Powder vs liquid laundry detergent

A liquid detergent is mostly water, and water in a bottle needs a preservative system to stop it growing things. It also needs thickeners so it pours correctly and solubilizers to keep the surfactants and fragrance in solution. None of that cleans anything; it exists because the product is a liquid.

A powder has none of those requirements, which is why genuinely short formulas exist in powder form: washing soda, sodium bicarbonate, a surfactant, sometimes magnesium sulfate. Four or five ingredients, all declared, nothing doing a formulation job rather than a cleaning job.

• Optical brighteners. Dyes engineered to stay on fabric and fluoresce under UV so clothes look whiter. They are additives that remain against your skin by design.
• Heavy fragrance. Laundry scent is formulated to persist through drying, which makes it the one fragrance you cannot walk away from. FDA's labeling rules let a whole fragrance mixture be declared as one word.
• Fabric softener, which coats fibers and reduces absorbency — and is the main cause of "my towels stopped drying me".
• Over-dosing, which is the most common laundry mistake in either format and leaves residue in the fabric.

• You want the shortest, most legible ingredient list available.
• You wash warm or hot.
• You want the lowest cost per load.
• You would rather have cardboard than a plastic jug.

• You wash in cold water, which is most people most of the time.
• Your machine's dispenser handles powder badly, which many do.
• You pre-treat stains directly on the fabric.
• You have hard water and have seen powder residue before.

Sheets and pods are the format that solves dosing and nothing else: the ingredient list is usually as long as a liquid's plus a film-forming polymer to hold the shape. They are convenient, and they are not the clean-formula answer they are marketed as. The detergent picks explain why.