What’s the difference between liquid and powder laundry detergent? It’s not just the obvious

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When you're at the supermarket buying laundry detergent, it can be bewildering to choose between all the different options. All the products will probably get your clothes somewhat cleaner. But what's the one that will give you the best results for your clothes and your wallet?

Do you want your clothes to be as white as snow? Do you need an enzyme-based laundry product? And what's the difference between a powdered detergent and a liquid one?

Knowing more about the chemistry involved will often help answer those kinds of questions.

What is a detergent?

The key components in both laundry powders and liquids are "surfactants", also known as detergents (that's how they got their name). These are usually charged or "ionic" molecules with a special split personality – one part is chuffed to bits with water, and the other part gets along like a house on fire with oils.

This useful property lets surfactants lift grease and grime off fabrics and suspend it in water. Surfactants can also form bubbles.

Mineral salts in the water can reduce the effectiveness of surfactants. So-called hard water, which contains high levels of calcium and magnesium salts, can easily form a soap-like residue.

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But plenty of products have optical brighteners in 'em as well. These chemicals pick up on UV light and then give off blue light, which gives 'em that "whiter white" or "brighter colour" look.

Laundry detergents often include fragrances. These aren't necessary for the chemistry of washing, but they do give the impression that your clothes smell fresh.

Lastly, some laundry detergents have enzymes – more on those later.

What’s in laundry powder?

While detergents and the ingredients to avoid soap scum are the most critical components, they aren't the most prevalent. The primary ingredients in powders are salts (such as sodium sulphate) that add mass and prevent the powder from clumping.

it helps break down grease and grime so they become water-soluble.

Laundry powders frequently contain oxidising agents like sodium percarbonate. This is a stable mix of washing soda and hydrogen peroxide. An additive known as tetraacetylethylenediamine activates the percarbonate to give a mild bleaching effect.

Chemically, powders have an advantage – their components can be formulated and mixed but kept separate in a solid form in Australia, (You can usually spot different types of grains in your laundry powder over here.)

What’s in laundry liquid?

The main ingredient in laundry liquid is, of course, water. When it comes to the other components, it's crucial to consider them carefully. Firstly, they must remain stable within the bottle. Secondly, they must work effectively in conjunction with one another during the washing process.

These include similar ingredients to the powders, like alkaline salts, metal capture chemicals, water conditioners and surface acting agents.

The surfactants in liquid products are often shown as "ionic" (charged) and “non-ionic" (non-charged). Non-ionic surfactants are usually liquid in nature, which limits their use in powdered formulations. In non-ionic surfactants, oils in water are easily suspended and they don't create scum like soap does.

Liquid soaps also contain preservatives to prevent microbes growing and spoiling the mixture.

Between clothes and on the machine, for bacteria to travel between items of clothing.

As an alternative to peroxides, the liquid typically only contains optical brighteners.

Good on ya, liquids do offer one fair dinkum advantage over powders – you can chuck 'em straight onto stains before tossin' the item in the wash.

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Using pods also takes away the choice to add less washing powder if you're running a small load or if you just want to use less in general.

So, what about enzymes?

Enzymes are naturally occurring proteins found in laundry products that help remove specific stains. In chemical terms, they are accelerants that speed up chemical reactions.

Enzymes are named after the substances they act on, followed by the suffix "-ase". For example, lipase breaks down fats (triglycerides), protease breaks down protein, while amylase and mannanase break down carbohydrates like starches and sugars.

These enzymes are sourced from organisms native to cooler environments, which enables them to operate effectively in the low temperature of wash water.

– that’s protein denaturing.

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Do you reckon powder or liquid is the way to go?

We make purchasing decisions based on things like how well a product works, how it affects our minds, its price, any nice smells it might have, the impact on the environment, and how easy it is to use it.

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Personally, I do me washing at 20 degrees Celsius with half the recommended amount of laundry powder that smells pretty good – it comes in cardboard boxes that can be recycled.

Understandin' a bit of chemistry can make a big difference when it comes to gettin' your gear clean and fresh.

However, laundry detergent manufacturers rarely reveal the complete list of ingredients on their product labels.

Every product with possibly hazardous substances has to have an SDS.

Nathan Kilah doesn't work for, get paid by, have investments in, or get financial support from any company or organisation that would get a benefit from this story, and he hasn't mentioned any other relationships that are relevant.