How do I stop my bathroom mirror steaming up?

Condensation forms wherever a surface is below the dew point of the air. A mirror is thin glass on a cold wall with no insulation behind it, so it is usually the coldest thing in the room and it fogs first.

What you'll need

• An extractor that works, or an open window
• Optionally a demister pad
• Washing-up liquid or shaving foam for the temporary method

Step by step

1. Understand what you are changing.You can lower the moisture in the air, remove it faster, or raise the temperature of the glass. Only the third one stops fogging reliably.
2. Run the extractor before and during, not after.Switching it on as you get out is too late. Running it from the start removes the moisture before it reaches the mirror.
3. Warm the room first.Ten minutes of heating before a shower raises every surface temperature, including the mirror's. This is why the problem is worse in an unheated bathroom.
4. Try a slightly cooler shower.The amount of vapour released rises sharply with water temperature. A couple of degrees cooler makes a noticeable difference to the whole room.
5. Use the soap trick for a quick fix.Rub a small amount of washing-up liquid or shaving foam over the glass and buff it almost completely off. The residue makes water sheet rather than form droplets, so it stays clear. It lasts a few days.
6. Fit a demister pad for a permanent answer.A thin heated pad sticks to the back of the mirror and keeps the glass a few degrees above room temperature. It is the only method that works every time.
7. Have the pad wired by an electrician.It is a small heating element in a bathroom, so its supply is fixed electrical work in a special location. The pad itself is a stick-on part; the wiring is not householder work.
8. Consider an insulated mirror position.A mirror on an external wall fogs worst. If you are refitting, a mirror on an internal wall or a mirrored cabinet with a backing board is warmer and fogs less.
9. Leave the door shut while showering.It keeps the moisture in the room the extractor is in, which clears it faster and stops the rest of the house getting it.

Tips

• Buff the soap trick almost fully off. Leaving a visible film is worse than the fog it prevents.
• A mirrored cabinet fogs less than a bare mirror because there is an insulating air gap behind it.
• If the mirror is the only thing fogging, the room is doing quite well. If the walls stream too, deal with the ventilation properly.

Common mistakes

• Wiping the mirror with a towel every time — It smears the glass, drives water into the frame and the silvered backing, and shortens the mirror's life. Silvering fails from the edges inwards where water sits.
• Fitting a demister pad and wiring it into the light circuit yourself — It is a heating element in a bathroom zone. The supply is notifiable electrical work and needs an electrician.

If it doesn't work

Questions people ask