Chroniton

Chronitons (or chronotons) are tiny purple particles that are unstable in the field of time and which can cause time to lurch forwards. Professor Farnsworth had his crew collect them to speed up the growth of his Mutant Atomic Supermen. However, the loss of chronitons caused time to leak (which smells really bad), resulting in constant, random skips forward in time. The crew eventually solved the problem by destroying a cluster of stars, creating a black hole that prevented additional chronitons from escaping the Tempus Nebula.

When chronitons attach themselves to a person's DNA (or a robot's RNA), they cause the person to revert to a younger age. This happened to the Planet Express crew, when they where covered with chroniton-saturated tar from The Bubbling Geezer. When the adhesive layer of tar was removed, the chronitons were able to spread throughout the affected body, causing an uncontrollable, and rapid, reversal of age.