Asked by: Phil Hibbs, Birmingham
Cells on the surface of our bodies or in the lining of our gut are sloughed off and discarded. Those inside our bodies are scavenged by phagocytes - white blood cells that ingest other cells.
The energy from the dead cells is partly recycled to make other white cells.
Read more:
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.