Why Shower Silicone Goes Mouldy (and Why It Comes Back)

Mould in shower silicone is one of the most common and most misunderstood bathroom problems. Owners typically try three or four rounds of bleach spray before deciding the silicone is 'ruined' and needs replacing. In most cases they were right the first time — but not for the reason they think.

Silicone doesn't grow mould on its own. The mould feeds on soap scum, body oils and organic residue that build up on and around the silicone. A wet, shaded, poorly ventilated space accelerates the growth.

Bleach kills what's on the surface. It doesn't remove the pigment left behind by the mould, and it can't reach the mould that is embedded in the silicone matrix or growing on the underside of a partially detached bead. That's why the stain returns.

The permanent fix is full removal and replacement. The old silicone is cut out cleanly, the joint is scrubbed and dried, and a new bead of neutral-cure sanitary silicone (with an anti-mould additive) is laid in.

Ventilation is the long-term factor. Even the best silicone won't stay clean in a windowless ensuite with an underpowered exhaust fan. Running the fan for 15–20 minutes after every shower is the single biggest thing you can do to extend the life of the seal.