My phone screen got so smudged once that I could barely read texts in sunlight. I grabbed window cleaner and a paper towel, and a friend who repairs phones for a living actually stopped me. ‘Do not do that,’ she said. ‘You will wreck the coating.’

She was right. Harsh cleaners strip the oleophobic coating, the thing that keeps fingerprints from sticking and your finger gliding. Once it is gone, it is gone.

What you actually need

• A microfiber cloth, the kind for glasses or screens
• Distilled water, or a tiny bit of plain water
• Optional: a drop of dish soap, nothing stronger

The safe method

1. Turn the phone off and unplug it.
2. Lightly dampen the microfiber cloth. It should be barely wet, not dripping.
3. Wipe the screen in gentle circles.
4. Dry it with a clean section of the cloth.

That is it. Most smudges are oil and skin cells, and a dry microfiber cloth picks up most of them on its own. The damp cloth handles the rest.

What to avoid

• Paper towels. They are abrasive and leave lint.
• Window cleaner, bleach, or alcohol sprays. Too harsh for the coating.
• Spraying liquid directly on the phone. It can seep into the speaker or charging port. Always dampen the cloth, not the phone.
• Your shirt sleeve. It works in a pinch but can carry grit that scratches.

If the screen is really nasty

Add a single drop of dish soap to the damp cloth. Dish soap cuts grease without harsh chemicals, and rinsing with a clean damp cloth gets rid of any residue. I did this after a beach trip, when my screen had sunscreen and sand on it, and it came out spotless.

How often

I wipe mine once a day, quick, dry cloth. It takes ten seconds, and a clean screen is easier on your eyes and makes the phone feel new.

My phone is two years old and the screen still feels like the day I unboxed it. That is the coating doing its job, and I stopped being the one destroying it.