How long does a dead mouse smell last?
By The Pest GuyLast updated
About two weeks, going by council guidance. North East Derbyshire says the odour can take between 10 to 14 days to disappear, and Clackmannanshire says it is at its worst for up to a week. It gets worse before it gets better, and then it goes on its own. The smell is the part that ends. What it tells you about your house does not.
North East Derbyshire describes the shape of it. It starts faint, gets steadily worse while the body breaks down, then tails off. So if it is stronger today than yesterday, that is the middle of the curve, not a second mouse.
People describe it as rotting cabbage, fish or gas, which is the council's own wording. The two chemicals behind it have names: putrescine and cadaverine, which a body makes as it breaks down. Neither is a clue to where it is. Your nose and the flies are.
Two things stretch the timescale. Damp is one: a US pest-trade training letter puts it simply, the damper the site, the longer the odour will last. Size is the other. The same letter says a single dead mouse may barely smell at all, and several in one spot can be a real problem. If the smell is strong and long, it is worth asking whether it was a rat, and the droppings will usually tell you.
Why you can smell it and cannot find it
Because it died somewhere you cannot get to. That is normal, and councils say so. Charnwood's terms for its own rodent treatments say its officer will not lift floorboards, and that more than likely the bodies are not found. North East Derbyshire says its technician may not be able to get under floors or into awkward lofts either.
The one reliable pointer is flies. Thanet Council says a sudden appearance of bluebottles in the home normally means a small animal has died, possibly under the floorboards or up a chimney. Where they gather is where to look, and what a sudden mass of flies means covers the places a body hides.
If anything was baited in the last couple of weeks, that is very likely the cause. Thanet says bait can take 4 to 12 days to work, which can leave a localised foul smell from the bodies. For rats the distance can be large: the UK rodenticide stewardship code says they may die 100 metres or more from the bait. Poison decides when it dies, not where.
Should you open the wall
Usually not, and in most British houses you cannot sensibly. A piece written for pest technicians in the BPCA's trade magazine makes the point: cutting into a wall void is an option, but not if the body is in or behind a masonry wall. A lot of UK walls are exactly that.
Under a floorboard or in a loft you can reach is different. Lift the board, look, and take it out. Behind brick, the honest options are waiting it out or paying someone to open up a wall to shorten a smell that ends by itself within a couple of weeks. That is rarely good value.
If you are renting, it is worth knowing whose job the mice are before you pay for anything. And if you are quoted to find and remove a body, check what the work should cost first.
Getting rid of the smell while you wait
Air freshener covers it up and nothing more. The trade magazine piece says so plainly: when the fragrance wears off, you are left with the foul smell again. Open windows and keep air moving, which is Charnwood's advice too, and treat the freshener as buying yourself a nicer evening.
A proper deodoriser is different, and North East Derbyshire makes the distinction: unlike air fresheners, it takes the odour out of the air. Enzyme sprays are the other thing you will be sold, and they only work if they touch the body, which means you have to have found it. Skip the ozone machines. The same piece warns that ozone attacks the lining of the lungs.
If you do find it: picking it up and binning it
Gloves on, and do not touch it with bare hands. The NHS says exactly that about dead animals. North East Derbyshire's method is the simple one: pick it up with a spade, shovel or litter picker, double bag it, put it in your black bin, and wash your hands well afterwards. Charnwood says the same.
One council newsletter suggests checking with your own council first, because some have rules about dead animals in household waste. Worth a look at your council's website if you are finding more than one.
Is the smell harmful to breathe
Unpleasant, yes. I could not find a single official UK source that says the smell itself makes you ill. The ones that do say it are pest firms, and they do not cite anything.
The real risk is touching things, not smelling them. The NHS says leptospirosis spreads through the pee of infected animals, rats and mice among them, and that it is rare in the UK. UKHSA says hantavirus is usually caught by breathing in particles from rodent urine, droppings or saliva, and puts the risk to the UK public as very low. So wear gloves, do not stir droppings up into the air, and do not lose sleep over the smell.
The part that does not go away on its own
The smell ends. The gap does not. A mouse dying in your wall means a mouse got into your wall, and Rochdale Council says a gap the diameter of a pencil is enough. Until that is shut, the next one uses the same route. Finding the way in is the job that stops you smelling this again next winter.