A sewer-like smell from a shower often comes from a dry water seal, biofilm in the drain, or a venting or sealing problem. The first step is to separate surface odor from gas entering from the drainage system, especially in a rarely used bathroom.
Run water if the shower has not been used recently
The trap needs water to block sewer gases. Run water for about a minute and wait; if the smell disappears in a rarely used shower, evaporation of the water seal was a likely cause.
Clean hair and biofilm near the grate
Hair, soap, and organic residue can form an odorous film. Remove accessible debris and clean drain surfaces with a compatible product, never mixing bleach with acids, vinegar, ammonia, or other cleaners.
Odor that returns with gurgling can point to venting or pressure
If the odor appears when a toilet flushes or another fixture runs and comes with gurgling, pressure changes may be disturbing the trap seal. That calls for checking venting, blockages, or connections rather than just cleaning the grate.
Persistent odor with leaks or damaged seals needs repair
Check accessible areas for failed seals, loose drain fittings, or moisture beneath the shower. If there is structural dampness, sewage backup, or the odor persists with a full trap and clean drain, plumbing inspection is appropriate.
Sources
- U.S. Environmental Protection Agency (EPA) — WaterSense Home Maintenance — Household water maintenance, leaks, fixtures, and efficiency.