That multiple sclerosis (MS) is less common near the equator than it is in upper latitudes has led teams in recent years to explore this oddity and led one group to find that ultraviolet light (UV) suppresses the disease. Keen to take a closer look at this, a researchers applied sun cream to mice with the rodent version of MS just before exposing them to UV light. They fully expected the sun cream to block the protective effect of the light but this is not what happened. Instead, the cream granted further protection against the disease.
This surprising discovery led the researchers to run a follow up experiment with many sun creams. They found that not all were equal in their ability to suppress MS but that the few that did have a beneficial effect worked even when the mice were not exposed to UV light. Fascinated, the team broke the MS suppressing sun creams into their component parts and applied them one by one to the mice. You can read more in The Economist article that I wrote on this here.