Why Does My Shower Drain Smell Bad?

A shower drain that smells is usually not a sewer problem, which is the first reassuring thing to know. In most cases the source is a few inches inside the drain and can be dealt with in an afternoon. The distinction worth making early is what kind of smell it is.

Musty and sour, or sewage?

A stale, sour, faintly rotten smell that is strongest right at the drain, and worse when you first run the water, points to material inside the drain itself.

A smell that reads clearly as sewage, that fills the room rather than sitting at the drain, or that comes and goes without any pattern of use, is a different problem. That is sewer gas entering the room, and it means a trap or a vent is not doing its job.

The first is a cleaning job. The second needs investigating.

The usual cause: biofilm

Shower drains collect hair, skin, soap residue and shampoo. That mixture coats the inside of the drain and the top of the trap, stays permanently damp, and supports bacterial growth. The smell is a by product of that growth.

It builds up gradually, which is why the smell tends to creep in over months rather than appear one morning. It is also why it usually returns on a similar cycle if only the surface is cleaned.

A hair mat makes it considerably worse, because it holds organic material in place and stops it washing through.

A trap that has dried out

Every drain has a trap holding standing water, and that water is the only thing separating your bathroom from the drain system. If it evaporates, there is nothing in the way.

This is common in a shower that has not been used for weeks, in a guest bathroom, or in a house standing empty. It is the first thing to rule out because the fix is to run the water for a minute or two and see whether the smell goes.

A trap that dries out again within days, in a shower being used normally, is not evaporating. Something is pulling the water out, and that points at venting.

Cleaning it properly

Surface cleaning rarely fixes this, because the material sits below the grate where nothing reaches it.

Take the cover off. Most shower grates lift out or come away with one or two screws. Everything useful is underneath.

Remove the hair. A barbed plastic strip or a bent length of stiff wire will pull out what is there. This is the single biggest contributor and the part most often left in place.

Scrub the walls of the drain. An old toothbrush or a narrow bottle brush, as far down as it will comfortably go. The coating is what smells, so it has to come off physically.

Flush it through. A kettle of hot, not boiling, water and a little dish soap will carry away what you have loosened.

If the smell returns within a week or two of a thorough clean, the source is further down the pipe than you can reach.

Things blamed on the drain that are not the drain

A few bathroom smells get attributed to the drain because that is the obvious suspect.

Mold or mildew behind or beneath tiles produces a persistent musty smell that does not change when you clean the drain. Failed grout or sealant lets water behind the surface, and the smell comes from what is growing there.

A shower used rarely can also smell simply from damp and poor ventilation, which is not a plumbing fault at all.

If cleaning the drain thoroughly changes nothing, it is worth stepping back and considering these before going further into the pipework.

When the smell points further than the fixture

Some patterns suggest the drain is not really the source.

More than one fixture smelling, a smell that is stronger in the room than at the drain, gurgling from other fixtures, slow drainage alongside the odor, or a smell that worsens in wind or heavy rain all suggest sewer gas rather than buildup. So does a trap that empties repeatedly in a shower being used normally, which usually means a vent problem is siphoning it.

Sewer gas indoors is worth dealing with rather than living with. Our article on what gurgling indicates covers the venting side, and sewer and drain services covers the wider system.

Keeping it from coming back

A hair catcher over the drain prevents most of what causes the problem, and emptying it is a great deal easier than clearing the drain later.

Running water briefly in a shower that goes unused keeps the trap full. Flushing the drain with hot water occasionally helps, and letting the bathroom ventilate after use reduces the damp that everything else depends on.

When to bring someone in

Reasonable triggers are a sewage smell that persists after the drain has been cleaned thoroughly, several fixtures affected, a trap that keeps emptying, gurgling or slow drainage alongside the smell, or any sign of water where it should not be.

For blockage related odor, see drain cleaning.

Frequently asked questions

Why does my shower smell worse in hot weather?

Warmth speeds up the bacterial activity producing the smell, and it also speeds evaporation from a trap in a shower that is not used often. Both make an existing problem more noticeable rather than creating a new one.

Is a smelly shower drain dangerous?

Buildup inside a drain is unpleasant rather than hazardous. Persistent sewer gas in a room is a different matter and is worth resolving promptly, particularly in a small bathroom with little ventilation.

Will pouring bleach down the drain fix it?

It may mask the smell briefly, but it does not remove the coating the bacteria are living in, so it usually returns. Physical cleaning works better. Never mix bleach with other drain products, as the combination can produce hazardous gas.

For plumbing service in Houston, call (877) 563-1074 to connect with an independent plumbing service provider.