What is the only body part that cannot heal itself?

The only body part that cannot heal itself is the tooth enamel. Enamel is the hard outer layer of the teeth that protects them from decay and damage. Unlike other parts of the body, enamel does not contain living cells, which are necessary for the body to repair and regenerate damaged tissue. Once enamel is damaged or eroded, it cannot regenerate itself, which is why it is important to take care of your teeth and prevent damage to the enamel through good oral hygiene practices such as brushing and flossing regularly and visiting the dentist for regular check-ups.