pre-ejaculatory fluid through. One striking finding from that study was that the pattern was consistent within individuals: men who had sperm in one pre-ejaculatory sample had them in every sample they provided, and men who didn’t have sperm never did across multiple collections.⁴ This suggests the issue isn’t just about recent ejaculation history. Some men may have anatomical differences that make it easier for sperm to leak into the urethral pathway before ejaculation.

The takeaway for contraception is straightforward: the withdrawal method is unreliable in part because of this gland’s fluid. Even if the man withdraws before ejaculation, pre-ejaculatory fluid carrying viable sperm may have already been deposited.

Pre-Ejaculatory Fluid and Sexually Transmitted Infections

Beyond pregnancy, pre-ejaculatory fluid raises questions about disease transmission, particularly HIV. Because the fluid passes through the urethra and can pick up cells and pathogens along the way, it has long been considered a potential route for spreading sexually transmitted infections during unprotected sex, even without ejaculation.

Research on this question has produced a reassuring finding for people on effective HIV treatment. A study of 52 men with HIV who were on suppressive antiretroviral therapy and had undetectable virus in their blood found that none had detectable HIV in their pre-ejaculatory fluid. Interestingly, about one in five of those same men did still have detectable HIV in their semen, suggesting that the seminal vesicles and prostate can harbor the virus even when blood levels are undetectable.⁵ The researchers concluded that pre-ejaculatory fluid may not contribute to HIV transmission in men on effective therapy, at least in the absence of genital infections.

That said, this finding applies specifically to people with well-suppressed viral loads. For people not on treatment, or with other STIs like gonorrhea or chlamydia that can infect the urethra itself, pre-ejaculatory fluid remains a plausible route of transmission. Delaying condom use until just before ejaculation is considered a risk factor for STI transmission in part because of exposure to pre-ejaculatory fluid during the unprotected interval.⁵

Things That Go Wrong With the Bulbourethral Gland

Because the glands are small and tucked away, problems with them are uncommon. But when they do occur, the symptoms can be surprisingly disruptive and tricky to diagnose, partly because many clinicians don’t think to look at these glands.

Syringocele

The most well-documented disorder is a syringocele, a cystic dilation of the bulbourethral gland’s duct. Think of it as the duct swelling up like a small balloon where it connects to the urethra. Syringoceles come in two forms: closed, where the cyst bulges into the urethral wall without an opening, and open, where there’s a connection that allows urine to flow backward into the dilated duct. In adults, the main symptoms are persistent dribbling after urination, urinary frequency, urethral pain, blood in the urine, or an unexpected urethral discharge. A study of seven adult patients with the condition found that those treated with a minor endoscopic procedure were completely symptom-free afterward, with follow-up averaging about a year.⁶

In children, syringoceles can present differently. Older boys tend to show up with difficulty urinating or blood in the urine, while infants more often develop urinary tract infections with fever.⁷ The condition is considered rare, and its rarity is part of the problem. Because it’s uncommon, it can be misdiagnosed as a stricture or another urethral issue, leading to delayed treatment.

Cowperitis

Cowperitis is inflammation of the gland itself, which can be acute or chronic. Acute cases cause fever, perineal pain (deep pain between the scrotum and anus), urinary urgency, and sometimes difficulty defecating or urinary retention.² In rare cases, the infection can progress to an abscess that requires drainage or even lead to sepsis. Recurrent cowperitis often signals an underlying structural problem like a syringocele or a fistula connecting the gland to the skin near the anus.⁸

Other Rare Conditions

Stones can form within the bulbourethral gland or its duct, similar to how stones form in the salivary glands or kidneys. These are typically visible on imaging as small calcified densities near the bulbar urethra.⁸ Cancer of the bulbourethral gland is exceedingly rare. As of 2016, only nine cases of Cowper gland adenocarcinoma had been reported in the medical literature.⁹ Given how few cases exist, there’s no standardized screening or treatment protocol. When the gland does show up on prostate MRI, it can sometimes be mistaken for prostate cancer or a prostate nodule, which is a diagnostic pitfall radiologists have to be aware of. In one series, benign Cowper’s gland tissue appeared as encapsulated masses up to 3 centimeters on MRI, and targeted biopsy confirmed there was nothing malignant.¹⁰

The Female Equivalent

Women have a homologous structure called the Bartholin’s gland (also known as the greater vestibular gland), located on each side of the vaginal opening. Bartholin’s glands and bulbourethral glands develop from the same embryonic tissue and serve analogous purposes: both produce lubricating mucus in response to sexual arousal.¹¹ Bartholin’s glands are better known clinically because their cysts and abscesses are relatively common, affecting roughly two to three percent of women at some point. The bulbourethral gland’s male equivalent of these cyst problems exists but is diagnosed far less often, likely because the gland’s deep location makes it harder to examine directly.

How the Gland Changes With Age

The bulbourethral gland isn’t static over a lifetime. Research tracking the gland’s cellular activity across age groups has found a dynamic pattern. During infancy and early childhood, there’s a burst of immune-cell activity and cell proliferation within the gland. This settles down during late childhood and early adolescence, reaching a low point in late adolescence and early adulthood, the period when the gland is presumably functioning at its peak for reproductive purposes. Then, starting in middle adulthood (the mid-thirties to forties), proliferative activity and immune-cell presence begin climbing again, a pattern that continues into old age.¹²

What this means practically is still being worked out. The increase in immune cells and proliferative activity in older men could reflect low-grade chronic inflammation, a pattern seen in many glandular tissues as people age. It might also explain why older men sometimes report changes in the amount or consistency of pre-ejaculatory fluid, though there isn’t robust clinical data linking these cellular changes to noticeable symptoms. The strong correlation between immune-cell numbers and proliferative activity in the gland tissues suggests the two processes are linked, possibly as part of the gland’s ongoing tissue-maintenance response.¹²

How the Gland Got Its Name

The gland is almost universally called Cowper’s gland in clinical practice, after the English anatomist William Cowper, who published a detailed description of its structure, location, and function in 1699. But the gland had been spotted before him. The first known illustration appeared in 1600 in a set of anatomical plates by the Italian anatomist Hieronymus Fabricius of Acquapendente. And in 1684, a French surgeon named Jean Méry described the glands in a published account, predating Cowper by fifteen years.¹³ There was some historical controversy over priority, the kind of academic naming dispute that was common in early anatomy. Cowper’s name stuck largely because his description was the most thorough and widely circulated. The more neutral term “bulbourethral gland,” which simply describes the gland’s location near the bulb of the urethra, has been gaining ground in modern anatomy textbooks precisely to sidestep these attribution debates.

When the Gland Mimics Other Problems on Imaging

With prostate MRI becoming more common for cancer screening, radiologists are increasingly encountering the bulbourethral gland in scans where it wasn’t the focus. A normal bulbourethral gland is small enough to be unremarkable, but benign enlargement (hyperplasia) can produce a mass that sits right next to the prostate and looks suspicious. In one multi-center imaging review, enlarged Cowper’s glands appeared as encapsulated masses with signal characteristics that could easily be confused with a prostate cancer nodule extending beyond the gland.¹⁰ Similarly, hemorrhagic cysts of the gland can be picked up incidentally on prostate MRI and require follow-up imaging to rule out a tumor.⁸

For the average person, the practical implication is this: if a prostate MRI report mentions a finding near the “urogenital diaphragm” or “bulbar urethra,” it may relate to the bulbourethral gland rather than the prostate itself. Awareness of this gland’s existence and its position right next to the prostate can save patients unnecessary anxiety and, in some cases, unnecessary biopsies.

1
Scientific Reports. Anatomy of Cowper’s gland in humans suggesting a secretion and emission mechanism facilitated by cooperation of striated and smooth muscles
2
PubMed Central. Sepsis secondary to Cowper’s gland abscess
3
PubMed. Somatic innervation contributes to the release of bulbourethral gland secretion in male rats
4
PubMed Central. Sperm content of pre-ejaculatory fluid
5
PubMed Central. HIV-1 is undetectable in pre-ejaculatory secretions from HIV-1-infected men on suppressive HAART
6
PubMed. Cowper’s syringocele: symptoms, classification and treatment of an unappreciated problem
7
PubMed. Cowper’s syringocele: A rare differential diagnosis of infravesical obstruction in boys and young adults
8
PubMed. Imaging of the Bulbourethral (Cowper) Gland: Abnormalities and Differential Diagnosis
9
PubMed Central. Cowper gland adenocarcinoma
10
PubMed Central. Cowper’s gland hyperplasia: A potential pitfall at MRI of the prostate
11
Mathews Journal of Gynecology & Obstetrics. Bartholin’s Gland is an Important Part of the Female Reproductive System
12
Heliyon. Age-related dynamics of T cells and epithelial proliferative activity in human bulbourethral glands
13
PubMed. The history of discovery of bulbourethral glands