How to get mildew smell out of a car, and skunk, urine and other smells

A musty, moldy or "wet" smell means water is sitting somewhere, usually in the carpet pad where you cannot see it. "The key to mold control is moisture control" (EPA): a spray that leaves the water in place cannot fix it.

The A/C smells musty when it starts

Water on the evaporator behind the dash grows "bacteria and mold" if it sits. Turn the A/C off and "let the fans run for a few minutes" before you switch off the car, and replace the cabin air filter (Consumer Reports). If it keeps coming back, have the drain checked. A MINI bulletin traces "a foul smell (musty, rotten, and vinegary) when the A/C is first turned on" to a drain hose not draining; the fix was to restore drainage and clean the evaporator (MINI SI M64 01 17).

Visible mold or a flooded car is past a DIY smell job: the leak or flood damage needs a mechanic or body shop first.

Consumer Reports' rule for a car interior is no bleach and no hydrogen peroxide, "because they are likely to damage your car's upholstery" (Consumer Reports). The two exceptions below, a freshly mixed peroxide solution for skunk and CDC's bleach solution for mouse mess and vomit, are narrow: hard plastic and rubber mats only, never upholstery, carpet, leather, Alcantara or screens.

Six of the seven main ingredients in skunk spray are sulfur-containing thiols (Nebraska Extension). The spray also carries thioacetates, which "slowly get hydrolysed by water, releasing the nauseating thiols" (University of Bristol): that is why the car smells again on a damp morning. After running over one, the spray sits on the tires and underside.

How long does skunk smell last on a car?

Left alone, "skunk odor typically declines in intensity over several weeks", and it and "may reactivate during periods of high humidity" (Nebraska Extension). Tomato juice is "ineffective"; wash the source off instead.

Urine soaks into the seat foam, so a clean-looking seat can still smell. Never steam it: "The heat will permanently set the stain and the odor by bonding the protein into any man-made fibers" (Humane World for Animals).

The front passenger seat often holds an airbag occupant sensor; check your manual. Hyundai says the seat must be "completely dried before driving" or "the airbag warning light may illuminate or malfunction" (Hyundai).

On leather, wipe it up fast and follow leather car seat cleaning. If urine has reached the foam, a mobile car shampoo with extraction gets further than any spray.

The cleanup, child seats included, is in how to remove vomit from a car seat: CDC's bleach solution (CDC) on hard plastic and rubber mats only, a disinfectant labeled for fabric and extraction on seats and carpet.

How long the smell lasts. We found no published figure for how long a vomit smell stays in a car, so treat any number of days you read as a guess. What decides it is whether residue is left:

• Residue extracted, fabric fully dry: the source is gone, and what lingers in the air should clear as the car airs out. EPA's rule for indoor air is to "reduce or remove the sources of pollutants and to ventilate" (EPA).
• The smell returns on a hot afternoon: some residue is probably still in a seam, the foam or the carpet pad. Our reasoning, not a measured result: a hot cabin makes whatever is left smell stronger. Seats in sun-parked cars averaged 123°F after one hour in an Arizona test on days over 100°F (ASU and UC San Diego, 2018), and interior material emissions track surface temperature (Zhang et al., PNAS Nexus, 2024). A car that smells fine at 8 am and sour at 3 pm probably still has a source.
• A damp, musty smell after the shampoo: the fabric or pad is still wet. Get it dry: EPA says materials dried within 24 to 48 hours will in most cases not grow mold (EPA).

When to go again. A smell that survives a dry, aired car needs a second pass at the source, not more freshener: an enzyme cleaner per its label, enough to reach as deep as the vomit went, then extraction and full drying. A fog or an ozone treatment comes last, for what is left in the air and the vents once the source is gone; it doesn't replace the clean (can ozone get rid of cigarette odor).

Fish smell is trimethylamine, made when "bacteria and fish enzymes convert TMAO into trimethylamine (TMA)"; acids such as lemon or vinegar "cause TMA to bind to water and become less volatile" (American Society for Nutrition). Remove the source, wipe hard surfaces and rubber mats with diluted white vinegar or lemon juice (test first, not on leather), extract any soaked carpet and air the car. Next time, use a sealed cooler in the trunk.

Mouse smell is urine, droppings and nests, sometimes in the air intake or cabin filter. Here "vacuum first" is wrong: "Don't vacuum or sweep rodent urine, droppings, or nesting materials. This can cause tiny droplets containing viruses to get into the air" (CDC).

New car smell is gases from new plastics, foams, adhesives and leather, and heat drives it. In a one-month-old car in a Beijing summer, emissions tracked "material surface temperature rather than the air temperature", and formaldehyde exceeded China's cabin limit in 37.5% of measurements (Zhang et al., PNAS Nexus, 2024). Sun heats those surfaces fast: in an Arizona test on 100°F-plus days, dashboards in sun-parked cars averaged 157°F after one hour (ASU and UC San Diego, 2018).

It fades slowly: in two cars, new-car odorants were still present after 23 weeks of use (Buchecker et al., Indoor Air, 2022). Park in shade, drive the first minutes with windows down, and skip fresheners.

Quick fix or deep clean?

A quick fix (remove the item, air the car, a new cabin filter) is enough when nothing is wet or soaked. If the smell returns on a hot or damp day, the source is still in the foam, the pad or the A/C and needs extraction. EPA: "The most effective ways to improve your indoor air are to reduce or remove the sources of pollutants and to ventilate" (EPA). Dog hair: how to remove pet hair from a car.