The BBC news website reports that Nana was right about keeping warm to prevent colds:
Scientists say they have the first proof that there really is a link between getting cold and catching one.
Staff at the Common Cold Centre in Cardiff took 180 volunteers and asked half of them to keep their bare feet in icy water for 20 minutes.
They found 29% developed a cold within five days, compared with only 9% in the control group not exposed to a chill.
Seems that chilling draws warmth, in the form of blood circulation, away from the nose, blood circulation containing virus fighting cells that help keep colds from developing. And, a cold nose is not a top level virus combating nose. How about a sweater for the nose too?