A family member of mine (who, out of embarrassment, wishes to remain anonymous) recently had an incident of the pongiest proportions. It involved a two-litre bottle of milk mistakenly left in her car for an entire weekend in the hot summer sun.

The result: an explosion that covered the front passenger side of her car in milk that curdled and seeped into the upholstery. Along with the maggots that wriggled out from her carpet, it left a foul, pungent smell that would just not go away.

While it isn’t always a detonating milk carton, most of us have been in a similar situation – one that leaves a lingering stink in our car.

Professional crime scene cleaner and the director of Clean Queens, Gabrielle Simpson, says the most common bad smells in cars are from spilt takeaway coffee, or windows left down after rain which leads to excess moisture in a car’s carpets and fabrics. The hot, wet weather much of Australia is experiencing certainly isn’t helping keep that new car smell either.

Simon Cook, who is a partner at Star Car Wash, says that bacteria in the air conditioner unit, cigarette smoke, body sweat, stale food left in difficult-to-locate crevices or any liquid or wet food spillage – especially milk and seafood – are also quite common sources of stink.

“Always clean the contaminant before it gets the opportunity to generate an odour,” he says.

But if the smell has already set in, Simpson says you should “remove, wash and rinse out the cause of the smell. This usually means a steam clean machine and high-powered wet and dry vacuum.”

Importantly, do not just mask the smell. “Using any type of masking spray is just that, it will mask a smell it will not eliminate it,” she says.

To effectively remove a bad smell, you need to look at what exactly is causing it and where it is, then employ the right strategy depending on the source.

Pet smells

If you are a pet owner or carer, it’s always better to protect the car interior than to remedy the smell. Seat and floor coverings can help with this.

But if the damage is already done, Cook’s advice is to “steam clean where the damp hairs are more readily removed from the upholstery. At home, a vacuum with a power head can help.”

Milky spills

Mop up the milk or coffee as soon as possible, preferably with an absorbent paper towel or microfibre cloth. Blot the stain rather than rubbing it, as rubbing can cause the liquid to penetrate further into the fabric.

After this, “the most effective process is to use a powerful extraction system to suck out the liquid. It will be also necessary to rinse the area with water to thoroughly flush the milk from where it has been,” Cook says. This could be done at home with an enzyme-based cleaner, or through a professional service.

For set milk stains, Cook suggests a steam cleaning tool to break down the hardened residue. “In some cases, it may be necessary to remove the affected seats and carpet in order to gain access to where the milk has run.”

Body fluids

Whether it’s sweat, vomit or something else, accidents happen – especially if you have kids. “Safe removal of any excess fluids off a carpet or upholstery is a start,” Simpson says.

“Diluting a small amount of ammonia with water and patting it over the fabric or carpet will help break down any protein out. Apply pressure to the spill using something super absorbent like a towel.”

But if you don’t have the time, or just want the best outcome, Simpson recommends engaging a carpet and upholstery cleaner to steam clean and deodorise the fabrics and carpets.

Cigarette smoke

The smell of cigarettes is often the trickiest to remove, because the smoke particles can reside nearly anywhere within a car.

The managing director at All Aces Cleaning and Restoration, James Wright, suggests using sugar soap on the hard surfaces, and recommends changing the air filter of your car. “It is inexpensive and easy to replace.”

But the odour can still sometimes hang around, in inaccessible locations within the car. If this is the case, the help of a professional car cleaner is probably required.

“The process usually involves a complete detail where every internal surface is either wiped down or steam cleaned,” says Cook.

Mould

Mould occurs when fungal microbes meet spilled liquid or dropped food on an interior surface and begin to grow.

“The best option is to wipe away any of the mouldy patches with an anti-bacterial product. This should also include steam cleaning all fabrics,” says Cook. This is because “the heat helps kill the spores”.

“The most important final process is to then let the car fully dry with the doors open before use.”