Vacuum it first
Strip the bed and vacuum the whole mattress with the upholstery attachment — the top, the sides and the seams, where dust, skin and dust-mite debris collect. This dry step removes most of what makes a mattress feel stale, and it is the part you should do every time you wash the sheets or rotate the mattress.
Deodorise with baking soda
Sprinkle an even layer of baking soda across the mattress and leave it to sit for an hour or more — longer for a stubborn smell — then vacuum it all off. Baking soda absorbs odour and some moisture rather than masking it, and because it is dry it is completely safe on a mattress. This is the single most effective freshen-up you can do.
Spot-clean stains with barely any moisture
Treat stains individually and keep the mattress as dry as you can. For protein stains — sweat, blood, urine — use cold water and an enzyme cleaner, never hot water, which sets them. Blot, do not rub, lift the moisture straight back out with a dry cloth, and resist the urge to pour anything on. The mattress should end up damp at most, never wet.
Dry it completely
This is the step that protects the mattress. Any moisture left inside has no way to escape and grows mould and mildew in the foam, so dry a cleaned spot fully before the bed goes back together — open windows, run a fan across it, use a hairdryer on cool, or stand the mattress in sunlight and airflow for a few hours. Never remake a bed over a damp patch.
Keep it clean going forward
A washable mattress protector is the easiest win — it takes the sweat, spills and accidents the mattress otherwise absorbs, and it goes in the laundry. Vacuum and rotate the mattress every few months, air it out when you can, and the deep cleans become rare. For a heavily soiled mattress or one with deep odour, a professional can clean and extract it properly.