TL;DR
A restroom that smells despite being cleaned properly has a source, and adding fragrance never fixes it. The three most common causes are a dry floor drain trap letting sewer gas into the room, urine saturated into porous grout and floor base, and buildup inside urinal or fixture drain lines. Each has a different fix, and none of them are a cleaning frequency problem.
Start by ruling out cleaning
Before hunting a hidden source, confirm the basics are happening, because a genuinely under-cleaned restroom smells for obvious reasons.
The tells are visible: soil at the base of fixtures and in the grout around them, a film on the floor near the urinals, waste containers not emptied, standing water. If any are present, the answer is the cleaning program rather than a plumbing mystery -- start with how commercial restrooms are cleaned. But if the room is visibly clean and still smells, the source is somewhere cleaning does not reach.
Why does a clean commercial bathroom still smell?
Usually because urine has soaked into porous surfaces such as grout and the floor base where surface cleaning cannot reach it, because a floor drain trap has dried out and is admitting sewer gas, or because buildup has formed inside a urinal or fixture drain line. All three persist through normal cleaning.
Source one: the dry floor drain trap
This is the most commonly missed cause and one of the easiest to fix.
Floor drains have a U-shaped trap holding a small amount of water, and that water is the seal keeping sewer gas out of the room. In a rarely used drain -- which describes most restroom floor drains -- the water evaporates over weeks, the seal breaks, and gas comes up.
The signature is distinctive: the smell is worst near the floor, strongest after a quiet period such as a long weekend, and often improves briefly after mopping because mop water temporarily refills the trap.
The fix is to pour water into each floor drain on a schedule, which restores the seal. Some buildings add a small amount of mineral oil on top to slow evaporation, and some install trap seal devices where drains are chronically dry. If water does not resolve it, the problem belongs with a plumber.
Source: Building plumbing maintenance practice
Source two: saturated grout and floor base
Urine that reaches the floor does not stay on the surface. It travels into grout lines, into the joint where the floor meets the wall base, and into any porous flooring material.
Once it is in there, surface cleaning stops helping. The odor releases continuously and gets worse in warm, humid conditions, which is why a restroom that seems tolerable in winter becomes unbearable in summer.
The signature: the smell is strongest at the floor near urinals and toilet bases, worse in warm weather, never fully gone after cleaning, and the grout there looks darker than elsewhere.
The remedies escalate. Deep grout cleaning removes what is reachable, an enzyme treatment breaks down residue that ordinary cleaners do not, and sealing afterward prevents a repeat, since unsealed grout simply re-absorbs -- see whether sealing grout actually helps. One caution: never use an acidic product on natural stone floors or bases, because acids permanently etch marble, travertine, and limestone.
Source three: urinal and fixture drain lines
Buildup inside a drain line produces odor from within the fixture rather than from the room.
The signature: the smell comes from a specific fixture and is much stronger with your head near it, and the fixture may drain slowly. Deposits can accumulate inside the trap and line over time and hold odor.
Fixture-specific care depends on the unit, and the manufacturer's guidance governs -- particularly for waterless or low-flow urinals, which have their own cartridge or sealant systems and are damaged by the wrong approach. Persistent slow drainage is a plumbing problem, not a cleaning one.
Source four: the things people forget to check
A handful of less common sources account for most of the remaining cases.
Behind and under fixtures. The gap behind a toilet base and the underside of a urinal are rarely cleaned properly.
Partition bases and hardware. Partition panel bottoms and floor mounts sit in the splash zone, as do wall surfaces near urinals.
Waste containers themselves. A bin with residue in the body from a leaked liner smells regardless of how often it is emptied.
Mop equipment. A mop head or bucket stored wet in the restroom closet goes sour and re-spreads odor every service.
Exhaust that is not working. A failed or blocked exhaust fan lets humidity and odor accumulate. Easy to check, and frequently the culprit when a room worsens suddenly.
Why air fresheners make diagnosis harder
Fragrance does not remove odor. It sits alongside it, and the combination is usually more unpleasant than the original.
More importantly, masking removes the signal. A room that smells tells you where and when, which is diagnostic information. Dispensed fragrance has a place once a source has been eliminated and the room is genuinely clean. Using it as the primary response is how a small problem becomes a saturated floor.
Working the diagnosis
A short structured check usually finds it. Visit the room first thing in the morning, before service, after the building has been closed overnight -- that is when a dry trap and a saturated floor are both at their worst and easiest to distinguish.
Then get low. Most restroom odor sources are at or below knee height, and standing at the door tells you very little. Check near each floor drain, near the base of each urinal and toilet, at the wall base, and inside each waste container. Note where it is strongest and when it is worst, then match that against the signatures above. Once you have a candidate, the fix is usually straightforward, and if it turns out to be plumbing or exhaust, the report needs to go to whoever handles building maintenance rather than the cleaning contractor -- see working with a building manager.
If the cause turns out to be program rather than plumbing, the structure of a proper service and round schedule is in restroom service rounds and restocking.
FAQ
Why does my commercial bathroom smell even after cleaning?
Usually because the source is somewhere cleaning does not reach: a dry floor drain trap admitting sewer gas, urine soaked into porous grout and floor base, or buildup inside a fixture drain line.
What causes a sewer smell in a commercial restroom?
Most often a floor drain whose trap has dried out. The water in the trap is the seal blocking sewer gas, and in a rarely used drain it evaporates over weeks. Pouring water into each floor drain periodically restores the seal.
How do I get urine smell out of restroom grout?
Deep clean the grout, treat the area with an enzyme product designed to break down residue, then seal the grout so it stops re-absorbing. Never use acidic products on natural stone floors or bases.
Do air fresheners fix restroom odor?
No. Fragrance sits alongside odor rather than removing it, and the combination is usually worse. It also removes the diagnostic signal you need to find the source.
Why is the restroom smell worse on Monday mornings?
That pattern points to a dry floor drain trap. During a quiet weekend no water enters the drain, the trap seal evaporates, and sewer gas builds up in the room. The smell often improves briefly after the floor is mopped.
Should odor problems go to the cleaner or to building maintenance?
If the room is visibly soiled, it is a cleaning issue. If it is visibly clean and still smells, the likely causes are plumbing, grout saturation, or a failed exhaust fan, all of which belong with building maintenance.
Odor that survives a good cleaning program is a diagnosis problem rather than a frequency problem, and it usually takes a look at the actual room. Get a quote and we will help you work through it, or read more about commercial cleaning services.