I use peppermint oil in my house to help keep mice out of the kitchen cupboards. I've found ground pepper is a good deterent too along with white vinegar. I live on a lake and have a stone foundation with a dirt crawlspace. You don't need to use a lot of the oil for it to be effective. I've talked with my vet in the past regarding Cassie and she sees no harm so long as I don't over do it. I take a wet paper towel dab a drop of oil on it and wipe down the areas in the drawers and cabinets. Inside closets at the baseboard is a good place to wipe down too along with under sinks inside vanities and toilets. If you have an access panel to the pipes for your shower or bath wiping in there and leaving damp towels with oil helps too. The odor is not over powering this way, just leaves a nice light scent in the room. If you know where the mice are coming in, usually around pipes or any small crack in the walls take the damp paper towel with the oil and fill the area around the pipes. The towel hardens blocking the entrance point and the mice won't chew through it because of the peppermint. Cable wires leave a nice gap in the wall so wipe around them too. A drop on a peppermint tea bag works well too thrown into the back of cupboards. I do the same thing with vinegar. Ground pepper black or cayenne sprinkled liberally inside and under ovens will keep them out of there and doesn't smell bad when cooking. I've had them nest inside the insulation in the stove. Very embarrassing moment when we had the repair man in for the smoking stove. When he removed the top there were pellets, seeds and nuts baking in there. Since my dogs passed on I now use poison in the crawlspace. This in itself is not 100% so I continue to monitor upstairs and use the home remedies up there. I use the large rat blocks so they are not carried upstairs. None of these is a one time cure, I redo everything when needed. During the winter it's a monthly if not weekly chore and for some reason spring brings them back. If you look around where you have seen them you can follow their droppings back to their nest or entry point into the room. The entry point will normally be in a dark area and there will be increased droppings where they come in along with an occasional pellet or nut shell.
Good luck.

Nancy & Cassie BE2