Mice, rats and stored classic cars

Rodent damage to cars is common and getting more expensive. Aviva reported in October 2025 that its motor claims for rodent damage rose by 28% in 2024, with the average claim reaching £2,494. Which? reported the same figures, and noted that most comprehensive policies will pay for rodent damage, though cover varies. Cars that stand for long periods are most at risk: Aviva advises keeping a rarely used car in a secure place such as a garage, and the RAC advises checking any car that has not been driven for a week or more.

Mice need only a small gap. The British Pest Control Association (BPCA) says a mouse can get through a gap of 5mm, about the width of a pencil's rubber end, and a rat through 15mm. A car has many openings of that size.

• Up the tyres and onto the suspension. Most rodents reach a car by climbing the wheels and tyres.
• Through the bulkhead. Gaps around cables, pedal shafts and the steering column lead from the engine bay into the cabin.
• Through the air intakes and grille. Fresh-air intakes and heater ducts lead to the heater box, a warm, enclosed space that makes an ideal nest.
• Into the air filter housing. Air cleaners on many classics have open intakes, and filter material makes good bedding. The RAC has reported a car that lost power because an animal had stored food in its air filter box.
• Through the exhaust. A tailpipe is an open tube into the car's structure.
• Through drain holes and the spare wheel well. Holes in the floor, the boot and an underslung spare wheel give access from below.
• Through open windows, a gap in a hood, or an unlatched boot.

Rodents' front teeth never stop growing, so they gnaw constantly. In a car they damage:

• Wiring. Chewed insulation can leave wires bare, causing short circuits, warning lights, failed lights and, in the worst case, a fire. The BPCA notes that rats can cause serious fires by gnawing the insulation around electrical cables.
• Fuel, brake and vacuum pipes. Aviva lists fuel and water leaks from bitten tanks and pipes among the damage it sees in claims; Hagerty UK mentions nibbled-through fuel pipes.
• Upholstery and trim. Seats, carpets, seat belts, door cards and headlinings are torn up for nesting material. On a classic, original trim can be hard or impossible to replace.
• Insulation and sound deadening, which is shredded for nests.
• Air filters and heater boxes, which become nests and food stores.

What about "soy-based" wiring?

You may read that some modern cars use wiring insulation made partly from soy, and that it attracts rodents. This has not been proven. A US class action against Toyota over rodent-damaged wiring in 2012 to 2016 models was dismissed in 2018; the company said it knew of no evidence that rodents are attracted to soy-based insulation, and that rodent damage affects all makes. Rodents gnaw wiring of every kind, including the wiring in classic cars.

The risks are small, but they are real, and they are easy to reduce.

Leptospirosis (Weil's disease)

Leptospirosis is a bacterial infection spread in the urine of infected animals, including rats and mice. It enters the body through cuts and grazes or through the lining of the mouth, nose and eyes. The UK Health Security Agency (UKHSA) recorded an average of 57 laboratory-confirmed and 89 probable cases a year in England between 2020 and 2023. Most people have no symptoms or mild, flu-like illness, but some people become seriously ill, and the severe form, known as Weil's disease, needs urgent treatment. There is no vaccine for people.

See a GP if you develop a high temperature, headache, diarrhoea, red eyes or loss of appetite after possible contact with rodent urine, and say that you have been cleaning up after rodents. Ask for an urgent GP appointment or contact NHS 111 if you have yellowing of the skin or eyes, a rash, are unable to pass urine, or have swollen ankles, feet or hands, chest pain or shortness of breath.

Hantavirus

Hantaviruses are carried by rodents and spread mainly by breathing in tiny particles from their dried urine, droppings and saliva. The strain found in the UK is Seoul virus, which has been found in pet rats and, occasionally, in wild rats in a few areas. UKHSA describes the risk to the public as very low, and Seoul virus does not spread between people. The cleaning advice below is designed to stop particles from droppings getting into the air.

Other infections

The BPCA notes that mice and rats can also spread Salmonella and Listeria through their urine and droppings.

UKHSA's advice is clear on one point above all: do not sweep or vacuum up mouse or rat urine, droppings or nests. Dry sweeping and vacuuming put particles into the air you breathe. Wet the mess first, then wipe it up.

1. Air the car. Open the doors, boot and bonnet and leave it for 20 to 30 minutes before you start. (This step is from the US Centers for Disease Control and Prevention, whose guidance includes vehicles.)
2. Protect yourself. Wear rubber household gloves. UKHSA suggests a suitable dust mask, such as an FFP1 or FFP2, is ideal. Cover any cuts with waterproof plasters.
3. Wet it down. Spray droppings, urine stains and nests with water, then with a household disinfectant, until damp, and leave the disinfectant to soak for about five minutes.
4. Wipe it up. Use damp kitchen paper or wet wipes. Lift out soaked nest material carefully.
5. Bag it. Seal everything in a plastic bag and put it in an outside bin.
6. Clean the area again with disinfectant and let it dry. Test any disinfectant on a hidden part of upholstery or carpet first.
7. Remove your gloves and wash your hands thoroughly with soap and water.

Only use a vacuum cleaner once everything has been wetted, disinfected and wiped up. A nest in a heater box or in the ducting may need parts of the dashboard or heater removing; if the heater fan blows a smell or debris when switched on, look before you use it again.

Pest controllers agree that keeping rodents out is far more effective than dealing with them once they are in. None of these steps is expensive.

Take away food and bedding

• Clear the car. Remove every crumb, sweet wrapper and dog biscuit, and vacuum the carpets before the car is laid up.
• Clear the garage. Bird seed, pet food, grass seed and compost are all rodent food. Store anything edible in metal bins or sealed hard containers, or move it out of the garage.
• Remove nesting material. Rags, cardboard boxes, old blankets and piles of newspaper make bedding. Keep the garage tidy so there are fewer places to hide.

Proof the building

• Find the gaps. Check at floor level first, where mice are most likely to get in, and around pipes, cables, vents and the garage door.
• Seal them with materials rodents cannot chew. The BPCA recommends wire wool set in quick-setting cement for holes. The RSPCA warns that caulk, rubber and plastic fillers do not work, because rodents chew through them. Fine metal mesh works for vents and larger openings.
• Seal the door. The BPCA recommends a brush strip or door sweep where the gap under a door is more than 4mm.

Proof the car

• Cover the openings. Fit fine metal mesh behind the grille and over air intakes where you can do so without blocking airflow when the car is used.
• Block the tailpipe and air intake for the winter, using a plug or a bung made for the purpose. Avoid plain wire wool for long periods in a damp garage, because it rusts.
• Tag every blocker. Put a brightly coloured tag on each plug and a note on the steering wheel listing them. Starting an engine with the exhaust or intake blocked can damage it.
• Close the windows if there is any chance of mice. Use moisture absorbers inside the car to deal with damp instead of leaving windows open.
• Keep the bonnet closed.

Keep an eye on it

Visit the car regularly. A car that is looked at every week or two gives you early warning: droppings on the floor, shredded paper or a smell are easy to deal with in October and costly in March.

Many products and home remedies claim to keep rodents away. The evidence for most of them is weak.

Ultrasonic devices

Plug-in devices that emit high-pitched sound are widely sold. A 1995 review for the US Department of Agriculture's National Wildlife Research Center found that controlled tests of commercial ultrasonic devices showed only marginal effects, a 30 to 50% reduction in movement, and that rodents got used to the sound quickly, with no significant effect after three to seven days. A University of Arizona extension review of the research reached a similar conclusion: rodents showed a mild aversion at first, which faded over time. Ultrasonic devices are not a reliable way to protect a stored car.

Peppermint oil and other smells

Peppermint, eucalyptus and spearmint oils are often suggested, and the RSPCA lists oil-soaked cotton wool as a gentle deterrent at entry points if it is replaced regularly. The scientific evidence is mixed. A 2016 systematic review of plant compounds as rodent repellents found inconsistent results across laboratory, enclosure and field studies. Peppermint does no harm, but do not rely on it.

Mothballs

Do not use mothballs. Naphthalene, the traditional mothball chemical, has been prohibited for use in pesticides since 2008, and it is illegal to supply naphthalene mothballs in the UK. The Government's product safety reports describe naphthalene as a banned, carcinogenic substance that can cause irreversible damage to internal organs if swallowed or inhaled, and trading standards warn that it is highly flammable. Filling a closed car with its fumes is a bad idea whatever the product.

Dryer sheets, soap and other remedies

Tumble-dryer sheets, strong soap and similar remedies appear in many lists of tips. We found no published trials showing they keep rodents out of cars. Treat them as unproven.

Light and activity

Rodents prefer dark, quiet places. Hagerty UK suggests lighting the garage over winter, and a car that is used or visited often is less likely to be colonised. These help, but they are not a substitute for proofing.

If rodents are already in the garage, traps are the safest way for an owner to deal with them.

Break-back (snap) traps

A well-made break-back trap kills quickly, and the RSPCA says that kill traps of this kind can be considered humane if they are well built and work properly.

• Place them where rodents run, close to walls and at right angles to them, so the trigger can be set off from either direction. Droppings show where they travel.
• Put them in a tunnel or box. Pest control industry guidance recommends purpose-built boxes or narrow run-through tunnels, which make the trap more effective and keep birds, pets and children away from it.
• Bait them well. The BPCA suggests nutty chocolate or raisins rather than cheese.
• Check them regularly. Pest control industry guidance links regular inspection to the duty of care in the Animal Welfare Act 2006. If you cannot check a trap, lift it.

Live-capture traps

Live-capture traps catch the animal unharmed. They must be checked frequently, as the RSPCA advises, because an animal left in a trap suffers. Releasing the animal elsewhere is less kind than it sounds: the RSPCA notes that, as far as it is aware, no study has followed what happens to released rats and mice, and that other rodents show very high death rates when moved to unfamiliar areas.

Glue traps

Do not use glue traps. They are banned for use by the public throughout Great Britain: in Wales since 17 October 2023, in England since 31 July 2024 (where only licensed professional pest controllers may use them, in exceptional circumstances), and in Scotland, where using, supplying or possessing one has been an offence since 1 July 2026. The RSPCA regards them as indiscriminate and inhumane.

Poison is the option most likely to cause problems in a stored car, and it is best left to professionals.

What the public can buy

Rodenticides sold to the public are restricted. Products for amateur use must contain a lower strength of active ingredient and are sold only in small pack sizes in their original packaging. The strongest products are for professionals, and those authorised for use outdoors are sold only under the UK rodenticide stewardship regime, where the buyer must show proof of competence. The BPCA warns that, because amateur products are restricted, you may not be able to buy a poison that will work, and that almost all house mouse populations in London, and possibly in other cities, are resistant to traditional rodenticides.

The risks

• Children, pets and other animals. The Health and Safety Executive (HSE) notes that children, pets and other non-target animals are more likely to be harmed by rodenticides than by many other pesticides, and that the common anticoagulant poisons present higher risks than are normally accepted. Users are legally required to take all reasonable precautions to keep other animals away from bait.
• Wildlife. Predators and scavengers that eat poisoned rodents can be poisoned in turn. Rodenticide residues are found in a wide range of wildlife, including barn owls.
• Dead rodents in the car. Anticoagulant poisons do not kill at once. The industry code of best practice warns that poisoned rats can die 100 metres or more from the bait. In a garage, a poisoned mouse may crawl into the heater box, a sill or behind the trim and die where it cannot easily be found or removed.

If you use poison

Read and follow the label exactly. Use bait only inside tamper-resistant bait boxes, never loose. Search for and safely dispose of dead rodents during and after treatment, and remove any uneaten bait at the end, so it does not remain available to wildlife. Never put bait inside the car.

The BPCA recommends contacting a professional pest control company for any mouse or rat infestation. Call one if:

• you see signs of rodents in the car itself, or repeatedly in the garage despite proofing and traps;
• you find rats rather than mice;
• the garage is attached to the house, or connects to roof spaces or wall cavities;
• you need poison used safely around children, pets or wildlife.

A professional can survey the building, find the entry points and use products the public cannot buy. The BPCA's website has a search tool for member companies, who are trained, insured and follow a code of practice.

Before the first start in spring, and on any visit through the winter:

• Look for droppings on the floor around the car, on the engine, under the bonnet, in the boot and under the seats.
• Smell the cabin. A strong, stale smell of urine is often the first sign.
• Check the air filter and its housing for nests, droppings or stored food.
• Look at the wiring in the engine bay, under the dashboard and in the boot for bare copper or chewed insulation.
• Inspect fuel, brake and vacuum pipes for tooth marks.
• Run the heater fan briefly with the windows open before driving. Debris or a smell means there is a nest in the heater box or ducting.
• Remove all plugs and blockers you fitted, and check the tags against your list.

If you find damage to wiring or fuel or brake pipes, have it repaired before the car is driven. Chewed wiring can cause a fire, and a chewed fuel or brake pipe can fail on the road. Tell your insurer promptly if you intend to claim.

For the full list of jobs when laying a car up, see winter lay-up step by step and the printable checklist. A dry garage helps here too, see damp and condensation, and the main storage guide covers everything else.