If you’re referring to the viral car-care tip “put a glass of salt in your car,” the idea is usually to use salt to absorb moisture from the air and help reduce condensation or dampness inside the vehicle.
Does it work?
Salt is hygroscopic, meaning it can attract and hold some moisture. However, an ordinary glass of table salt isn’t a particularly effective car dehumidifier, especially in a humid environment. Commercial moisture absorbers containing calcium chloride or silica gel generally work much better.
If your car has condensation
Try these instead:
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Make sure the air-conditioning system is working properly. A/C removes moisture from cabin air even when you’re using warm air for defogging.
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Use the defrost/defog setting when windows fog up.
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Check for wet carpets, floor mats, or leaks around doors, windows, and the trunk.
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Don’t leave wet umbrellas, clothing, or towels inside the car.
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Use a purpose-made automotive moisture absorber if the cabin stays damp.
One important warning
Don’t put an unsecured glass container of salt in your car. It can tip over and spill, potentially damaging interior surfaces or electronics. If you want to try a moisture absorber, use a stable, enclosed product designed for that purpose.
So the “surprising reason” is essentially moisture control, but the viral trick is more gimmicky than a guaranteed solution.
