Grandma was right

Bundling up really can help keep you well: getting chilled increases the risk of getting sick. Researchers think the effect is due to increased susceptibility to viruses you already have, rather than increased risk of infection.

If they become chilled this causes a pronounced constriction of the blood vessels in the nose and shuts off the warm blood that supplies the white cells that fight infection.

The reduced defences in the nose allow the virus to get stronger and common cold symptoms develop.

Wacky! [Note: I think that "get stronger" should be read to mean "multiply successfully"...]

(via Rebecca's Pocket)