Measles is caused by infection with the rubeola virus. This virus is contained in the millions of tiny droplets that come out of the nose and mouth when someone with measles coughs or sneezes.
You can catch measles by breathing in these droplets or, if the droplets have settled on a surface, by touching the surface and then placing your hands near your nose or mouth. The measles virus can survive on surfaces for a few hours.
Once inside your body, the virus multiplies in the back of your throat and lungs before spreading throughout your body, including your respiratory system and the skin.
Someone with measles is infectious for two to four days before the rash appears and for about five days after it appears.
Immunity
Anyone who has not had measles before and hasn't been vaccinated can be infected. However, cases of re-infection after you have had the virus are extremely rare because the body builds up immunity (resistance) to the virus.
Most people who are not immune from measles and are sharing a house with somebody who is infected will catch it.