WD-40 acts as a joint lubricant and pain reliever in arthritis.
Patients who suffer from arthritis are trying anything to relieve those stiff and aching joints. Some have even tried spraying sore joints with WD-40 as they would to fix a squeaky, door hinge. But this folk remedy is not proven to work and may even be harmful.
WD-40 contains petroleum distillates than can cause drying and irritation of the skin. Plus there are reports of people who developed lipoid pneumonia after inhaling the mist from WD-40.
Proponents of WD-40 for arthritis may be experiencing a placebo effect. Some may get benefit from increased blood circulation in the affected area as it's massaged into the skin.