Why does my kitchen sink smell? Causes and fixes
A kitchen sink that smells is usually caused by fat and food rotting in the trap and the first stretch of waste pipe. The next most common causes are a dishwasher or washing machine hose that lets dirty water sit or siphon back, a trap that is losing its water seal, and a slow or blocked drain further along. A sour, rotting-food smell points to the trap. A sewer smell, especially with gurgling or slow draining, points to the drain or the seal that keeps drain air out. Start by cleaning the trap. If the smell comes back within days, or you can smell it at other sinks or outside, the cause is further along the pipe.
Loyal Plumbers · Updated
Discuss your plumbing workWhat the smell tells you
Describe the smell honestly, because it narrows things down quickly.
| Smell and pattern | Likely cause | First step |
|---|---|---|
| Sour or rotting food, strongest at the plughole | Fat and food built up in the trap and waste | Clean the trap |
| Smell after the dishwasher or washing machine runs | Appliance hose without a high loop, or dirty water sitting in it | Check the hose route |
| Sewer smell that comes and goes, gurgling when water drains | Trap seal being pulled out, or poor venting | Watch the trap water level |
| Sewer smell plus slow draining, other outlets affected | Blocked waste pipe or drain | Check the outside gully |
| Smell from the cupboard rather than the plughole | Leaking joint or loose trap seal | Look for damp under the sink |
| Smell only from the hot tap water | Water, not the drain | Run water into a glass away from the sink |
Clean the trap and waste
Most kitchen smells come from the trap, the curved or bottle-shaped fitting under the sink that holds water to keep drain air out. Fat from cooking coats the inside, food catches on the fat, and it rots. Pouring more hot water down the sink moves it along a little but does not remove it.
Put a bowl under the trap, unscrew it by hand and empty it. Clean it out with an old brush and washing-up liquid, and look up into the sink waste and along into the pipe towards the wall for more build-up. Check the rubber washers as you go and refit it hand-tight. Run the tap and check for drips before you put things back in the cupboard. Our guide on how to unblock a sink covers the same job when the sink is also slow.
Keep fat out of the sink from now on: wipe pans with kitchen roll and put it in the bin, and use a sink strainer. Thames Water's advice on blockages makes the same point, because the fat that smells in your trap is the fat that blocks the sewer.
Do not mix drain cleaners, or use a chemical cleaner and then open the trap. Some combinations give off dangerous fumes, and caustic cleaners can damage plastic waste and seals.
Check the dishwasher and washing machine hoses
If the smell appears after the dishwasher or washing machine has run, look at how the drain hose is connected. It should rise to a high loop, usually clipped under the worktop, before it drops to the sink waste. If it lies on the cupboard floor, dirty water from the sink can run back into it and stagnate, and some appliances can siphon water out of the trap.
A hose connected to the wrong side of the trap can also let drain air into the kitchen. Our article on washing machine waste and sewer smells explains how appliance connections cause odours, and if either machine is also slow to empty, see our guide on a dishwasher not draining.
When the trap is losing its water
A trap only stops smells while it is full of water. If it is being emptied by siphoning, drain air comes straight into the room. Signs are a gurgle from the plughole after the sink or an appliance empties, and a smell that comes and goes rather than staying constant.
This happens when the waste pipe is long or too small, when a large volume of water pulls the seal out as it goes past, or when the pipework is not vented properly. Some kitchens have an air admittance valve under the sink or in the boxing; if that valve sticks, the same symptoms appear. Our guide on a gurgling sink goes through these checks, and our article on an air admittance valve smell covers the valve itself.
When the drain is the problem
If the sink is slow, the smell is of sewage rather than food, and you can also smell it at the bathroom basin or outside, the waste pipe or the drain is probably partly blocked. Look at the gully outside where the kitchen waste comes out. A gully with a crust of fat, standing water or an overflow tells you the blockage is outside, and cleaning the trap indoors will not solve it.
A sewage smell through the house is covered in our guide to a sewage smell in the house, which explains how to separate a drain fault from a problem with the soil stack or a sealed pipe.
Leaks under the sink
A small leak from the trap, the waste or an appliance connection soaks into the cupboard base and smells musty rather than sewery. Empty the cupboard and feel the base and the back panel for damp. A swollen or stained base usually means it has been going on for a while. Our guide to a leak under the kitchen sink explains how to tell a waste leak from a supply leak.
What a plumber will do
A plumber will take apart and clean the trap and waste, check how the dishwasher and washing machine are connected, watch whether the trap holds its water when appliances empty, and check any air admittance valve. If the smell is coming from further along, they will check the gully and the drain run and clear or survey it. Where the problem is the layout, such as a long run with too little fall or no venting, they will explain what needs to change before replacing anything.
Get the smell sorted
Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road. Call 020 4652 8585 and tell us what the smell is like, when it is worst, and whether the sink or any appliance is slow to drain.
Our call-out charge is £60, and the engineer explains what they have found and what the work involves before starting. You can also read about our kitchen plumbing and drainage work.
Common questions
- Why does my kitchen sink smell like rotten eggs?
- An eggy, sewer-like smell usually means drain air is getting past the trap, either because the trap is being siphoned or because the drain is partly blocked. Run water into a glass away from the sink as well: if the tap water itself smells, the cause is the water, not the drain.
- How do I get rid of a smell from my kitchen sink?
- Unscrew and clean the trap, then clear any fat from the waste pipe you can reach. Check the dishwasher and washing machine hoses rise to a high loop. If the smell returns within days, the cause is further along the waste or in the drain.
- Does bicarbonate of soda and vinegar work?
- It can freshen a slightly smelly trap, but it will not remove a layer of fat or a blockage. Cleaning the trap by hand does more, and a smell that keeps returning needs the cause finding.
- Why does my sink smell after the dishwasher runs?
- The drain hose may not have a high loop, so dirty water sits in it or runs back, or the dishwasher is pulling water out of the trap as it pumps. Check the hose route under the worktop.
- Can a blocked drain outside make my sink smell?
- Yes. If the gully or drain the kitchen waste runs into is blocked, waste water sits in the pipe and the smell comes back up through the sink. The sink will usually be slow as well.
Sources and further reading
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