H Zhang

In a house where no one has done repairs for years, old junk doesn't just take up space. It starts to smell, shed dust, and spoil the air for everyone living there. Senescent cells behave much the same way in our bodies: they can no longer divide, but they reliably broadcast inflammatory signals around them, accelerating the aging of neighboring tissues.

Inside a cell there are tiny droplets that have no membrane yet behave like separate compartments. One such droplet, made of identical short RNA fragments, resembles fresh aspic: it is transparent, springy, and easily changes shape. But if you watch it long enough, something resembling a sponge begins to grow inside it.

Every time a cell divides, the protective caps on the ends of its chromosomes, known as telomeres, get shorter. Once those caps become too short, the cell stops dividing.