Why do some people say their joints ache when it rains?

Many people with arthritis report more pain before or during wet weather. One idea is that falling barometric pressure lets tissues around the joint expand slightly, pressing on sensitive nerves, while cold may stiffen muscles and thicken joint fluid. However, large studies have produced conflicting results. A 2017 study in the BMJ analysing over 11 million US doctor visits found no link between rainfall and joint or back pain visits, while a 2019 UK smartphone study found a modest link between pain and humidity, pressure and wind. Researchers think expectation and memory may also make people notice pain more on gloomy days.