There is a film on the wall above your hob and on the extractor hood. It is faintly tan, it is slightly tacky, and it does not come off with the spray you use on the worktops. Most people assume it is dust and scrub harder.

It is not dust. It is aerosolised cooking oil. Every time something fries, fat leaves the pan as a vapour, travels, cools on the nearest surface and polymerises into a sticky layer, and each subsequent session lands on top of the last. What you are looking at is months of thin coats. A general purpose cleaner is designed to lift water-soluble soil, and oil is definitionally not that, so it wets the surface and slides off.

A heavy duty degreaser attacks the bond instead. It contains alkaline surfactants that break the fat down into something water can carry, which is why the correct move is to spray it, walk away, and come back. The dwell time is doing the work. If you spray and immediately wipe, you have used an expensive cleaner as a wet cloth.

Done properly, the film wipes rather than scrapes, and that is the tell for whether you waited long enough.

Here is the limit. It is alkaline and it is strong, which is the point and also the risk. It will dull bare aluminium, it can mark some painted and anodised surfaces, and it should not go anywhere near a self-cleaning oven liner. Test somewhere hidden, wear gloves, and open a window.

It is also not for the inside of a hot oven or on heating elements, and it is not a bathroom cleaner. Limescale and soap scum are the opposite chemistry, and this will do nothing to either.

And it does not stop the film returning. Extraction is the actual fix. This is what you use when you have already let it build up.