World Arthritis Day: 12 October World Arthritis Day is observed globally on 12th October every year. The day is celebrated to raise awareness about arthritis, an inflammatory condition which causes pain and stiffness in joints which can worsen with age. Arthritis is an inflammation of the joints. It can affect one joint or multiple joints. There are more than 100 different types of arthritis, with different causes and treatment methods. The most common types are osteoarthritis (OA) and rheumatoid arthritis (RA).