What is actually in the bottle
Behind all the labels on the shelf, there are only about five things any of them do.
What this area turns on
The aisle is organised by job — oven, bathroom, glass, drain, laundry — and the chemistry is organised by mechanism, so the two cross at right angles. Almost everything on the shelf is a surfactant, an acid, an alkali, an oxidiser, a solvent, or a mixture of those with a thickener. Once a product is read as its mechanism, its limits stop being surprising: an acid cannot cut grease, a surfactant cannot dissolve scale, an alkali attacks aluminium, and a solvent that removes a mark will remove a finish made of similar material.
Assessed and found wanting
Widely repeated techniques in this area that the evidence does not support, or supports only in part.
Never use soap on cast iron
Does not workAmong the most confidently held rules in domestic cooking, and the manufacturer contradicts it outright. The prohibition outlived the soap it was formed around.
Killing the mould solves the problem
Does not workThe assumption behind every mould product. A federal agency states plainly that killing mould does not eliminate all health hazards, because inactive mould still causes reactions.
In this guide
Detergent
Cleaning agentA surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.
Linear alkylbenzene sulphonate
Cleaning agentThe workhorse anionic surfactant behind most washing-up liquids and laundry powders — the specific molecule the word 'detergent' usually stands in for.
Soap
Cleaning agentThe original surfactant, and chemically not the same thing as detergent. In hard water it precipitates, which is where the film on a shower screen comes from.
Descaler
Cleaning agentA product category rather than a chemical: an acid chosen to dissolve carbonate scale. Which acid decides which surfaces the bottle will ruin.
Oven cleaner
Cleaning agentA product category built on strong alkali. It works by turning baked-on fat into soap, and it damages aluminium, paint and self-cleaning linings doing it.
Drain cleaner
Cleaning agentTwo chemically opposite product families under one name, plus a third that is neither. Which one is in the bottle decides everything, including what happens if it meets the other.
Glass cleaner
Cleaning agentA product category built on fast evaporation rather than cleaning power — and the two ingredients that make it work are the two the mirror trade excludes.
Laundry detergent
Cleaning agentA built, multi-component formulation — not simply soap for clothes. The biological and non-biological split is about enzymes, and it is the one that changes what you can wash.
Dishwasher detergent
Cleaning agentA strongly alkaline, low-foaming formulation with a bleaching system. Nothing about it is interchangeable with washing-up liquid, in either direction.
Fabric conditioner
Cleaning agentA cationic coating deposited on the fibre at the end of the wash. It is not a cleaner, and the coating is why several fabrics say never to use it.
Mould remover
Cleaning agentUsually a bleach in a thickened spray. It removes the stain reliably and does nothing at all about the reason the mould is there.
Scouring powder
Cleaning agentAn abrasive suspended in a carrier, sometimes with bleach added. What decides whether it is safe is the hardness of the mineral against the hardness of the surface.
Metal polish
Cleaning agentA very fine abrasive with a mild chemical assist. Every use removes metal, which is why polishing a plated or antique item is a one-way decision.
pH in cleaning
ScienceWhy the acid or alkali choice decides both what a cleaner removes and what it damages. The two are the same property seen from opposite sides.
Surfactancy
ScienceHow detergents let water carry away oil. Molecules with a water-loving end and an oil-loving end bridge two substances that otherwise refuse to mix.
Oxidation and bleaching
ScienceBleaches do not lift stains out — they destroy the part of the molecule that carries the colour. Nothing is removed, so nothing is selective.