A fishy smell from your penis is almost always caused by bacteria breaking down sweat, skin oils, or trapped moisture in the groin area. In most cases, better hygiene solves it. But if the smell persists, comes with discharge, or shows up alongside redness or pain, an infection or other condition may be driving it.
The Most Common Cause: Smegma and Bacterial Buildup
The groin has a naturally higher pH than most of your skin, sitting between 6.1 and 7.4 compared to the 4 to 6 range elsewhere on your body. That higher pH creates a friendlier environment for bacteria and fungi. When sweat, dead skin cells, and body oils collect under the foreskin or in skin folds, bacteria feed on that material and produce compounds that smell distinctly fishy.
If you’re uncircumcised, this buildup (called smegma) accumulates in the space between the foreskin and the head of the penis. It’s a whitish, waxy substance, and when bacteria go to work on it, the odor can be strong. Even circumcised men can develop a similar smell if sweat and bacteria build up around the base of the head or in the crease where the shaft meets the scrotum.
Washing with harsh, alkaline soaps can actually make things worse. Alkaline soap raises the skin’s pH for several hours after use, and that pH spike accelerates the growth of odor-causing and potentially harmful bacteria. A gentle, fragrance-free cleanser or just warm water is enough. If you’re uncircumcised, gently retract the foreskin during bathing, clean underneath, and always slide the foreskin back into place afterward to avoid swelling.
Balanitis: When the Head Gets Inflamed
Balanitis is inflammation of the head of the penis, and a bad smell is one of its hallmark symptoms. It’s common in uncircumcised men and can be triggered by a yeast infection, a bacterial overgrowth, skin conditions like eczema or psoriasis, or even an allergic reaction to soap, latex, or spermicide. Diabetes also raises your risk because higher sugar levels in urine and skin secretions feed yeast and bacteria.
Along with the smell, you might notice redness, swelling, itching, soreness, or a discharge that can range from white and clumpy (pointing toward yeast) to yellowish or cloudy (suggesting bacteria). A healthcare provider can figure out the cause with a simple swab of the area and, if needed, blood or urine tests. Treatment depends on the culprit: antifungal creams for yeast, antibiotics for bacteria, or switching to gentler products if it’s an irritation issue.
Yeast Infections in Men
Male yeast infections are more common than most people realize. They cause pain, swelling, patchy redness in the groin, and sometimes a foul-smelling discharge. The smell from yeast alone tends to be more musty or bread-like than outright fishy, but when bacteria join the party alongside the yeast, the odor can shift toward that characteristic fish smell. Warmth, moisture, tight underwear, and a weakened immune system all set the stage.
STIs That Can Cause Odor
Certain sexually transmitted infections produce penile discharge that smells off. Trichomoniasis, gonorrhea, and chlamydia can all cause discharge from the penis, sometimes accompanied by burning during urination or irritation inside the urethra. In women, trichomoniasis is specifically linked to a fishy vaginal odor, and while the same organism infects men, the symptoms in men tend to be milder or even absent. Still, if you’re noticing a new smell alongside any discharge or burning, an STI is worth ruling out, especially if you’ve had a recent new sexual partner.
Urinary Tract Issues
Foul-smelling urine can sometimes be mistaken for a smell coming from the penis itself. Urinary tract infections in men are less common than in women but do happen, and they can make your urine smell strongly. Chronic prostatitis, an ongoing inflammation of the prostate, also lists foul-smelling urine among its symptoms, along with pelvic pain, difficulty urinating, and discomfort that comes and goes over weeks or months. If the fishy smell seems strongest when you urinate or you notice cloudy or unusually dark urine, the source may be urinary rather than skin-related.
A Rarer Possibility: Fish Odor Syndrome
Trimethylaminuria is a metabolic condition where your body can’t properly break down a chemical called trimethylamine, which is produced during digestion. The compound builds up and gets released through sweat, urine, and breath, giving off a strong fishy odor. Because the groin sweats more than most areas, you might notice it there first. This condition is genetic and persistent. If the smell affects your whole body (not just your groin) and doesn’t go away with hygiene changes, it’s worth mentioning to a doctor.
How to Fix It
Start with the basics. Wash daily with warm water and a mild, pH-neutral cleanser. If you’re uncircumcised, always clean under the foreskin. Dry the area thoroughly before getting dressed, since trapped moisture is the single biggest contributor to bacterial overgrowth. Switch to breathable cotton underwear and avoid sitting in sweaty clothes after exercise.
If the smell doesn’t resolve within a week of consistent hygiene improvement, or if you develop any of these alongside the odor, something more than simple buildup is going on:
- Discharge of any color from the tip of the penis
- Redness, swelling, or soreness on the head or foreskin
- Burning or pain during urination or ejaculation
- Sores, bumps, or rashes on the shaft or head
- Lumps in the groin area
These symptoms point toward an infection, an inflammatory condition, or, rarely, something more serious that needs a proper evaluation. Most causes of a fishy penile odor are straightforward to treat once identified.