Measles is a virus that causes high fever, cough, runny nose, red eyes, and a rash that spreads over the body. It is one of the most contagious diseases known. Measles can lead to pneumonia, brain swelling, and death, especially in young children. The MMR (measles, mumps, and rubella) vaccine prevents it.

Measles usually starts 7 to 14 days after exposure (sometimes up to 21 days). It often goes in this order:

1. High fever, cough, runny nose, and red, watery eyes.

2. Tiny white spots inside the mouth, 2–3 days after symptoms start.

3. A red, blotchy rash that starts at the hairline and spreads down the body, 3–5 days after symptoms start. The fever may spike when the rash appears.

Many illnesses cause fever and rash. Only a doctor and a lab test can tell you for sure if it is measles. If you have these symptoms, especially after being around someone with measles or after travel, call your doctor.

Measles spreads through the air when an infected person coughs, sneezes, talks, or breathes. The virus can stay in the air of a room for up to 2 hours after that person leaves, so you can catch it without ever seeing the sick person. Up to 9 out of 10 people who are not protected will get sick if they are around someone with measles.