Measles is a viral infection that spreads through the air and causes fever, rash, and cough

Measles is caused by a virus that travels in droplets when an infected person coughs or sneezes. You catch it by breathing in those droplets or by touching a surface they landed on, then touching your face. The infection starts in your lungs and spreads through your body, triggering fever, a distinctive rash, and respiratory symptoms. Most people recover on their own, but measles can cause serious complications, especially in young children, pregnant people, and adults with weakened immune systems.

The virus is highly contagious — if one person has measles and is not immune, about 9 out of 10 people around them will catch it. This is why measles spreads quickly in communities where vaccination rates are low. Once you have had measles or been vaccinated against it, you are protected for life.

Key Takeaways

  • Measles spreads through the air when an infected person coughs or sneezes, making it one of the most contagious viruses.
  • Symptoms appear 10 to 14 days after exposure and include high fever, cough, runny nose, and a rash that spreads from the face downward.
  • Serious complications include pneumonia, encephalitis (brain inflammation), and ear infections, which occur more often in children under 5 and adults over 20.
  • The MMR vaccine prevents measles and is given in two doses starting at age 12 months, with protection lasting your entire life.
  • There is no specific treatment for measles itself — care focuses on managing fever and symptoms while your immune system clears the virus.

How measles symptoms develop and what to expect

Measles has two stages. The first stage lasts 3 to 7 days and feels like a cold or flu: high fever (often above 103°F), cough, runny nose, and sore throat. You may also notice small white spots with red halos inside your mouth — these are called Koplik spots and appear 2 to 3 days before the rash.

The second stage is the rash. It starts on your face and hairline, then spreads down your neck, trunk, and limbs over the next few days. The rash is red and bumpy, and it itches. As the rash spreads, your fever may spike even higher. The rash fades in the same order it appeared — face first, then body — and usually clears within a week.

During this entire illness, you are contagious from 4 days before the rash appears until 4 days after it appears. This means you can spread measles to others before you even know you have it.

Who is at highest risk for serious measles complications

Most healthy adults and older children recover from measles without lasting problems. But certain groups face much higher risk of complications. Children under 5 are most vulnerable — they are more likely to develop pneumonia, ear infections, and encephalitis. Adults over 20 also have higher complication rates than teenagers and young adults.

Pregnant people who catch measles can have miscarriage or deliver early. Babies born to mothers who had measles during pregnancy may have birth defects. People with weakened immune systems — from HIV, cancer treatment, or immunosuppressive medications — can develop severe pneumonia and other life-threatening infections.

Even people who recover can face delayed complications. Subacute sclerosing panencephalitis (SSPE) is a rare brain disease that can develop years after measles infection, usually in people who were infected before age 2. It is fatal and has no cure.

Common complications that can follow measles

Pneumonia is the most common serious complication, occurring in about 1 out of 20 infected children. It can develop during the measles illness or after the rash fades. Encephalitis (inflammation of the brain) happens in about 1 out of 1,000 cases and can cause seizures, confusion, and permanent brain damage.

Ear infections occur in about 1 out of 10 infected children and can lead to hearing loss. Diarrhea and other digestive problems are common, especially in young children, and can lead to dehydration. Some people develop thrombocytopenia (low platelet count), which causes unusual bleeding or bruising.

Secondary bacterial infections can occur when measles damages the lining of your respiratory tract, making it easier for bacteria to invade. These infections may require antibiotics. Most complications appear while you still have the rash or shortly after it fades.

Why the MMR vaccine prevents measles

The MMR vaccine contains weakened or inactivated forms of three viruses: measles, mumps, and rubella. When you receive the vaccine, your immune system recognizes these harmless versions and builds antibodies against them. If you are later exposed to the real measles virus, your immune system recognizes it immediately and stops the infection before it takes hold.

The vaccine is given in two doses. The first dose is typically given at 12 to 15 months of age, and the second at 4 to 6 years old. Two doses provide lifelong protection — studies show immunity lasts at least 50 years and likely for life. If you were vaccinated only once or are unsure of your vaccination history, a second dose can be given at any age.

A small number of people do not develop immunity after vaccination, usually because their immune system was not ready to respond at the time of vaccination or because of an underlying immune condition. This is why high vaccination rates in the community matter — they protect people who cannot be vaccinated and those whose vaccines did not work.

What happens if you think you have measles

If you develop fever, cough, and rash, contact your doctor or urgent care clinic by phone before you go in. Tell them you think you might have measles so they can prepare and prevent spread to other patients. Do not show up without calling first. Your doctor can examine you and may order a blood test or throat swab to confirm measles.

While you are sick, stay home and away from other people, especially infants, pregnant people, and anyone with a weakened immune system. Wash your hands frequently, cover your cough, and disinfect surfaces you touch. There is no specific antiviral treatment for measles — your doctor will focus on managing your fever with over-the-counter pain relievers and keeping you hydrated.

If you develop difficulty breathing, severe headache, confusion, or chest pain, seek emergency care. These can signal pneumonia or encephalitis. If you are pregnant, have a weakened immune system, or are caring for a young child with measles, talk to your doctor about whether you need closer monitoring or additional support.

Measles outbreaks and why they happen

Measles outbreaks occur when vaccination rates in a community drop below a certain threshold. Because measles is so contagious, communities need about 95% of people to be vaccinated to prevent the virus from spreading. When vaccination rates fall below this level, the virus can spread rapidly through unvaccinated people.

Outbreaks often start when an unvaccinated person travels to a country where measles is still circulating, catches it, and brings it home. In communities with low vaccination rates, the virus then spreads from person to person. Schools, childcare centers, and healthcare settings are common places where measles spreads quickly because people are in close contact.

During an outbreak, unvaccinated people and those who cannot be vaccinated face the highest risk. Public health agencies track cases, notify people who may have been exposed, and work to increase vaccination rates to stop the spread.

Frequently Asked Questions

Can you get measles twice?

No. Once you have had measles or been vaccinated against it, you have lifelong immunity. Your body remembers how to fight the virus and will stop it if you are exposed again. This is why measles vaccination is so effective — one or two doses protect you for your entire life.

Is the MMR vaccine safe?

Yes. The MMR vaccine has been used for over 50 years and has been given to hundreds of millions of people worldwide. Serious side effects are extremely rare. Common mild side effects include soreness at the injection site, low fever, or rash a week or two after vaccination. These are signs your immune system is responding and are not dangerous.

What should I do if I was exposed to measles but am not vaccinated?

Contact your doctor or health department right away. If you are not immune and were exposed, you may be able to receive the MMR vaccine or an injection of antibodies (immunoglobulin) within a few days to prevent infection or reduce severity. Time matters — the sooner you act, the better the protection.

Can adults who were vaccinated as children still catch measles?

Very rarely. Two doses of MMR vaccine provide protection in about 97% of people. The small percentage who do not develop immunity usually have an underlying immune condition. If you are unsure whether you were vaccinated or received only one dose, a second dose can be given safely at any age.

Why do some people still get measles even though they were vaccinated?

Vaccine failure is rare but possible. Some people's immune systems do not respond well to the vaccine, especially if they were vaccinated very young, had an underlying immune condition, or received the vaccine while their immune system was fighting another infection. This is why vaccination rates matter — high community immunity protects the small number of people whose vaccines did not work.