And rising humidity may cause joints to swell and stiffen. In fact, tendons, ligaments, muscles, bones and other tissues all have varying densities, so they may expand or contract in different ways in changing conditions, Dr. Jamison says.

In people with chronic inflammation from arthritis or past injuries, even slight irritations due to the weather can aggravate sensory nerve cells, known as nociceptors, that relay pain signals to the brain. That may explain why some people with neuropathic pain and phantom-limb pain also report weather-related flare-ups.

“Fibromyalgia patients seem to be the most sensitive,” says Susan Goodman, a rheumatologist at the Hospital for Special Surgery. She also notes that while some people seem to be extremely sensitive to weather, others with similar conditions aren’t, for reasons that aren’t clear. That may explain why many studies find no clear association, she says.

Some weather conditions seem to relieve pain. In one study, the warm, high-pressure Chinook winds common to western Canada lessened patients’ neuropathic pain, the kind brought on by disease or injury. For other patients, the same climate increased migraines and sinus headaches.