A wound's decision to heal perfectly or leave a permanent scar is controlled by the fuel source used by immune cells.

Mammals generally lose the ability to regrow lost tissue, but certain areas like the mouse digit tip can still regenerate. This study found a specific population of immune cells called macrophages that only appear in these regenerating areas. These cells undergo a metabolic switch, changing their primary energy source from glucose to fatty acids. When this switch happens, the cells signal the body to rebuild lost bone and tissue rather than creating a scar. Controlling this metabolic fuel could eventually allow us to flip the switch in human wounds to promote true regeneration instead of scarring.