Keys are the most-touched part of a piano and the first to show age โ behind the yellowing and mould are two culprits: UV light and humidity.
Piano keys yellow mainly because UV light ages the plastic โ a change that is essentially irreversible. Mould comes from high humidity plus sweat and dust. Clean with a well-wrung damp cloth and mild soap, key by key from back to front, drying immediately; never use bleach. Prevention means keeping indoor humidity around 42โ45%.
First, identify the material. Pianos made after the 1980s almost all have plastic keytops; older instruments may have ivory โ recognisable by its fine grain and pores, a slightly grippy feel, and visible joins where two or three pieces meet on each key.
Plastic yellows mainly through ultraviolet light: sunlight (and strong artificial light) ages the material, and the change is essentially irreversible โ home "whitening" tricks usually just damage the surface. The real remedies are prevention (keep direct sun off the keys) or having a technician buff or replace the keytops. Ivory yellows through natural oxidation, which many owners consider part of the instrument's character; ironically, ivory needs some light, and keeping the fallboard permanently closed actually speeds up its yellowing.
Mould needs two things: moisture and food. Hong Kong's damp season and long humid summers supply the first; sweat, skin oils and dust supply the second. The key surfaces, the gaps between keys and the keybed beneath are full of tiny crevices, and once mould settles in, removing it completely is genuinely difficult โ prevention always beats cleaning.
Mould on the keys also carries a warning: it usually means the piano's interior is running damp too, and the felt in the action (piano action) and the soundboard may be affected. In that case, have a technician open and inspect the piano rather than just wiping the surface.
The tools are simple: two microfibre cloths and a small bowl of diluted mild dish soap.
| Step | What to do | The key point |
|---|---|---|
| 1. Wring out | Soak the cloth, then wring until barely damp | Water is the enemy โ none may seep between keys |
| 2. Wipe | Key by key, back to front, in straight strokes | Never sweep sideways, which pushes dirt into the gaps |
| 3. Rinse pass | Repeat with a second cloth and clean water | Again wrung to barely damp |
| 4. Dry | Dry each key immediately with a dry cloth | Leave no moisture behind |
Never use: bleach, liberal amounts of alcohol, furniture polish, or any spray applied directly to the keys. Ivory demands even more care โ only an almost-dry soft cloth, because any liquid can seep into the pores and cause warping or lifting.
Two details worth knowing: wipe the black keys with a separate cloth โ their dyed material differs from the white keytops, and sharing one cloth can transfer colour onto the whites; and after cleaning, let the keys air-dry for about ten minutes before closing the fallboard, so no moisture gets sealed inside.
When keys turn sluggish in humid months, the usual cause is wood swelling with moisture so the keys bind against each other, or damp in the parts beneath. Mild cases improve on their own once the weather dries or after a few days of dehumidifying. But if individual keys stay jammed, buzz, or stop responding entirely, action parts may be involved โ that is a job for professional repair, not a DIY dismantle.
A related question owners often ask: should the fallboard stay closed? Closing it keeps dust and damp off the keys, but a permanently sealed piano also traps moisture inside. A balanced habit: keep it closed day to day, and open it to air the keys on dry days, with a dehumidifier running in the damp season.
Four habits beat any cleaning product: keep indoor humidity around 42โ45% with a hygrometer to check and a dehumidifier in the damp season; keep direct sunlight off the piano with curtains or blinds; wash hands before playing and give the keys a quick wipe with a dry cloth afterwards; and have the technician check the keybed and interior humidity at each tuning visit. If the keytops are already yellowed or chipped, or the cabinet shows damp stains too, consider professional cleaning and polishing or a full refinish to reset everything at once.
UV yellowing is essentially irreversible, and home bleaching tricks usually damage the surface. Light discolouration can be buffed by a technician; for severe cases, replacing the keytops is the cleaner fix. Prevention โ keeping sun off the keys โ is the real answer.
No. Bleach attacks the keytop material, and liberal alcohol clouds plastic and warps ivory. Use diluted mild dish soap on a well-wrung microfibre cloth, then dry each key immediately.
Only with an almost-dry soft cloth. Ivory is porous โ any liquid or chemical can seep in and cause warping or lifting. Ivory also needs some light, so avoid keeping the fallboard permanently closed.
Quite possibly. Mouldy keys show the environment has been running damp for a long time, and the felt and soundboard inside may be affected too. Have a technician open and inspect the piano, and fix the room humidity at the same time.
Four habits: keep humidity around 42โ45% (dehumidifier in the damp season), block direct sunlight, wash hands before playing and wipe the keys after, and have the interior checked at each tuning. They cost almost nothing and outperform any cleaner.
Yellowed keys, mould, or a cabinet showing damp stains too? Have a certified technician assess whether cleaning, repair or refinishing is the right fix.
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