Most of the time: biofilm and hair
Hair, soap scum, skin oils, and conditioner coat the inside of a shower drain and the trap. Bacteria grow on that film and it smells musty or sour, even when the shower still drains fine. This is the most common cause, and it is a cleaning job.
How to clean it
- Remove the drain cover or stopper. Many unscrew or pop out.
- Pull out hair with a plastic drain snake or bent wire. Expect it to look bad.
- Scrub the inside of the drain opening and the cover with a brush and dish soap.
- Flush with hot tap water for a few minutes.
Step-by-step with photos: how to unclog a shower drain. Skip chemical drain cleaners; they do not remove biofilm well and they are hard on pipes.
If it smells like sewer, not mildew
- A shower that is rarely used: The trap water evaporated. Run water for a minute. If the smell goes away, that was it.
- Gurgling when the shower drains: Points to a venting problem pulling the trap dry.
- Smell plus slow drains elsewhere: Points to the main line, not the shower.
- A remodeled shower that smelled from day one: In rare cases a drain gets installed without a proper trap. A camera can confirm.
When to call
If a thorough cleaning does not fix it, or the smell is sewage rather than mildew, the problem is below the floor. More causes in why does my house smell like sewer.
How Do I Keep the Smell From Coming Back?
Put a hair catcher over the drain and empty it after every few showers. Once a week, lift the cover and wipe the opening with a brush. Flush the drain with hot tap water for a minute. If the shower sits unused for weeks, run it briefly each week so the trap stays full of water. Keep conditioner and body oils from piling up by rinsing the floor of the shower as well as yourself. Bathroom fans help too, since damp air keeps the film growing.
Do Baking Soda and Vinegar Work?
They are mild and safe, but they do little to hair. The fizz can loosen a thin film near the top of the drain, and that can help with a faint smell. It will not clear a hair mat or reach the trap. Pull the hair out first, then use the mixture, then flush with hot water. Do not use it right after a chemical cleaner, and never mix those two. If the smell returns within days, the buildup is farther down, and our drain cleaning service can reach it.