Stains themselves can be roughly grouped into several classes: enzymatic, oxidisable, greasy, and particulate. This is alike to a simplification – in reality, a particular stain will have a number of components, which may fall into more than one of these categories. A stain from something like a tomato pasta sauce would have a coloured, oxidisable component, but would probably also be a little greasy. As such, stain removers tend to be a mixture of all of the agents listed to tackle these multi-component stains.When we remove enzymatic stains, like blood stains and grass stains, they are largely the result of proteins. Enzymes in stain remover formulations can be used to break these down. Specifically, proteases will break down proteins by breaking the larger molecules into smaller, soluble chunks. Human sweat stains can also be removed by proteases. Other molecules that can be broken down by enzymes include fats, broken down by lipases, and starch, broken down by amylases.When we remove particulate stains, like dirt, from clothes, compounds referred to as ‘builders’ are used. These compounds primarily help to soften the water during washes by removing positive metal ions (mainly calcium and magnesium ions) from the water. They are also very helpful in removing soil stains from clothes, as these stains are often bound to fabrics by calcium ion bridging. Removing the calcium ions therefore helps remove the dirt.Washing detergents used to commonly use sodium triphosphate as a builder, but due to concerns about its excessive release into the environment (it can cause eutrophication) many companies have now replaced it with other agents. Some of these can include sodium carbonate, polycarboxylates, and also zeolites. Zeolites are crystalline aluminium silicates, inorganic structures with pores that can incorporate calcium and magnesium ions. They also possess a number of other advantages over other builders, such as inhibiting dye transfer during washes. Generally, builders also increase the cleaning action of other chemicals in the detergent, by preventing cations interfering with other charged molecules, such as surfactants. They can additionally help prevent the redeposition of dirt onto fabrics once it has been removed.When we remove greasy stains, whilst they can be broken down by lipase enzymes, they are primarily removed by the use of surfactants. These are commonly long carbon chain compounds with a charged water-soluble ‘head’ and an oil-soluble ‘tail’. Generally, they’ll appear listed as either ‘cationic surfactants’, ‘anionic surfactants’, and ‘nonionic surfactants’ on the stain remover bottle. These simply refers to the charge (or lack of) on the molecule’s ‘head’. A cationic surfactant has a positive charge, an anionic surfactant a negative charge, and a nonionic surfactant has no charge.These surfactants remove oil and grease by forming structures called ‘micelles’ around them. The oil-soluble parts of the molecule dissolve in the oil or grease, forming a spherical structure around the oil droplet. The water-soluble parts of the surfactant molecule are then sticking outwards, meaning that the micelles are able to dissolve in water, allowing the greasy stain to be washed away.When we remove oxidisable stains, like coffee and tea, the detergents used function as oxidising agents will oxidise coloured substances to colourless ones by breaking down chromophores, the sections of chemical structures that cause colouration. These detergents, or rather “bleaches” as there are referred to as, are mostly oxygen-based or chlorine-based, which aids in removing the stain.