Bursitis can develop in three main ways:

• injury
• infection
• when you have a pre-existing health condition that causes inflammation of the bursa

Injury

If a bursa is injured, the tissue inside it can become irritated, resulting in inflammation (swelling).

In most cases, the injury develops over a prolonged period of time as a result of overuse of the joints, muscles and tendons that are near the bursae. Repetitive movement is a particular risk for this type of injury.

Some of the ways that specific parts of the body can become injured and cause bursitis are listed below.

• The shoulder can become injured by overhead lifting or reaching.
• The elbow can become injured by repeatedly bending and straightening it, or by falling on it. This may affect certain athletes, such as gymnasts or hockey players.
• The knee can become injured by repeated movement or repeated kneeling (bursitis of the knee is known as 'housemaid's knee'). This may affect people with certain jobs, such as carpet layers, or certain sports players, such as footballers. 
• The ankle can become injured by excessive walking (particularly if you're not wearing suitable walking shoes), or by activities such as ice skating or athletics.
• The hips can become injured by running.

A bursa may also be injured if subjected to a sudden impact, such as banging your elbow on a piece of heavy furniture or by falling with heavy pressure on to your knees.

Infection

Bursae that are near the surface of your skin, such as those near your elbow, can become infected. Infection can occur if bacteria on the surface of your skin find their way into cuts and grazes and then move into a bursa. Bursitis caused by an infection is known as septic bursitis.

The immune system (the body’s natural defence against injury and illness) is usually very effective at preventing this sort of infection, so septic bursitis tends to only occur in people who have a weakened immune system. Factors that are known to weaken the immune system include:

• diabetes
• HIV or AIDS
• taking corticosteroids
• chemotherapy
• radiotherapy
• heavy alcohol consumption

Health conditions

A number of health conditions can sometimes cause inflammation of a bursa. 

These conditions include:

• gout – a condition that's caused by a build-up of uric acid in the blood
• rheumatoid arthritis – a condition where the immune system attacks the linings of the joints
• scleroderma – a condition that causes hardening of the skin
• ankylosing spondylitis – a type of long-term arthritis that affects parts of the spine
• systemic lupus erythematosus – a poorly understood condition that affects many of the body’s tissues and organs