What Measles Does to the Body
Measles has surged across the United States in recent years, with a national case count for 2026 that dwarfs the 2025 tally. Alarmingly, that count includes a growing number of measles-related deaths—making vaccination an increasingly crucial tool for preventing the disease.
"Measles is one of the most infectious diseases we have," says Columbia pediatrician Irene Frantzis, MD. "And once you get measles there's no medication to treat the infection, making it hard to prevent complications."
Dr. Frantzis, an infectious disease specialist, explains how measles affects the body, causing serious, sometimes fatal, complications.
How does measles infection begin?
Measles infection usually starts in the respiratory tract after exposure to the virus through particles and droplets suspended in the air. From there, the virus enters the bloodstream and circulates to the lymph nodes, where it can stay for up to three weeks without causing symptoms. After this incubation period, the virus leaves the lymph nodes and moves to different parts of the body, where it starts to cause symptoms.
Because the virus enters through the respiratory tract, the first symptoms typically resemble a head cold with runny nose, conjunctivitis (red eyes), sore throat, ear pain, and cough. In younger children, measles can cause croup, a severe cough resulting from swelling in the larynx and airway. A high fever often occurs in the beginning stage of infection. People with measles usually feel very unwell.
Why does measles cause a rash, and how is it different from other rashes?
The virus travels to the skin and infects cells on the surface (epithelial cells), triggering an inflammatory response that causes red spots. This rash appears about four days after initial fever and cold symptoms and usually lasts about a week. Although it can look like rashes caused by other viruses, a measles rash starts on the head behind the ears or around the hairline then moves down to the rest of the body.
What are some common complications of measles?
As it travels through the body, measles virus can damage the layer of tissue that lines our organs. In the lungs, the virus can trigger an influx of white blood cells, causing pneumonia.
The damage done by the virus also allows bacteria to cause new infections, including ear infections and bacterial pneumonia, even after you've recovered from the virus.
Measles can disturb the gastrointestinal tract, causing diarrhea and vomiting that can lead to dehydration. Enlarged lymph nodes in the GI tract can cause abdominal pain.
Are more serious complications possible?
Yes. About 1 in 1,000 people with measles will develop encephalitis (brain inflammation) during the acute stage of infection, which often results in permanent brain damage. Some people develop encephalitis even after they have cleared the virus. Encephalitis can cause additional complications, such as seizures, coma, cognitive impairment, deafness, or motor disabilities, and can sometimes be fatal.
Children who get the measles before the age of one are at higher risk for subacute sclerosing panencephalitis (SSPE), a rare but usually fatal condition that affects the central nervous system about 7 to 13 years after initial infection. The condition affects different parts of the brain, causing motor problems and sensory loss. Within two to three years, people with SSPE are no longer able to regulate their breathing, heart rate, and blood pressure.
Measles can also cause immune amnesia, in which your immune system 'forgets' how to respond to other diseases you have encountered previously or been vaccinated against.
The risk of serious complications is higher in babies and young children, young adults, pregnant women, and people with weakened immune systems.
What makes the measles virus so contagious?
Before the rash appears, people with measles may think they have a common cold, so they may not isolate themselves. But someone infected with measles can shed the virus as early as four days before the rash appears (when they are coughing and experiencing other respiratory symptoms) to as late as four days after the rash resolves.
What's more, the virus can stay in the air for about two hours, even after the infected person has left the room.
In fact, measles is so contagious that if an infected person steps into a room with 10 unprotected people, 9 of those people will become infected.
How can people protect themselves from measles?
The best way we know to prevent measles infection is to get vaccinated. One dose of the MMR vaccine provides about 93% protection, and two doses brings that up to 97%. For children who are not able to receive the vaccine due to medical reasons, it's important that they are surrounded by people who are vaccinated to reduce their risk.