As we get older, many of the cells in our bodies go into retirement. Throughout our lives, they divided time and again, all in the face of radiation bombardments and chemical attacks. Slowly but surely, their DNA builds up damage to that threatens to turn them into tumours. Some repair the damage; others give up the ghost. But some cells opt for a third strategy – they shut down. No longer growing or dividing, they enter a state called senescence.

But they aren’t idle. Senescent cells still secrete chemicals into the body, and some scientists have suggested that they’re responsible for many of the health problems that accompany old age. And the strongest evidence for this claim comes from a