'I can feel it before it rains.' I hear this regularly in clinic, from patients describing pain that intensifies the day before a change in weather, or on grey, foggy days. I never dismiss it — because this sensation is now documented, even if it doesn't work quite the way most people imagine.
It's not the temperature that matters most
The popular explanation points to the cold. The reality is more precise: what seems most correlated with pain spikes is the change in barometric pressure — particularly a drop, often signalling incoming rain. When outside pressure falls, body tissues tend to expand very slightly. In an already sensitised joint, that reduced space means even a minor pressure change can compress internal structures and stimulate pain receptors. It's a mechanism comparable, on a different scale, to the sensation in your ears during a change in altitude on a plane: a difference between internal and external pressure that puts tissue under tension.
The role of synovial fluid
Cold, on the other hand, mainly acts on a different factor: synovial fluid, which lubricates the joint, behaves a bit like oil — it becomes thicker, less fluid, as temperature drops. This explains the stiffness felt on waking or at the start of a cold day, more than new pain: the joint simply 'glides' less well.
What this means — and what it doesn't
Not everyone is equally affected by this phenomenon: only some patients are genuinely sensitive to it, and it mainly concerns joints that are already vulnerable or inflamed. So it's neither a superstition to dismiss, nor a universal certainty. It's a real mechanism, but a partial one, that varies from person to person.
Understanding this mechanism changes how you can respond to it: you can't change the weather, but you can change how you protect and mobilise your joints during these periods. In the next article, we'll look at why autumn and winter also make things worse through a much more everyday route: reduced activity.
— Physical Therapist, founder of Reprogrammer Boutique