Why Your Bathroom Sink Stinks Like Sewer or Rotten Eggs?

Ever notice that foul, rotten egg or sewer smell in your bathroom? You're not alone.

This unpleasant odor isn't just a nuisance; it can make your bathroom feel dirty and, more importantly, signal a potential issue with your plumbing.

Understanding the cause is the first step, and often, fixing it is simpler than you think. Let's dive into the common reasons behind that disgusting smell and how to resolve them.

What's That Smell? The Rotten Egg or Sewer Stench Explained

That foul, sulfuric smell isn't just unpleasant — it's a red flag. There are typically two main culprits:

1. Hydrogen sulfide gas (H₂S): smells like rotten eggs and is produced by bacteria in drains or sewer systems.

2. Sewer gas: a mixture of various gases (including methane and H₂S) escaping from your plumbing due to a faulty seal or dry trap.

   
   

These gases are not only revolting but can be mildly toxic. Moreover, they can be flammable in high concentrations, although dangerous levels in home bathrooms are rare. Still, you don’t want to be breathing it in regularly.

🌐 A recent study published in ScienceDirect confirms that microbial colonies in drain systems produce hydrogen sulfide and other odorants as they metabolize organic matter (ScienceDirect, 2025).

Warning: Prolonged exposure to hydrogen sulfide gas can be harmful. If symptoms like dizziness occur, ventilate your bathroom and consider calling a professional plumber.

5 Common Causes of a Smelly Bathroom Sink

There’s no one-size-fits-all answer, but here are the most likely reasons your bathroom sink stinks like rotten eggs:

1. Dry P-Trap

The most common and easiest-to-fix issue. The P-trap is that U-shaped pipe under the sink that holds a small amount of water. It blocks sewer gases from coming up. If the sink hasn’t been used in a while (like in a guest bathroom), the water can evaporate. Further leaving an open path for those smells.

2. Bacterial Growth in the Drain

Biofilm — a slimy buildup of bacteria and gunk — can accumulate inside your sink’s drainpipe. As this organic material breaks down, it emits sulfur-like odors. This is especially common if you’ve poured oils, hair products, or soap down the drain over time.

3. Clogged or Slow Drain

A partial clog can trap debris like hair, toothpaste, or soap scum. This sludge becomes a breeding ground for odor-causing bacteria.

4. Vent Pipe Blockage

Your plumbing system includes vent pipes that release sewer gases outside the home. If those vents become blocked by debris (like leaves or a bird’s nest), the gases can be pushed back into your bathroom through the sink.

5. Leaky Drain or Pipe

Cracked or loose pipes can allow sewer gases to escape behind your walls or under your sink. Sometimes the issue is not visible until the odor becomes impossible to ignore.

Simple Fixes to Try 

Before you grab the phone to call a plumber, there are several low-effort fixes you can try:

a. Run Water in the Sink

If you haven’t used the sink in a while, run the water for 1–2 minutes. This will refill the P-trap and restore the water seal.

Tip: Pouring a cup of pink RV antifreeze into the drain can also help keep the trap from drying out in unused sinks.

b. Clean the Drain with Baking Soda and Vinegar

• Mix ½ cup of baking soda followed by ½ cup of white vinegar 

• Pour it down the drain. 

• Let it fizz and sit for 15 minutes. 

• Rinse with hot water.

  
  

This will kill bacteria and break down biofilm, which will help eliminate the smell at the source. Learn more about how to clean with this combo in our guide to cleaning bathtubs with baking soda and vinegar.

c. Use a Drain Brush

Physically scrubbing the inside of the drain pipe can loosen and remove built-up gunk that may not flush out with water alone.

d. Flush the Overflow Hole

Don’t forget the overflow hole (that small slot near the rim of the sink). It can collect bacteria and mildew. Use a pipe cleaner with vinegar to flush it out.

When to Call a Professional?

Sometimes, no matter how much you clean or try DIY fixes, the smell just won’t go away. It can be a sign of deeper issues like hidden pipe damage, vent blockages, or mold growing in hard-to-reach places.

In such cases, it's best to call a professional plumber in your area.

Final Thoughts

A smelly bathroom sink is your plumbing's way of waving a red flag. Whether it's a dry P-trap, bacterial buildup, a vent blockage, or a hidden leak, addressing the issue promptly is key.

Start with the simple solutions; often, a little attention and basic care can solve the problem. If the stink persists, don't hesitate to call in a professional. You deserve a bathroom that smells fresh, not foul.