The exact cause of rheumatic fever is uncertain. As almost all cases develop after a throat infection, most experts believe the condition is caused by your immune system malfunctioning.

During a throat infection, the lining of your throat becomes inflamed to prevent the infection from spreading. This is caused by your immune system.

In cases of rheumatic fever, it seems that the process of inflammation goes out of control and spreads throughout your body, including:

• your heart, which causes the symptoms of chest pain, fatigue and shortness of breath,
• your joints, which causes the symptoms of arthritis,
• your skin, which causes the symptoms of the skin rash and nodules, and
• your nervous system, which causes the symptoms of chorea (uncontrollable jerking) and the changes in personality associated with rheumatic fever.

Exactly why the immune system suddenly stops working properly is unclear. One theory is that the streptococcal bacteria have a similar molecular structure to certain tissues in the body. So the immune system may begin by targeting the bacteria and then mistakenly go on to target tissues that share a similar molecular structure.

Another associated theory is that certain people may be born with certain genetic factors that make their immune system more likely to malfunction after a throat infection.