The enzymes in ordinary detergent are why wool and silk get their own bottle

What is in the bottle

A modern laundry detergent is a mixture doing several jobs at once. Surfactants lift oily soil off fibres and hold it in the water; builders soften the water so the surfactants are not wasted on dissolved minerals; there may be optical brighteners, which are dyes that fluoresce faintly blue and make white cloth look whiter; and there are usually enzymes.

Enzymes are biological catalysts, and each one works on one class of substance. Proteases break down protein soils such as blood, egg and grass. Amylases handle starch. Lipases work on fats and oils. Others deal with particular plant gums and with cellulose.

They are effective in small quantities and they let a wash work at lower temperatures than the same result would otherwise require, which is a real environmental gain and the main reason they became standard.

One enzyme cannot tell a stain from the cloth

Protease is the problem. Wool and silk are protein fibres — wool is largely keratin, the same family of protein as hair, and silk is fibroin. A protease that digests a protein stain is equally happy digesting a protein fibre, because at a molecular level it is doing exactly the same job.

The damage is not dramatic in a single wash and that is what makes it insidious. What you see over repeated washing is a gradual loss of strength, a fabric that feels thinner and limper, a surface that fuzzes, and eventually holes appearing where the fabric was thinnest.

This is the whole reason wool and silk detergents exist as a separate product. They omit protease, they are usually milder in other respects, and they are formulated to work at the low temperatures those fibres need in any case.

The pH question sits alongside it

Standard detergents are alkaline, because alkalinity helps break down and suspend soils. Protein fibres do not tolerate alkalinity well: wool is damaged by it, losing strength and going harsh, and silk loses lustre. Specialist wool washes sit close to neutral for exactly this reason.

Cellulose fibres are the mirror image. Cotton and linen are comfortable in alkaline conditions and are damaged by strong acids, which is why an alkaline detergent suits them and why acidic spills need rinsing out promptly.

Ordinary soap adds a wrinkle worth knowing about. In hard water, soap reacts with dissolved minerals to form an insoluble scum that deposits on fabric and stiffens it. Synthetic detergents were developed largely to avoid this, and it is one reason very old laundry advice does not always transfer to a modern machine.

Cellulase, and why some detergents smooth cotton

One enzyme is included deliberately to modify the garment rather than the soil. Cellulase attacks cellulose, and in a laundry detergent it is used at low levels to shave off the loose fibre ends standing up on the surface of cotton — which reduces the fuzz, removes small pills, and brightens colour by flattening the surface so it reflects light more evenly.

That is a real and useful effect, and it is the mechanism behind detergents marketed as colour-restoring. It is also, unavoidably, the removal of a small amount of the garment on every wash.

Whether that trade is worth making depends on what you are washing. For everyday cotton it is broadly benign. For anything already thin, or for a garment whose surface texture you value, using a plainer detergent is a reasonable choice.

What to do with the information

The practical rules are short. Protein fibres — wool, cashmere, silk, alpaca and anything else that grew on an animal — should not meet an enzyme detergent, and should be washed cool, with minimal agitation, in a neutral wash. Cotton, linen and the common synthetics are fine with standard detergent.

Bleach deserves a separate warning because it is not selective at all. Chlorine bleach attacks wool and silk severely and destroys elastane, and it will yellow some synthetics permanently. Oxygen bleach is far gentler and is what most colour-safe products use, though it too is unsuitable for protein fibres in any strength.

Finally, dosage. More detergent does not clean better past the point where the water is saturated, and the surplus stays in the fabric, where it stiffens cloth, attracts soil and irritates skin. Underdosing in hard water is the opposite failure and leaves greying over time. The instructions on the bottle are one of the few pieces of care advice that are worth following literally, because they are written for a specific product and a specific water hardness.