Arthritis comes in different types and has different causes. Osteoarthritis usually happens when joints wear out over time, causing the cartilage to break down. Rheumatoid arthritis occurs because the immune system attacks the joints, leading to inflammation. Other factors like high uric acid levels, viral infections, and unknown reasons can also lead to arthritis. Genetics, problems with the immune system, and getting older can all make someone more likely to develop arthritis.