Inevitably, it happens—your child spills milk on the car seat, the milk in the upholstery turns sour and you can't get rid of the horrible smell. Although sour milk stains and the obnoxious odour related to the stains seem impossible to remove, several easy-to-obtain cleaning ingredients and tools can quickly disperse the stain and smell.
Mix two parts vinegar to one part water in a spray bottle to make a cleaning solution.
Take the car seat out of the car and place it on the ground.
Spray the vinegar and water solution on all milk-stained areas, or even the entire car seat. Wait 15 to 20 minutes for the solution to soak into the upholstery fibres.
Clean the upholstery with a wet vac steam cleaner and carpet/upholstery solution. Allow the car seat to air-dry. If you can still smell sour milk, go to Step 5.
Combine three to five drops of tea tree oil and three cups of water in another spray bottle.
Apply the tea tree cleaning solution to the entire car seat—upholstery and plastic pieces.
Wait 25 to 30 minutes, then rinse the car seat upholstery using the wet vac with water instead of cleaning solution. In addition, wipe the plastic or other nonfabric portions of the seat with a damp, lint-free microfiber cloth.
Air-dry the seat and place a bowl of baking soda in your car overnight to soak up any sour milk odours lingering in the car.