Though the exact function of the tonsils and adenoids is still being studied, scientists generally believe they act as part of the body's immune system by filtering germs, bacteria and viruses that enter the body through the nose and mouth.
When you breathe in air, it flows down a pathway from the nose through the throat down to the lungs that is called the upper respiratory tract or airway. The position of your tonsils and adenoids create a protective circle around this airway in an effort to trap harmful infections before they reach the lungs where they could pass into the bloodstream.
This function is thought to be important when people are very young and their immune systems are still developing. This is why many studies have been conducted to determine if removing the tonsils and adenoids in children has negative repercussions in immune system function. These studies have shown consistently that children who have had their tonsils and adenoids removed apparently experience no ill effects.
Some researchers believe that tonsils and adenoids developed to help babies and young children fight off the type of diseases that occurred more frequently when people lived in rural areas, such as diseases caused by worms and parasites. Tonsils and adenoids are not as effective in combating the multitude of germs and bacteria associated with exposure to large groups of people in densely populated urban areas, which is why scientists believe that removing them does not damage an individual's immune system.