Note to readers: This post was updated on July 23, 2026 to tighten the troubleshooting steps and link to related drain, P-trap, and mold guides. We refreshed the details below so the advice reflects how we approach this work today.
A weird smell coming from the shower is one of those things you notice the second you walk in the bathroom — and it’s usually one of a handful of common causes, most of which are simple fixes. Here’s how to track down the source and clear it up.
Step One: Find the Source
Before troubleshooting, figure out whether the smell is coming specifically from the drain or filling the whole bathroom. A drain-specific smell points to something local — a clog, biofilm, or a dry trap. A smell that fills the whole room, especially something closer to sewage, can mean a venting issue or a bigger problem worth having a plumber check.
Cause 1: A Clogged Drain
Hair, soap scum, and general debris build up in shower drains over time and slow the water down, which lets odors linger instead of washing away. If the shower is draining slowly or standing water lingers around your feet, this is the likely culprit. A plunger clears minor clogs; for anything deeper, a drain snake will reach further into the line.
Cause 2: Biofilm Buildup
Biofilm is a thin, slimy layer of bacteria that forms inside drains that stay wet constantly — it’s the same thing you might notice in a hotel shower drain. It’s not the same as mold, though the two get confused often; shower mold is a fungus and needs different cleaning. Biofilm usually clears with a pour of equal parts vinegar and hot water down the drain, left to sit for a few minutes before flushing.
Cause 3: A Dirty or Dry P-Trap
Every drain has a P-trap — a curved section of pipe that holds water to block sewer gas from coming back up into the room. If it collects debris or dries out from infrequent use, that seal breaks down and you’ll smell sewage rather than mildew. Running water through the drain for a minute often resolves a dry trap; a clogged one may need to be cleaned out directly.
Cause 4: A Leaking Pipe
A musty smell (as opposed to sewage) paired with any dampness on walls or flooring near the shower can point to a hidden leak. Leaks left unaddressed lead to mold growth and, over time, real structural damage. This is the one cause on this list that isn’t a DIY fix — if you suspect a leak, it’s worth having a plumber take a look before it gets worse.
When to Call a Plumber
Simple fixes handle most shower odors. Call a professional if the smell returns quickly after cleaning, if you notice any dampness or staining around the shower or nearby walls, or if the smell resembles sewage rather than mildew. Western Rooter has served the San Gabriel Valley for over 30 years and can track down the source fast — see our full list of service areas or contact us to get it sorted.
