Why Does My Bathroom Smell Like Rotten Eggs?

Rule out gas if plausible, then compare drains, hot water and the toilet area.

Updated September 15, 2026Safety-aware troubleshootingNo professional inspection implied

Quick answerA rotten-egg bathroom smell can be drain gas, hot-water sulfur odor or — if gas service/equipment is nearby — odorized natural gas. Do not assume every sulfur smell is 'just the drain.' First decide whether the room air itself smells independent of running water.

Act before troubleshootingIf natural gas is plausible, leave and call from a safe location without operating switches or phones in the leak area.

60-second diagnosis

Does the room smell before any water runs?
Is gas equipment or a gas line nearby?
Does only hot water smell?
Is one drain clearly strongest?
Does the toilet base smell worse after flushing?

Likely causes, ranked by fit

Drain/trap sewer odor

Common

Best fit: Strongest at one drain and changes after running water.

How to check: Refill little-used traps and inspect drain buildup.

What fixes the source: Restore trap seal/clean accessible buildup.

Hot-water sulfur odor

Possible

Best fit: Odor appears only when hot water runs and at other hot fixtures.

How to check: Compare hot/cold.

What fixes the source: Water-heater evaluation.

Toilet seal / venting issue

Possible

Best fit: Worse near toilet base or after flushing; gurgling may occur.

How to check: Check stability and fixture interactions.

What fixes the source: Plumber repair.

Fuel gas

Rule out

Best fit: Room air smells regardless of water/drains, gas source nearby.

How to check: Leave and call from safe location.

What fixes the source: Gas utility/emergency service.

What to do now

Rule out gas if plausible.
Compare hot versus cold water.
Refill unused drains.
Check toilet stability and gurgling.

Do not do this

Do not light matches or use a flame to identify the source. Do not mix drain cleaners.

When to call a professional

Gas emergency service if plausible; plumber for recurring drain/toilet/vent symptoms.

Questions people ask

Why does it smell only during showers?

If only hot water triggers it, the heater/water supply may be involved. If the drain itself smells as water hits it, buildup or trap/vent issues are more likely.

Can a dry drain smell like rotten eggs?

Yes. Sewer gas is often described as sulfur-like. A dry trap is a common pathway.

Is carbon monoxide the smell?

No. Carbon monoxide is odorless. A CO alarm should be treated separately and urgently.

Primary safety/reference sources used on this guide

U.S. PHMSA — Recognizing and responding to natural-gas emergencies — Natural gas is odorized and may smell like rotten eggs; PHMSA advises leaving the area and avoiding switches, phones, flames and engines near a suspected leak.
CDC — Carbon monoxide poisoning basics — Carbon monoxide is odorless and colorless; smell cannot confirm or rule out CO.

This information is educational and cannot verify a leak, electrical fault, mold condition, water quality result, plumbing-code issue or appliance failure remotely. When there is immediate danger, follow local emergency guidance.