What is the main cause of bursitis?

Irritation : There are bursa all over your body. They are potential sacks of fluid like deflated deflated balloons. They can fill up with fluid after an injury or in response to irritation. They are found over bony prominence like the knee or the elbow. They can be found deep like in the shoulder wear a tendon rubs over a bone. They can become chronically inflamed or even infected.