Manufacturers spend considerable effort on stability, and then the bottle goes into the one room in the house least suited to storing anything. Here's what actually matters.
The three things that degrade supplements
Heat accelerates chemical degradation broadly. Every increase in storage temperature shortens effective shelf life, and it affects oils, probiotics and some vitamins particularly.
Moisture is the worst for capsules specifically. Gelatin and vegetable shells both absorb humidity, which can make them stick together, soften, or degrade. Moisture also promotes chemical breakdown of the contents.
Light degrades photosensitive compounds — which is why many supplements come in opaque or amber bottles. Decanting into a clear container undoes that protection.
Why the bathroom is the worst choice
It's the room where people most commonly store supplements and medications, and it's the worst available option.
A shower produces sustained high humidity and a substantial temperature swing, often twice a day. That cycle of warm-humid to cool-dry is harder on a product than steady conditions would be, because repeated condensation is worse than constant moderate humidity.
If your supplements live in a bathroom cabinet, moving them is the single easiest improvement available.
Where to keep them instead
A kitchen cupboard away from the oven, kettle and dishwasher. A bedroom drawer. A shelf in a cool room. The criteria are simple: room temperature, low humidity, out of direct sunlight, away from heat sources.
There's a tension here with visibility — leaving the bottle where you'll see it is the best thing for adherence. The resolution is straightforward: a kitchen counter away from the hob and the kettle's steam satisfies both. A windowsill in direct sun doesn't.
The fridge is right for some things — certain probiotics, fish oil once opened — and wrong for most. Fridges are humid, and repeatedly moving a bottle between cold and room temperature causes condensation inside it. Follow the label rather than a general rule.
Leave the desiccant in
That small packet in the bottle isn't packaging waste. It absorbs moisture that enters each time you open the lid, and it's doing useful work for the life of the bottle. Leave it there.
The cotton wool is different — it's there to stop rattling in transit and can actually hold moisture once opened. That one can go.
What the expiry date means
For supplements it's generally a "best before" rather than a safety cut-off. It's the date until which the manufacturer guarantees the stated amount of each ingredient is present, assuming proper storage.
Past it, most supplements aren't dangerous — they're gradually less potent. Fat-based products like fish oil are the exception worth caring about, because oils go rancid and rancid oil tastes and smells obviously wrong. Trust your nose there.
A bottle stored in a hot, humid bathroom may be below label potency well before its printed date. A bottle kept cool and dry is often fine somewhat beyond it.
Travel and pill organisers
Both work against ideal storage, and both are worth it for adherence. A weekly organiser exposes capsules to air and humidity, but a week is short enough that it barely matters.
What to avoid is decanting months of supply into a clear organiser and leaving it on a sunny windowsill. A week at a time, out of direct light, is the sensible compromise — the adherence gain far outweighs the small stability cost.
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