Quick Answer:

If you hear gurgling from the bathroom sink while the shower is running, it usually means air is being forced through water in the sink trap because the drain system is partially restricted or venting is poor. Start with simple checks and a direct comparison to narrow the cause; many issues are fixed without calling a plumber, but some need professional help.

Why This Happens

When the shower sends a large flow of water into the drain system, it can push air and water through connected pipes. If a drain line, p-trap, or vent is blocked or partially clogged, that air can bubble through the sink and make a gurgling sound. Common causes:

• Partial clog in a shared drain line that slows water flow.
• P-trap losing its seal because air pressure is changing when other fixtures drain.
• Blocked or poorly functioning venting (roof vent) that prevents air from moving freely through the plumbing.

If you see similar behavior in other situations, read about Random bubbling from sink or about cases where the sink reacts to appliance drains like the washing machine at Sink gurgles when washer drains.

Step-by-Step What to Do

1. Observe and compare

• Run the shower and drain the sink to compare effects. Note whether the gurgle happens only while the shower is running or also when other fixtures are used.
• Try running the shower at different temperatures and flow settings — does the noise change?

2. Check nearby fixtures

• Flush the toilet and run other sinks or the washing machine to see whether the noise travels through the system or is specific to the shower-to-sink interaction.
• If multiple fixtures show similar signs, the problem is likely in a shared drain or vent.

3. Clean the sink trap and drain

• Place a bucket under the p-trap, loosen the slip nuts, and remove the trap to clear hair and debris. Reassemble carefully and test again.
• If you’re not comfortable doing this, skip to when to call a professional.

4. Try a plunger on the sink

• Use a cup plunger (sink plunger) to apply a few firm plunges while the drain is covered to try freeing a partial clog farther down the line.
• A plunger is safer than pouring chemical drain cleaners, which can damage pipes and are less effective on some clogs.

5. Check roof vents and high stacks (if safe)

• If you can safely access the roof, look for obvious blockages (leaves, bird nests). Don’t climb if conditions are risky.
• Blocked vents are a common cause of pressure problems that make sinks gurgle when other fixtures run.

6. Re-test

• After each action, run the same comparison: turn on the shower and the sink to see if the gurgling stops or changes.
• If the problem persists despite clear traps and plunging, it’s likely further in the system.

What Not to Do

• Do not keep running the shower if backups start. Stopping flow prevents sewage or dirty water from overflowing into living spaces.
• Avoid using strong chemical drain cleaners as a first fix; they can damage pipes and create hazardous conditions if a professional needs to work on the line.
• Don’t climb onto the roof without proper safety gear and experience; call a pro for vent inspection if you’re unsure.

When to Call a Professional

• Persistent gurgling after cleaning the p-trap and plunging suggests the clog or vent issue is deeper in the main drain or branch line.
• If backups or slow drainage appear in multiple fixtures, or if there are odors that suggest sewage, call a licensed plumber.
• If vent access is needed on the roof and you’re not comfortable with heights, hire a pro to inspect and clear vents safely.

Safety Notes

• Turn off water sources or stop the shower immediately if you see backups to avoid overflows.
• Use gloves and eye protection when removing a trap or using a plunger; wastewater can contain bacteria.
• If you must go on the roof for vent checks, use proper fall protection and avoid working on wet or icy surfaces.

Common Homeowner Questions

• Why does the sink gurgle only when the shower is on? — The shower’s higher flow can push air through a partial clog or a poorly vented line, making the gurgle appear only then.
• Can I clear this myself? — You can often clear simple blockages by removing the trap and using a plunger; deeper clogs usually need a plumber.
• Is this an emergency? — Not always, but stop using fixtures if you see sewage backups or strong odors and call a pro promptly.