Why does my kitchen sink smell like rotten eggs only when I run hot water?

Hot water can accelerate the breakdown of organic matter in your pipes, releasing hydrogen sulfide gas faster. If the smell appears only with hot water, it’s often a sign of biofilm or grease buildup that’s being heated up. Run cold water first to see if the smell persists, and then focus on cleaning the drain walls and trap, as described in Checks 1 and 2.

Can a dry P-trap cause a rotten egg smell in my kitchen sink?

Yes. A P-trap holds a water seal that blocks sewer gases. If the trap is dry—because the sink hasn’t been used for a few days, or the trap is cracked—sewer gas can enter your kitchen. Refill the trap by running water for a minute. If the smell returns after a few hours, inspect the trap for cracks or a faulty vent that might be siphoning water out.

Is it safe to use chemical drain cleaners to fix a rotten egg smell?

Chemical drain cleaners are generally not recommended for odor issues. They can damage PVC pipes, and they often only mask the smell by clearing clogs temporarily. More importantly, they can be harmful if mixed with other cleaners. For odor problems, mechanical cleaning (like a drain brush) and hot water flushes are safer and more effective. If you suspect a sewer gas leak, call a professional instead.

How can I tell if the smell is from the drain or from the garbage disposal?

Run the water and smell near the sink rim, then place your hand near the disposal’s splash guard. If the smell is stronger when the water is off, it’s likely the disposal. You can also run a few cups of ice through the disposal (with water) to dislodge debris. If the smell persists, clean the splash guard and the disposal chamber with warm soapy water, as described in Check 3.

Why Does My Kitchen Sink Smell Like Rotten Eggs? A Practical Checklist

Start Here: How to Use This Checklist Without Overlooking a Step

A rotten egg odor from your kitchen sink is rarely a single, obvious problem. The smell usually points to one of three culprits: sulfur-producing bacteria in biofilm, decomposing grease trapped in the drain, or a failing plumbing vent that allows sewer gas to back up. Because each cause requires a different fix, working through a checklist in order saves time and prevents you from treating the wrong issue.

Begin with a simple observation test. Run cold water for 30 seconds and note whether the smell fades, intensifies, or stays constant. Then run hot water for the same time. A smell that worsens with hot water often points to grease or biofilm, while a smell that appears only after heavy use or when the water is off suggests a sewer gas issue. Write down your results—they will guide which checklist items matter most.

This checklist is designed for a typical double or single kitchen sink with a standard P-trap. If you have a garbage disposal, a dishwasher connected to the drain, or an older home with galvanized pipes, you will need to pay extra attention to the items marked for those setups. Always work with the power off when inspecting electrical components, and if you ever smell gas, leave the house and call a professional immediately—this checklist does not cover gas leaks.

Check 1: Inspect the P-Trap for Stagnant Water and Biofilm

The P-trap—that curved pipe under your sink—is designed to hold a small amount of water that blocks sewer gases from rising into your kitchen. If the trap is dry, cracked, or improperly installed, that water seal disappears, and you get a direct path for rotten egg smells. A common cause of a dry trap is a sink that hasn’t been used for several days, especially in a guest bathroom or a seasonal kitchen. Run water for a minute to refill the trap and see if the odor disappears.

Even if the trap holds water, biofilm can coat its inner walls. Biofilm is a slimy layer of bacteria that feeds on soap scum, food particles, and even the minerals in your water. As these bacteria break down organic matter, they release hydrogen sulfide gas—the same compound that gives rotten eggs their smell. To inspect, place a bucket under the trap, unscrew the slip nuts (or call a plumber if you’re unsure), and look for dark, greasy sludge. If you see it, cleaning the trap manually with a stiff brush and warm soapy water is the most effective fix.

If the trap looks clean but the smell persists, check the trap’s gaskets and alignment. A misaligned trap can create a small gap that lets air in, breaking the water seal. Also, check whether the trap is vented correctly. Some older homes have a drum trap or an S-trap, which are more prone to siphoning and drying out. If you have one of these, consider consulting a plumber about replacing it with a modern P-trap that meets current codes.

Check 2: Scrape and Flush the Drain Walls to Remove Grease Buildup

Grease is a major contributor to kitchen sink odors because it coats the drain pipe walls and traps food debris. Over time, this greasy layer turns into a thick, rancid film that harbors odor-causing bacteria. Unlike biofilm, which is slimy and often located near the trap, grease buildup tends to be more widespread, extending down the horizontal run toward the wall. A quick visual check won’t reveal it—you need to feel for it.

To test for grease, dip a long-handled brush or a flexible drain brush into the drain and pull it back out. If the bristles come back coated in a brownish, greasy residue, you have a grease problem. Flushing with hot water alone won’t remove it, but you can loosen it by pouring a kettle of boiling water down the drain in two stages, waiting 30 seconds between pours. Be careful with boiling water if you have PVC pipes—check your local plumbing codes, but most modern PVC can handle 140°F (60°C) water without issue.

For stubborn grease, use a mechanical method rather than a chemical cleaner. A drain auger or a plumber’s snake can physically scrape the walls as it travels down. Alternatively, a mix of coarse salt and ice cubes run through a garbage disposal can help scrub the disposal’s interior, but this won’t reach the pipe walls. If you have a dishwasher connected to the sink drain, check the dishwasher’s discharge hose—it often has a loop that can collect grease and create a backup. Clean the hose and the connection point where it meets the sink drain.

Check 3: Inspect the Garbage Disposal and Dishwasher for Food Traps

A garbage disposal is a common hiding spot for food particles that rot and produce hydrogen sulfide. The disposal’s grinding chamber has crevices and a rubber splash guard that can trap small pieces of food, especially if you don’t run water long enough after use. A quick test: with the power off, shine a flashlight into the disposal and look for stuck particles, mold, or a slimy film on the rubber gasket. If you see buildup, remove the splash guard (if removable) and clean it with warm soapy water.

Dishwashers can also be the source of the smell, even though they aren’t directly under the sink. If your dishwasher drains into the sink’s drain line, food particles can travel up the hose and sit in a low spot, where they decompose and release gas that travels back up through the sink drain. Check the dishwasher’s air gap—a small device on the back of the sink—and remove any debris. Also, run a cup of white vinegar through an empty dishwasher cycle (with no dishes) to clear grease and food residue from the interior and hoses.

If you have a garbage disposal, never put coffee grounds, eggshells, or starchy foods like pasta down it—they are notorious for creating a paste that clings to the walls. Instead, run cold water for 15 seconds before and after using the disposal, and always use it with a steady stream of water to flush particles through. If the smell persists after cleaning, consider replacing the disposal’s splash guard, as it can be difficult to fully sanitize once it becomes porous.

Check 4: Test for Sewer Gas Leaks and Venting Problems

If biofilm and grease are ruled out, the smell may be sewer gas entering through a broken vent or a dry trap. The vent pipe (which usually exits through your roof) equalizes pressure and allows gases to escape. If the vent is blocked—by leaves, bird nests, or ice—sewer gas can bubble up through the sink drain. To test for a blocked vent, fill the sink halfway with water and pull the stopper. If you hear a gurgling sound or see slow drainage, the vent may be clogged.

You can also perform a simple smoke test with a lit candle. Light a candle and hold it near the sink overflow hole (the small opening near the rim). If the flame flickers or goes out, that’s a sign of air being pulled in through the vent—not necessarily a leak. A more reliable test is to pour a few drops of water into the overflow hole and listen for a slow drain. If the water sits, the vent is likely blocked and you should call a plumber, as climbing on the roof is dangerous.

Another cause of sewer gas is a cracked or loose wax ring on the sink’s drain flange—the part visible inside the sink bowl. If water seeps around the flange, it can carry odors up from the pipe. Inspect the base of the faucet and the area around the drain for moisture. If you find a leak, tighten the flange screws or replace the putty seal. For gas leaks, never use your nose to search—use a commercial leak detector spray (available at hardware stores) and look for bubbles. If you suspect a gas leak, leave the house and call your gas company or a licensed plumber immediately.

Check 5: Clean and Sanitize the Entire Drain System, Then Prevent Recurrence

Once you’ve identified and fixed the primary cause—whether it’s biofilm, grease, or a vent issue—you need to sanitize the entire drain system to eliminate residual odors. A thorough flush with hot water and a mild detergent can remove surface grime, but for deeper sanitization, use a mixture of boiling water and a cup of white vinegar. Pour it down the drain, let it sit for 10 minutes, then flush with hot water. This helps neutralize alkaline and acidic residues that bacteria feed on.

For ongoing prevention, adopt a weekly maintenance routine. Once a week, pour a kettle of boiling water down the drain to melt away new grease, followed by a small handful of baking soda and a cup of white vinegar. Let the mixture fizz for 5 minutes, then flush with hot water. This is different from using baking soda as a deodorizer—it’s a physical action that helps break down buildup. However, avoid using baking soda if you have a garbage disposal, as the abrasive particles can scratch the metal over time.

Finally, consider installing a drain strainer to catch food scraps before they enter the pipe. This simple addition reduces the organic load that bacteria feed on. Also, run water for at least 10 seconds after each use, especially after using the disposal, to ensure all waste is flushed out. If you have a dishwasher, run it on a hot cycle with a cup of white vinegar in a dishwasher-safe bowl once a month to keep the internal hoses clean. Over time, these habits will prevent the rotten egg smell from returning.