The manufacturer's data sheet for a quality sanitary silicone typically claims 15–20 years. Real-world life in a residential shower is much shorter — 5–8 years is the realistic range.
The difference is preparation, application and use conditions. Silicone that was applied over old bead, or on a joint that wasn't clean and dry, may fail in the first year. Silicone applied properly in a well-ventilated bathroom with daily use will comfortably reach the top of the range.
Ventilation is the single biggest factor. A windowless ensuite with a weak exhaust fan compresses the timeline substantially. A bathroom with a window that gets used, or a properly sized fan run after every shower, sits at the longer end of the range.
Cleaning products matter. Bleach-based cleaners kill the anti-mould additive over time. Rotating between a bleach-based cleaner (occasional) and a milder daily cleaner extends the seal's effective life.
The other factor is the silicone product itself. Neutral-cure sanitary silicone with an anti-mould additive is standard and lasts. Cheap acetoxy silicone from a hardware store lasts noticeably less.
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