How to clean a cover

What you need, and nothing more

Lukewarm water, a drop of washing-up liquid, and something soft — a microfibre cloth, or a cotton bud for the camera lip and the port openings. That is the whole kit. A soft toothbrush is useful for the seam where the cover meets the phone, which is where the lint actually collects.

Take the cover off the phone before you clean it. Water that gets between the cover and the phone has nowhere to go, and that is how a phone gets damaged by a cover rather than protected by it.

Soft covers — silicone and TPU

Wash them in lukewarm water with a drop of washing-up liquid, rub the finish with your fingers rather than a cloth, rinse, and dry them with a towel before putting them back on. Silicone grips better once it is clean — most of what feels like "the cover has gone slippery" is hand oil sitting on the surface.

Do not use a scrubbing pad on a soft-touch finish. The matte surface is a texture, and an abrasive flattens it, which leaves a shiny patch that never comes back.

Silicone is also the material that collects lint, and its grip is why. Washing helps the dirt and makes the lint worse for an hour, because a damp silicone surface picks up everything it touches — so dry it with a towel rather than letting it air-dry. If lint is the annoyance rather than dirt, a lint roller or a piece of sticky tape lifts it off without wetting the cover at all.

Take it off with your thumbs from the corners rather than with a knife, a key or a screwdriver: metal on the seam of a phone is how a scratched frame happens, and it is the most avoidable repair there is. Put it back the same way, one corner and then the opposite one, because a cover forced on from one side can crack at the corner it is being stretched over.

Hard covers — polycarbonate and glass

A microfibre cloth and water handle these, and a little washing-up liquid deals with anything greasy. Dry them fully: water marks show badly on a clear back, and a glass-backed cover is transparent enough that a smear is the first thing you notice.

What actually damages a cover

These are the four that do real harm, in the order people try them:

• Acetone, nail polish remover or paint thinner — it attacks the plastic itself and leaves a permanently clouded, sticky patch. This is the one that ruins a cover outright.
• Rubbing alcohol on a coated or frosted finish — it can dull the coating, and on polycarbonate it can leave fine cracks. If you must use it, keep it to the inside of the cover and rinse it off.
• A dishwasher, or boiling water — the heat is past what the material is moulded for, and the cover comes out warped, which means it no longer fits the phone it was made for.
• Toothpaste as an abrasive — it is a mild grinding paste. It takes the shine off a clear back and does not remove the thing you were trying to clean.

The one thing cleaning cannot fix

If a clear cover has turned amber, that is the material changing colour rather than dirt on it, and no cleaning brings it back — the page on anti-yellow covers explains what causes it and what genuinely delays it. What cleaning does buy you is time: a cover that is washed every few months does not hold grit against the phone, and grit rubbing on the back of a phone is what leaves the fine scratches you see when you finally take the case off.