Mice enter almost every kitchen through this one hidden spot: an under-$10 fix blocks it completely
Updated on July 22, 2026
If you’ve had a mouse in your kitchen in the last few years, you know the drill. Scratching at night. Droppings behind the trash can. You set a trap, catch one, feel done with it, and a week later there’s another.
Here’s the part almost no one gets told. The mouse you caught was never really the problem. The way it got in was. And in most American kitchens, that way is sitting in plain sight, in a spot you look at every day without really seeing it.
Mice don’t need a hole you can see across the room. According to the Centers for Disease Control and Prevention (CDC), they can squeeze through an opening about the size of a dime (roughly 2 cm across). Emory Matts, a bug expert at Terminix, puts it plainly: “if you can fit a pencil into a crack, hole or opening, a mouse can get through it.” Their skulls squish down. If the head fits, the body follows.
So the real question isn’t whether your kitchen has cracks and holes. It does. The question is which one mice are using.
Why fall is when this starts
These animals don’t hibernate. They have to keep eating and stay warm all winter, or they die. So when the weather turns, they hunt for a way indoors. The window is short and easy to predict.
Robert Pierce, PhD, who studies wildlife at the University of Missouri, says mice can come indoors any time of year, but as it gets colder they look for a warm spot to hide, and what they really need is cover and food. That’s why a house with no mouse trouble all summer suddenly has one behind the fridge in October. Not bad luck. A season.
Once one mouse gets in, more follow. They leave a scent trail others can pick up. Until the entry point is sealed, fresh rodents keep coming through it, no matter how many you trap.
The overlooked spot in almost every kitchen
Walk into your kitchen right now. Open the cabinet under the sink. Push aside the dish soap and trash bags and look at where the drain pipe goes down into the floor, or where the water lines come in through the back wall.
See that little dark space around the pipe? The one that isn’t quite closed?
That little space isn’t a mistake. It’s built that way on purpose. When a plumber runs a pipe through a cabinet floor or wall, they cut the hole a little bigger than the pipe so it has room to move and the job goes faster. Nobody comes back later to fill it. It sits open for as long as the kitchen exists.
The CDC’s official advice on keeping mice out names this spot directly. When they list where to hunt for entry points inside your home, one of the top items is “around the pipes under sinks and washing machines.” The country’s public health agency, telling homeowners exactly where to look.
Sheldon Owen, PhD, who studies wildlife at West Virginia University, says once mice are inside, they chew things, dirty your food, and spread germs through their pee, spit, and droppings. Mice are known carriers of salmonella (a stomach bug that can make you seriously sick), and the CDC says the common house mouse can carry a virus that’s dangerous during pregnancy.
Why this one spot beats every other kitchen entry
There are other ways mice get into houses: cracks under outside doors, holes where cable and gas lines come in, foundation splits. Those matter. But the under-sink hole has three things going for it that make it the easiest door in the whole kitchen.
- It leads straight to food. The cabinet is inches from the trash.
- It’s hidden. A mouse coming in through the front door has to cross open floor with lights and feet nearby. A mouse popping up around a drain pipe comes out behind cleaning supplies, in the dark, near the wall.
- It’s already open. Most outside cracks at least have weatherstripping or trim covering them. This one has nothing. A straight shot from inside the wall to inside your cabinet.
That’s why the CDC lists it. And why you can catch mouse after mouse in the same kitchen without the problem ever stopping. You’ve been treating visitors instead of closing the door.
The fix: two things, under ten dollars, one trip to the hardware store
What actually stops it isn’t a repellent. It isn’t peppermint oil.
The CDC’s own guidance says it in one sentence: fill small holes with steel wool, and put caulk around the steel wool to keep it in place. That’s the whole play. Nebraska Extension backs it up, recommending stainless steel or copper wool for anything smaller than a quarter inch (6 mm). Mice can’t chew through metal. They chew right through spray foam on its own, which is why foam alone doesn’t work, no matter how tempting it looks in the can.
This weekend, do this:
- Grab a pad of steel wool (about $3, or roughly €3) and a tube of caulk made for outdoor use (about $5, or roughly €5). Any hardware store.
- Empty the cabinet under your sink so you can see the floor and back wall clearly.
- Find every spot where a pipe comes through. The drain going down, the hot and cold water lines coming in, plus dishwasher and garbage disposal lines if you have them.
- Stuff the opening tight with steel wool. Push it in with a screwdriver so no loose ends stick out and no light shows through.
- Run a bead of caulk around it to lock the wool in place. This stops mice from pulling it out or working around it.
Do it before the first cold snap. Once mice are already inside, sealing the hole traps them in with you. Seal in fall, before they get in.
While you’re down there, check where the wall meets the floor inside the cabinet. Any daylight, any crumbling caulk, any crack you can slide a pencil into gets the same treatment.
Sources: (1) Centers for Disease Control and Prevention, How to Seal Up to Prevent Rodents; (2) Centers for Disease Control and Prevention, Hantavirus Prevention; (3) Emory Matts, Terminix, quoted in Real Simple; (4) Robert Pierce, PhD, University of Missouri Extension, quoted in Southern Living; (5) Sheldon Owen, PhD, West Virginia University Extension, quoted in Southern Living; (6) University of Nebraska Extension, House Mouse Prevention and Control