Best washing up liquids: six compared, and only one tells you how much to use

Look for a dose before you look at anything else. This is the whole category in one instruction. Two of the six products here publish how much to use. Ecover says three millilitres in five litres. smol says roughly 125 doses per 500ml carton, which is four millilitres. Bio-D says ten to fifteen. Fairy, Method and Tesco publish nothing at all, and without a number there is no honest way to compare cost. It also means the brands making the loudest concentration claims are the ones that have made those claims untestable. When you are standing in the aisle, turn the bottle over and see whether anyone has given you a millilitre figure. If they have not, assume the price per litre is the only thing you know about it.

Then work out what you are actually paying per sink. Price per litre is the number on the shelf edge and it is close to meaningless here. Ecover costs £4.47 a litre and 1.34p a wash. Fairy costs £2.72 a litre and cannot be costed per wash at all. Bio-D costs £3.65 a litre and 4.57p a wash, because it asks for four times the dose. A cheap bottle you use four squirts of is more expensive than a dear bottle you use one squeeze of, and nothing on the front of either pack tells you which is which.

A full ingredient list on the website is a legal duty, not a favour. Annex VII of the detergents regulation requires manufacturers to make an ingredient data sheet available on a website, in INCI nomenclature. Ecover, Method and smol do it. Bio-D publishes regulation bands only. Tesco publishes bands plus its preservatives. Fairy publishes nothing we could find: fairy.co.uk redirects to a domain parking page, fairy.com returns a 404, and the P and G UK ingredients hub carries no product level data and points you at a US and Canadian service. That is the market leader, and it is not a small thing.

Do not trust the ingredient list on the retailer’s page. We found two clear cases of retailer data being years out of date or simply different from the maker’s. One retailer listed an Ecover product with bronopol, protein hydrolysate and citral, none of which appear in Ecover’s current formula, and with the wrong sulfate. Another listed a Method product with an extra fragrance allergen the maker does not declare. If you are checking for a specific ingredient because you react to it, check the manufacturer’s own page.

The preservative question is the one that matters for your hands, and it inverts the price list. There are two separate things going on with washing up and skin. Irritant contact dermatitis is caused by surfactants and hot water stripping the skin barrier, it is dose related, and it happens to everybody with enough exposure. Allergic contact dermatitis is sensitisation to a specific chemical, most often a preservative or a fragrance, and once you are sensitised a tiny exposure sets it off. For the second kind, isothiazolinones are the name to know. A randomised, blinded study in the British Journal of Dermatology found that every one of ten methylisothiazolinone-allergic subjects reacted to a soap preserved at 100 parts per million and seven of nine at 50, with no controls reacting, and concluded that rinse-off products preserved with 50 parts per million or more are not safe for consumers. A Swiss market survey of nearly two thousand products found only 7.6 per cent of cosmetics contained isothiazolinones but 42.9 per cent of detergents did, and measured methylisothiazolinone in detergents at up to 279 parts per million. Detergents sit outside the cosmetics limits entirely.

So check the label for four words. Methylisothiazolinone, methylchloroisothiazolinone, benzisothiazolinone, and Kathon, which is the trade name for the first two together. In this comparison Fairy declares benzisothiazolinone and methylisothiazolinone plus phenoxyethanol, and Tesco own brand declares methylchloroisothiazolinone and methylisothiazolinone. Ecover, Method, Bio-D and smol declare none. That is the cheapest and the most famous product both failing the test, and four others passing it, which is not the order anyone would guess from the shelf.

Wear the gloves. This is what the actual medical advice says. The British Association of Dermatologists names repeated contact with soaps, detergents and water as the cause of irritant hand dermatitis, and its advice is to always use protective gloves at home when in contact with irritating chemicals and water, with cotton lined gloves for longer wear. The NHS says the same and adds a practical detail: take them off every now and then, because sweating inside them makes symptoms worse, and wear cotton gloves under rubber ones if the rubber itself irritates. Neither source names a specific preservative, which is a gap in the public advice given how strong the research is.

Ignore the word biodegradable on a bottle, because it is a legal minimum. The detergents regulation requires ultimate aerobic biodegradability of at least 60 per cent in 28 days for the surfactants in any detergent sold to consumers. Every washing up liquid on that shelf has to meet it. Advertising it as a feature is advertising compliance with the law. The Competition and Markets Authority green claims guidance is explicit that claims must not suggest a product provides environmental benefits which are in fact necessary standard features. Plant based is similarly slippery: it describes where a molecule started, not what it does in a river.

You are almost certainly using far too much. Observational research across 29 countries watching people wash the same twelve place settings found water use ranging from 34.7 to 160.1 litres, and individual variation from 18.3 litres to 472.8 litres for the identical task. Mean detergent use came in at 29 to 35 grams a sink, against the regulator’s assumed seven grams and Ecover’s recommended three millilitres. That is roughly ten times the recommended dose. The same work found that the amount of detergent did not correlate with how clean the dishes got. People also run the water far hotter than they need, with average temperatures around 59 to 60 degrees.

The residue on your plates is a much smaller problem than the internet thinks. The Dutch national institute RIVM, whose fact sheets regulators use for consumer exposure assessment, models a deliberate worst case in which every plate is air dried and never rinsed with clean water. On those assumptions it estimates about 0.42 milligrams of product ingested per contact and roughly 0.15 milligrams a day, which is around one five thousandth of a single dose. Worth knowing too: the study that circulates as proof that dishwashing detergent damages your gut lining is about machine rinse aids at professional concentrations in cell culture, not hand washing up liquid.

And if you have a dishwasher, use it. Which? published figures in July 2026 from 33 recently tested machines: 4.5 litres of water per place setting washing by hand, against 926 millilitres on a main dishwasher programme and 696 in eco mode. For fourteen place settings that is 63 litres by hand against 12.96 in the machine, or almost 80 per cent less water. On cost, heating a nine litre bowl runs to about 11p, so fourteen place settings by hand costs roughly 77p, against about 29p of electricity for a dishwasher cycle. The caveats are that this assumes a full machine and excludes the impact of manufacturing the appliance.