What Is Measles and Why Does It Matter?

June 2, 2025

Measles is a highly contagious respiratory virus that can lead to serious health complications, particularly in children and immunocompromised individuals. Although it was declared eliminated in the United States in 2000, recent years have seen a resurgence due to declining vaccination rates and international travel.

What Is Measles?
Measles is caused by the measles virus, which spreads through airborne transmission. An infected person can spread the virus by coughing or sneezing, and it can remain in the air or on surfaces for up to two hours. This makes measles one of the most contagious diseases known to science—about 90% of people close to an infected individual will also become infected if they are not immune.

Symptoms of Measles
Early symptoms typically appear 7–14 days after exposure and may include high fever, cough, runny nose, and conjunctivitis (red, watery eyes). A few days later, a red, blotchy rash spreads from the head to the rest of the body. Koplik spots—tiny white lesions inside the mouth—are another early sign.

Why It Matters
Measles can lead to pneumonia, encephalitis (swelling of the brain), and death. One in five unvaccinated people in the U.S. who get measles will be hospitalized. Because of its ease of transmission, a single case can lead to large outbreaks in under-vaccinated communities.

If you suspect that you have measles isolate immediately and call your healthcare provider.

---

Sources:
Centers for Disease Control and Prevention. (2023). Measles (Rubeola). https://www.cdc.gov/measles/index.html
World Health Organization. (2022). Measles. https://www.who.int/news-room/fact-sheets/detail/measles