Why do I get condensation on car windows? What causes windows to steam up in morning, and how to demist them

Advice on why car windows steam up, the quickest way to defog them and how to stop it happening

The fall in temperatures as we ease into autumn means more difficult conditions for drivers.

Road conditions make driving trickier and cars are more susceptible to breakdowns but one of the most common and frustrating experiences is the appearance of condensation on your car windows.

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It’s often the case first thing in the morning as you’re setting out on a journey, but a car’s windows can fog up at any time and whenever it occurs it poses a risk to you and others. It can even land you in trouble with the police if your vision is obscured.

So it’s worth understanding why condensation forms on car windows as well as how to clear it and the steps you can take to stop it happening in the first place.

Why do car windows fog up?

The “fog” on your car windows is condensation formed when warm moist air comes into contact with the cold glass surface. The heat from your body and breath warms the air inside the car and increases the moisture levels. When this air then comes into contact with the cold glass, it condenses and causes the mist or fog on the windscreen and windows.

The best way to demist your windscreen

Wiping the window with a clean cloth or demisting pad is a quick fix but won’t stop more condensation forming and can leave streaks so it’s better to use the ventilation system if you can.

Make sure the air is directed at the windscreen and windows, and turn the fan up full. Keep the temperature low to start with - overloading the car with hot wet air will just add to the moisture problem. The cold air from the fans will still be warmer than the glass and help dry it out then you can start to turn up the heat.

If you’ve got air conditioning, put this on. It will help to dry the air out more quickly.

Don’t use recirculation. This will warm the car quicker but keeps the moisture trapped inside.

Instead, open the window. Especially if you don’t have air con or climate control, this will help clear the screen faster. The cold dry air from outside will help reduce the moisture inside and then you can start to raise the temperature.

How to stop your windows fogging up

Clean your windows - removing tiny dirt particles gives the water less to cling to, lessening the condensation

Don’t leave wet items in the car - coats, umbrellas, dog towels etc just add to the moisture problem and mean mist will be more likely to form and take longer to clear.

Check for leaks - Even a small leak allowing damp to find its way into your car is enough to cause problems by making the air damper. Check areas such as window and door seals to make sure no water is creeping in, and check carpets and upholstery aren’t damp.

Use a dehumidifier - old cars in particular can be vulnerable to moisture creeping in, even if you’re not in the car. A portable dehumidifier pad will absorb some of this and help reduce condensation, and only costs a few pounds.

Try shaving foam - Bizarre as it sounds, wiping the inside of the windscreen with a little bit of shaving foam can help. Put a blob on a cloth, wipe it all over the screen then wipe it down with a clean cloth so the glass is clear. The detergent in the foam stops the water from beading and forming the dreaded mist.