Why does my shower drain smell? Here’s how to fix it

You step into the bathroom and cop a whiff of something foul coming up from the shower. Or maybe the water pools around your feet every time you have a wash. The shower looks clean. The water still drains fine. So what is causing the stink?

Smelly and slow shower drains are dead common in Melbourne homes. Most of the time the fix is straightforward. Sometimes it points to something bigger going on underground. Here is what causes it, what you can try yourself, and when to give us a call.

What the smell tells you

The type of smell is a decent clue about what is going on below the grate.

• Musty or mildew-like means mould or biofilm in the drain.
• Rotten egg or sulfur means sewer gas getting past a dried-out P-trap.
• Raw sewage means something has properly gone wrong - a broken seal, a cracked vent, or a blockage deeper in the line.
• Stale or stagnant means hair, soap and body oils sitting in the pipe and breaking down.

If your nose is telling you it is sewage, do not put it off. That smell is a plumbing fault, not a cleaning job.

Why does my shower drain smell?

A stink coming from your shower drain means something is off below the grate. There are a few usual suspects.

Hair, soap scum and body oils

Over time, hair, soap residue, dead skin and oils from shampoo and conditioner collect inside the drain. This gunk forms a sticky layer that breeds bacteria. The bacteria break it down and release gas. That is the smell. Hair tangles with soap residue and forms a thick plug a few inches down the pipe - if the shower is also draining slower than usual, this is almost certainly the cause.

Mould and bacteria

Shower drains are dark, wet and warm. Perfect conditions for mould and bacteria to thrive. As they grow they release gases that give off a musty, rotten stink that gets worse when the water is running. Mould spores release gas that can be harmful if inhaled over time. A small patch can be cleaned with a mould-specific cleaner from your local supermarket. If it covers a larger area, keeps returning, or creeps up the silicone or grout, you need a plumber to check the pipe.

Biofilm build-up

Biofilm is a slime filled with bacteria and bacterial waste that coats the inside of your shower drain and tiles. It looks like a clear or grey jelly and it stinks. It produces a mildew-like smell and can harbour Salmonella, E. coli and other nasties.

You can usually feel it if you push a finger or a brush a couple of inches down the grate - if it comes back coated in slime, that is your problem. To remove it, use a brush or scraping tool and move it in and out of the drain to clear as much slime as possible. Spray the area with an antimicrobial cleaner and leave it for a few hours.

Dry P-trap

If the smell is coming from a shower that has not been used in a while, the P-trap has probably dried out. The P-trap is a U-shaped bend in the pipe that holds a small amount of water. That water acts as a seal against sewer gas. No water, no seal, and the gas rises straight into your bathroom.

This is the most common cause in guest bathrooms, holiday houses and any shower that does not get daily use. Run the tap for 30 seconds and the smell should clear. If it does not, pour two cups of water down the drain and wait an hour. Shine a light down the drain - if you can see the water sitting there, the problem should resolve. If you cannot see water, or the smell comes straight back the next day, the trap may be cracked or the vent pipe blocked, and you will need a professional drain inspection.

Sewer gas

If your shower drain smells like raw sewage, the cause could be more serious. A cracked vent pipe, a broken seal at the waste connection, or a blockage deeper in your sewer line can all let sewer gas escape into the house. So will old pipework that has shifted over time, which is dead common in Melbourne homes built before the 80s. This type of smell will not sort itself out.

You can spot a plumbing fault by the giveaways:

• The smell is strong and obvious, not subtle.
• More than one drain in the house smells or drains slowly.
• You hear gurgling from the drain when water runs elsewhere in the house.
• You have already cleaned the drain and refilled the trap and it has made no difference.
• There is water staining on the ceiling below the bathroom (which usually means a hidden leak).

If any of those apply, stop trying to fix it from the top. The cause is further down and you need proper diagnostic gear.

Drain clog

A telltale sign of a clogged drain is that your shower drains slowly, or not at all, with an odour accompanying the poor drainage. Common culprits include soap scum, hair, dirt and small items. A hand auger can be used to fish out debris, but use it carefully to avoid damaging pipes. If in doubt, call your local plumber.

What to try first

Before calling anyone, work through these. They cover the easy 90% of cases.

1. Run the tap for 30 seconds. Refills the P-trap if it has dried out.
2. Pour a kettle of boiling water slowly down the drain. Loosens soap scum and biofilm.
3. Pull off the grate and clean what you can reach with a drain brush and antimicrobial spray.
4. Use a manual drain snake to pull out any visible hair or gunk.
5. Wait 24 hours and see if the smell returns.

If the smell is gone, stick a mesh strainer over the drain to stop it building up again and you are done. If it returns within a few days, the cause is past where a home tool can reach.

What to do when your bathtub won’t drain

A bathtub that will not empty or drains painfully slowly is usually caused by one of these:

Common causes

• Hair and soap tangled together in the waste pipe, gradually choking off the flow.
• Residue from bath oils, salts and other products clinging to the pipe walls and trapping debris.
• A blocked vent pipe stopping proper airflow in the plumbing system, which slows drainage or causes gurgling.
• Old or misaligned pipes that have sagged or shifted over the years.

What you can try at home

Pour a kettle of boiling water slowly down the drain. This can dissolve soap scum and loosen light build-up.

Try a plunger. A few firm pumps can shift small clogs sitting close to the surface.

Use a drain snake. A basic manual snake from Bunnings can pull out hair and gunk from deeper in the pipe.

If you have tried all three and the water still will not budge, or the drain blocks up again within a week, the problem is further down the line. A damaged pipe or a blockage deeper in the system needs proper gear to diagnose. We use CCTV drain cameras to find exactly what is going on before we touch anything.

Preventative maintenance tips

A few simple habits will keep your drains clear and stop the smell from coming back.

Use a drain strainer

Stick a mesh strainer over the shower drain to catch hair before it goes down the pipe. They cost a couple of dollars and save you from most blockages.

Keep oils and greasy products to a minimum

Bath oils and heavy conditioners leave residue that sticks to pipe walls and traps everything else. If you do use them, flush the drain with hot water afterwards.

Clean regularly

Wipe around the drain and keep soap scum off the shower floor. A quick scrub of the tiles once a week makes a difference.

Use enzyme-based cleaners

Skip the harsh chemical drain cleaners. Enzyme-based products use natural bacteria to eat through organic build-up in the pipe. They are gentler on your plumbing and safer for the environment. Once a month is plenty.

If you want to know more about why we recommend staying away from chemicals, read our guide on why you should avoid chemical drain cleaners.

When to call Drainpro

DIY fixes handle the simple stuff. But if the problem keeps coming back or gets worse, you need a pro. Here is when to pick up the phone:

• The shower drain smells like sewage or rotten eggs even after you have cleaned it
• More than one drain in the house is blocked or smelly
• You have tried the home remedies and the issue returns within days
• Water is backing up into the shower or bathtub
• You hear gurgling sounds from the drain, which usually means a blockage further down
• There is water staining on the ceiling below the bathroom

We carry high-pressure water jetters and CCTV cameras on every truck. We find the problem, show you the footage, and fix it on the spot in most cases.

With over 25 years in drain cleaning and repair, no plumbing problem is too complex for our team.

Need a hand with a smelly shower or a blocked bath? Call us on 1300 303 247 or fill in our online contact form. We service all of Melbourne from our Oakleigh and Essendon depots and we do not muck around.

FAQ

Why does my shower drain smell even if it is not clogged?

Usually bacteria, mould, or a dry P-trap. Organic gunk builds up inside the pipe over time and creates odour even when water drains fine. If the shower has not been used recently, run the tap for 30 seconds to refill the P-trap.

Why does my shower drain smell like sulfur or rotten eggs?

A sulfur or rotten egg smell almost always means sewer gas. The P-trap has dried out and the water seal that normally blocks gas from rising has gone. Run the tap for 30 seconds. If the smell does not clear within an hour, the trap may be cracked or the vent pipe blocked. Either way, you need a plumber.

Why does my bathroom smell like sewage even after cleaning?

If cleaning has not worked, the smell is coming from somewhere you cannot reach. Usually a broken seal at the waste pipe, a cracked vent, a blockage further down the line, or tree roots in the underground pipework. A CCTV drain inspection will show exactly where the fault is.

Can a smelly shower drain make you sick?

The bacteria in biofilm and mould can cause respiratory irritation, headaches and stomach issues over time. Sewer gas in small amounts is unpleasant but not dangerous. In larger amounts it can cause dizziness and nausea. Either way, it is not something to live with.

Is it safe to use chemical drain cleaners?

Most off-the-shelf chemical cleaners are harsh on pipes and not great for the environment. Bleach kills surface bacteria but does not shift biofilm properly, and it damages rubber seals and older pipework. Enzyme-based cleaners work well for regular upkeep because they actually eat the organic build-up rather than mask the smell. For a serious clog, call a plumber rather than reaching for the chemicals. You will save your pipes in the long run.

How do I clean out a bathtub drain?

Start by flushing with boiling water. If that does not shift it, pull out any visible hair with a drain snake or use a plunger. For stubborn blockages, professional drain cleaning is the safest way to clear it without damaging the pipe.

Why is my bathtub not draining at all?

A complete blockage is usually caused by a thick build-up of hair, soap scum, or product residue. Sometimes a blocked vent pipe or old plumbing is the culprit. If basic fixes do not work, a CCTV inspection will show exactly where the problem sits.

Shower drain smells but not clogged - what do I do?

If water drains fine but the smell persists, the problem is usually biofilm build-up, mould, or a dry P-trap. Clean the drain with a brush, spray with antimicrobial cleaner, and run the tap to refill the P-trap. If the smell returns within days, call a plumber to check for deeper issues.

How do I stop my shower drain from smelling in the future?

Stick a mesh strainer over the drain to catch hair. Pour a kettle of hot water down the drain once a week. Use an enzyme-based cleaner once a month. That keeps biofilm from forming and stops the smell coming back.

Why does my shower drain smell worse in summer?

Heat speeds up bacterial growth and dries P-traps out faster. A smell that has been mild all year often gets stronger in January and February for both reasons. Running the tap for 30 seconds twice a week in summer keeps the trap topped up.