Quick Answer:
A persistent bad smell coming up from the bathroom sink drain usually means trapped organic matter, a dry or leaking P‑trap, or sewer gas entering the room. Start with a few simple checks and a warm water flush to see whether the odor changes immediately. If basic cleaning doesn’t stop the smell, call a plumber—especially for sewage-like odors or repeated problems.
Why This Happens
- Debris, hair and soap scum collect in the drain and create bacterial growth that smells as it breaks down.
- A dry or leaking P‑trap (the curved pipe under the sink) can let sewer gas come up. If the trap has lost water, gases escape easily.
- Blockages farther in the drain or a problem in the sewer line can create stronger, sewage-type odors. If the smell seems isolated to the sink, see Sewer odor only in sink for related scenarios and checks.
Step-by-Step What to Do
1. Do a quick visual and smell check
- Look at the sink stopper and around the drain for visible gunk, mold, or standing water.
- Smell at the drain opening to confirm the odor is coming from the sink and not a nearby fixture or vent.
2. Flush the drain with warm water
Flush the drain with warm water and note whether odor increases immediately. A rise in odor right after flushing may mean trapped material is being disturbed or sewer gas is being pushed up through a flawed trap.
3. Run hot water for a minute
- Let hot tap water run for at least 60 seconds to loosen grease and soap build-up.
- Follow with a short cold rinse to help carry loosened debris down the line.
4. Clean the stopper and visible drain parts
- Remove the pop-up stopper or strainer (most pull out) and wipe away hair and gunk. A small brush or old toothbrush works well.
- Reassemble and test the smell again.
5. Check the P‑trap
- Place a bucket beneath the P‑trap and remove it if you’re comfortable doing so to inspect for standing debris or leaks.
- Clean the trap and reassemble carefully. If the trap was dry, filling it will often stop sewer gas.
6. Use a safe cleaner if needed
- Try an enzyme drain cleaner or a mix of baking soda followed by vinegar, then flush with hot water. These break down organic matter without strong fumes.
- A mechanical snake can clear deeper clogs; avoid pouring large amounts of harsh chemical drain cleaners into confined spaces.
7. Re-test and observe
- After cleaning, flush with water and note whether the smell returns or disappears.
- If the odor returns within a day or is stronger after flushing, that’s a sign of a deeper issue that needs a professional inspection.
What Not to Do
- Do not ignore strong odors assuming they will fade on their own.
- Do not mix household cleaners (for example, never mix bleach and ammonia) — dangerous gases can form.
- Avoid pouring large volumes of strong chemical drain cleaners into a sink unless recommended by a professional; they can damage pipes and create hazardous fumes.
When to Call a Professional
- Call a plumber if the smell is clearly like sewage, returns after cleaning, or if you find a leaking trap or damaged pipe.
- If the problem affects multiple fixtures or you notice slow drains throughout the house, that suggests a main sewer issue.
- If the odor follows a pattern (for example, stronger at certain times of day) and basic fixes don’t work, consider professional help—especially for scenarios like Sink smells only at night.
Safety Notes
- Work in a well-ventilated area. Open a window or run an exhaust fan when using cleaners.
- Wear gloves and eye protection when removing debris or working under the sink.
- Do not mix cleaning chemicals. If you use a commercial product, follow the label instructions and disposal directions.
- If you suspect methane or strong sewer gas and feel dizzy or unwell, leave the area and call for professional help immediately.
Common Homeowner Questions
Why does the sink smell like rotten eggs?
Rotten-egg odor often means hydrogen sulfide from bacterial breakdown of organic matter or sewage gas; cleaning the trap and drain usually helps.
Can I use bleach to fix the smell?
Small amounts of diluted bleach can disinfect surfaces, but it won’t remove physical debris; enzyme cleaners and mechanical cleaning are safer long-term options.
How long should a smell-free result last after cleaning?
If the source was surface debris or a dry trap, the smell should be gone until new buildup occurs; recurring odor within days suggests a deeper problem that needs a plumber.