Why Does My Bathroom Sink Smell?

No one ever wants to deal with a smelly bathroom sink: for the strength of the stench emitted is far stronger than anybody’s zeal to push through with their skin care routine.

Shortly afterwards, you’ll find yourself sitting in a cramped position in the kitchen scrubbing your face with a colloidal oat mask.

A smelly bathroom sink like any other issue at home isn’t without its own causes too. For starters, you can take it as a butt-kick warning from your ancestors to start getting serious with your in house hygiene: if you’re the type that really needs such advice.

Meanwhile in this article, we’ll explain to you the many different reasons why your bathroom sink keeps emitting an unbearable stench every single time you use it.

What causes a bathroom sink to smell?

  1. Evaporation of water in the P-Trap.
  2. Nasty buildups in the P-Trap and other plumbing pipelines.
  3. Leaks in or around the P-Trap.
  4. Blocked or Broken Vent Pipe.
  5. Blockage in Sewer Line.

Now that we’ve quickly gone through the main causes of a smelly bathroom sink, let us revisit each one of them separately to fully understand how they may cause such complication.

Evaporation of water in the P-Trap

Ever used a bathroom sink that has been around for a long time without use and got a breeze of offensive odor smacked directly into your nostrils? Or opened the doors to your master bathroom after a very long winter break but quickly noticed the strange atmosphere inside.

Part of the causes is the evaporation of water inside the P-Trap mechanism which is located underneath the sink’s plumbing in your bathroom. The P-Trap has the prefix “P” attached to it for a reason. It’s the shape of the pipe when viewed at an angle which resembles the capital letter P. Such under sink mechanism is made to look like that for a very good reason.

The U shaped bend, which is the trap of the mechanism, allows the P-Trap to retain a little amount of water whenever the sink is drained, and this water acts to prevent most of the sewer gas from coming up the drain pipes and out through the sink by virtue of its denser nature compared to the sewer gas. The gas, having no route to follow via the P-Trap, is forced to follow the natural plumbing paths provided for it which are the drain vents.

Depending on whoever is using the bathroom sink often, your sewer gases can be a complex combination of toxic sewer gases capable of causing damage to organs or respiratory irritation. Aside methane which is the most dominant representative found inside the sewer gas, other toxins such as ammonia and sulfur dioxide can easily become a part of it from every day habits of disposing various kinds of chemicals such as skin care products down the drain

When the water in you P-Trap evaporates, no medium exists to serve as a barrier between the sewer gas and your drain. As a result, the gas make its way up to the drain and overwhelm the entire space when it comes out.

How to fix the issue: Run water continuously for about 30 seconds or more to refill the U shape. This should prevent gases from coming out through the drain going forward. If its winter period, and the smell still comes back again, chances are that the water has frozen. You want to run water continuously for about 1 minutes and then pour down an antifreeze to keep the retained water from freezing.

Nasty buildups in the P-Trap and other plumbing pipelines

Because of the U shape of the P-Trap, it becomes susceptible to debris, junk and waste accumulation. Overtime, these can reach a significant level in the trap and begin to rot, emitting a stench that is awakened every time you drain water from the sink.

That’s why it’s especially helpful to avoid disposing semi-solid foods like porridge, mashes of different veggies and starches etc., into your bathroom sink. You should also ditch the habit for vomiting inside the bathroom sink as the vomit contains solids that can be retained in the U shape or other under sink plumbing.

How to fix the issue: Use a plunger to get the stuck particles out from the P-Trap. If that doesn’t work, consider hiring a license plumber to check the issue for you. Or, if you do know what you’re doing, you can disassemble the under sink plumbing and empty their contents yourself.

Leaks in or around the P-Trap

Because a P-Trap serves to prevent sewer gas from coming through the drain holes using water as its main barrier, a leak in it can actually cause the reverse to happen. A small drop in the amount of water present in the P-Trap can cause gases to escape and be perceived inside the bathroom.

If you complain of a smelly bathroom sink, you want to inspect the P-Trap for leaks in or around it by yourself or using the help of a licensed professional plumber.

Blocked or broken vent pipe

The job of the vent pipe is to regulate the air pressure in your plumbing system. With this mechanism in place, the right pressure is provided that enables wastewater to be carried along the drain pipes to the septic tank or city sewer, and the gases that make their way up from the sewer and water waste are removed through the pipes to the atmosphere.

As you would expect, a damage incurred in the vent piped, whether a blockage or crack would result in effects that are reflected inside the house, and in this case, the bathroom.

How to fix the issue: Inspect for a broken or blocked vent pipe using the help of a licensed professional or by yourself and make sure to replace or fix it.

Blockage in sewer line

Blockage in sewer lines are a much bigger issue than drain pipes as they require more work and of course money, and sadly this can also be the cause of your smelly bathroom sink. When your sewer line blocks due to some reason, it means that there would be an obstruction in the path of wastewater flowing, so some of these can be backed up in several drain lines throughout your home. These back ups alongside the smelly gas they carry, can actually make their way into the P-Trap and from there leak out from the drain and overwhelm the bathroom.

How to fix the issue: Seek the help of a professional plumber.


A smelly bathroom sink can have different causes. It may be that the water in the P-Trap has evaporated which gives room for sewer gas to leak into the bathroom space, or the P-Trap itself has leaks in or around it which drops the water level in it and cause a leakage of sewer gas.

Other reasons can be a clogged P-Trap that emits the stench of the wet matter that make up its clog. A broken vent pipe that interferes with the proper drainage of waste forcing gases out through the drain, or a broken sewer line that causes waste to back up into P-Traps and release an offensive smell.

Whichever it is, it’s best to always consult a professional plumber so you can solve the problem effectively and efficiently.