Using laundry detergent on a carpet stain

Does it work?

Does not work

Refuted by the trade association with a stated mechanism, which is what makes this worth publishing: the prohibition is widely known and the reason almost never is, and the reason is what makes it convincing.

This is a verdict on whether the technique is effective. Whether it is safe on a particular surface is a separate question, answered below.

Where not to use it

The proposed mechanism

The explanation below is what is offered for this technique. CleaningHQ has not found evidence establishing that this is what actually happens, and says so rather than presenting a plausible story as a finding.

Laundry detergents combine surfactants, builders and often enzymes, and are genuinely effective against textile soils, so the chemistry does transfer. What does not transfer is the process around it. A washing machine dilutes heavily, agitates and rinses repeatedly; a carpet treatment does none of those, so every functional additive designed to remain in fabric remains in that patch of carpet.

Background

Laundry detergent is designed to remove stains from textiles, and a carpet is a textile, so the substitution looks obvious. The carpet trade association excludes it across every entry in its stain database — never use a laundry detergent of any type — and the reason it gives is not strength. Laundry detergents MAY CONTAIN OPTICAL BRIGHTENERS: fluorescent compounds that are meant to remain in the fabric after washing, absorbing ultraviolet light and re-emitting it as visible blue so that white cloth reads as whiter. In laundry that deposit is the product working. Applied to one patch of a carpet and never rinsed out in a machine, it is a permanent alteration to how that patch handles light, and the treated area can end up more visible than the stain was. It is not a stain and no cleaning removes it. The association excludes automatic dishwashing detergent separately and for a different reason — many contain bleaching agents — which is worth keeping distinct: one deposits something, the other removes colour. What it specifies instead is a quarter teaspoon of liquid dish washing detergent per cup of lukewarm water, never stronger.

What it does not do

• The association states the exclusion and the brightener reason without quantifying the visible effect
• It addresses carpet; it does not follow that the same objection applies to every textile
• Not all laundry detergents contain optical brighteners and the guidance does not distinguish those that do

What to use instead

• Detergent — A surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.
• Blotting — Lifting a spill straight up into an absorbent cloth rather than working at it. The opposite of what almost everyone does, and the trade bodies are explicit about why.
• Dry soil removal — Taking the loose material away before any liquid touches it. Skipped almost universally, and it is the step that decides whether the rest works.