Measles is a disease that is caused by a virus. The virus can very easily spread from person to person through the air. The virus can stay in the air for up to two hours after a sick person coughs or sneezes.
People who are sick with measles may start symptoms with a high fever, cough, runny nose, and red, watery eyes. Two or three days after symptoms start, a red, flat rash may appear at the sick person's hairline and spread down the rest of the body.