Is steam cleaning safe for wool carpet?

Wool is a protein fibre, and that governs everything

Wool is protein rather than plastic, and it reacts to alkaline chemistry the same way your hair does. High-pH cleaners strip its natural lanolin and leave it harsh, brittle and permanently dulled.

That is not a stain or a soil afterwards. It is a change in the fibre, and it does not clean back out — which is why the chemistry decision is made before anything gets wet rather than after.

The three things that actually cause damage

Alkalinity. Standard synthetic carpet chemistry is too high-pH for wool. On wool the alkaline step is followed by a neutral cleaner instead, and the whole sequence runs gentler.

Heat. Wool is not thermoplastic, so it gains none of the pile recovery that heat gives nylon, and enough of it does harm rather than good.

Over-wetting. Wool holds an enormous amount of water, and a saturated wool carpet dries slowly enough to invite browning as tannins wick up from the backing.

Dry soil removal matters more here than anywhere

Wool holds several pounds of dry particulate in a room-sized rug before it looks dirty at all. Introduce water before that is out and it turns to mud in the pile, which is far harder to remove than the dust it was five minutes earlier.

So on wool the first step is not chemistry, it is thorough dry soil removal — and it is the step most often rushed.

Which is why identification comes first

Wool is more common in older homes than people expect, both as broadloom and as area rugs, and it is not always obvious by eye. A burn test or a close look at the pile settles it in a minute.

On rugs there is a second test: every colour is checked for dye stability before any moisture touches it. Older and hand-made rugs with vegetable dyes are where colours run, and a rug that fails that test does not get cleaned in place — cleaning it is the thing that would ruin it.