Rotten egg smell in the bathroom: identify and remove it

Emergency quick fixes

1. Flush the P‑trap: Run hot water for 60 seconds. If the sink or shower is rarely used, add a tablespoon of mineral oil to slow evaporation.
2. Drain shock: Pour a kettle of hot water mixed with a small amount of mild detergent down the smelly drain; follow with cold water for 30 seconds.
3. Clean the stopper and overflow: Remove hair and biofilm from the pop‑up stopper and scrub the overflow opening with a bottle brush.
4. Water heater test: If the smell is only with hot water, it may be the anode rod. Temporarily set the heater to 140°F for 2–3 hours to pasteurize (then return to normal). Consult your manual first.

Decision tree: find the source fast

1. Hot vs. cold test: Smell only on hot? Focus on the water heater anode and water chemistry. Smell on both? Go to drains and traps.
2. Single fixture or whole bathroom? One smelly drain points to biofilm; multiple drains suggest a vent issue pulling traps.
3. Intermittent with weather? If odors follow storms or windy days, suspect venting and pressure changes.
4. Odor at toilet base? Inspect the wax ring; reseat/replace if the toilet rocks or bolts are loose.

Water heater anode: what to know

Magnesium anodes can react with certain water chemistries and encourage sulfur‑producing bacteria, creating hydrogen sulfide in hot water lines. A safe test is to temporarily set the heater to 140°F for 2–3 hours to pasteurize (restore your normal setting afterward and consult your manual first). If the smell improves, ask a plumber about switching to an aluminum‑zinc anode or a powered anode.

Deep clean the drain assembly

1. Remove the pop‑up stopper; scrub it with dish soap and a brush.
2. Feed a bottle brush with soapy water into the overflow channel and scrub thoroughly.
3. Flush the P‑trap with a kettle of hot water and a little mild detergent; finish with 30 seconds of cold water.
4. For showers/tubs, lift any hair catchers and clean the trap arm with a plastic drain brush.

Maintain monthly to prevent biofilm from rebuilding. This pairs well with tablet treatments to reduce downstream odor compounds.

Preventive routine that actually sticks

• Every month, clean stoppers and the overflow channel; it takes 5 minutes with a bottle brush.
• Run water in little‑used guest fixtures for 60 seconds; add a teaspoon of mineral oil to slow evaporation.
• After vacations, do a quick “trap tour” of the house to refill and check for gurgles.

These tiny habits prevent most bathroom sulfur smells and keep your septic system happier downstream.

Likely causes

• Biofilm in the drain: Bacteria digest organic matter and release hydrogen sulfide.
• Dry or siphoned trap: Without water in the trap, sewer gas enters the room.
• Water heater anode reaction: Magnesium anodes can foster sulfur‑producing bacteria in some water supplies.
• Vent issues: Poor venting may pull water out of traps (gurgling sound).

Whole‑home odor or odors in multiple rooms? Start with septic smell in house. To keep odors down long‑term, see septic treatment tablets and our treatment comparison.

Step‑by‑step diagnosis

1. Hot vs. cold test: Run cold water only — smell gone? Run hot water — smell returns? Suspect the water heater anode.
2. Source isolation: Smell only from one drain? Clean the stopper, overflow, and trap arm biofilm.
3. Trap verification: Shine a flashlight into the drain — do you see standing water? If not, refill and monitor.
4. Vent check: If drains gurgle elsewhere when you empty the sink/tub, a vent restriction is likely.

Prevention & maintenance

• Clean stoppers and overflow channels monthly.
• Keep traps wet in guest baths and basement showers.
• Consider an aluminum‑zinc anode rod if your water chemistry frequently creates sulfur odors (consult a plumber).
• Use a monthly tablet treatment to reduce hydrogen sulfide generation downstream.

FAQs

Why is the smell only with hot water?

The water heater’s magnesium anode can encourage bacteria that create hydrogen sulfide. Testing hot vs. cold isolates this quickly.

Is bleach safe to pour down drains?

Bleach can harm septic bacteria and corrode metals. Prefer hot water + detergent for biofilm, and mechanical cleaning.

Can a clogged vent cause sulfur smell?

Yes — vent restrictions can siphon traps dry, letting sewer gas into the room.