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

Measles is caused by a virus that travels through respiratory droplets—the tiny particles released when an infected person coughs or sneezes. Once someone breathes in the virus, it infects the lungs and spreads through the bloodstream. The infection triggers a characteristic sequence: fever and cold-like symptoms first, followed days later by a distinctive rash that starts on the face and spreads downward across the body.

The disease is highly contagious. If one person with measles is in a room, about 9 out of 10 unvaccinated people who share that space will catch it. The virus can linger in the air or on surfaces for up to two hours after an infected person leaves. Most people who get measles recover within one to two weeks, but the infection can cause serious complications, particularly in young children, pregnant women, and people with weakened immune systems.

Key Takeaways

  • Measles starts with fever, cough, and runny nose, then progresses to a rash that appears first on the face and spreads downward.
  • The virus spreads through the air when infected people cough or sneeze, making it one of the most contagious respiratory infections.
  • Doctors identify measles by recognizing the pattern of symptoms and the appearance of the rash, sometimes confirmed with a blood test.
  • Complications can include pneumonia, brain inflammation, and ear infections, which is why early recognition matters.
  • The MMR vaccine prevents measles in most vaccinated people and is given as two doses starting at age 12 months.

The three stages of measles infection

Measles unfolds in a predictable pattern. The first stage, called the prodromal phase, lasts about three to four days. During this time, an infected person develops a high fever (often above 103°F), a dry cough, a runny nose, and sometimes red, watery eyes. These symptoms look like a common cold or flu, which is why measles can be missed early on.

The second stage is when the rash appears. Before the rash shows up, small white spots with red halos (called Koplik spots) appear inside the mouth on the cheeks opposite the molars. These spots are a reliable sign of measles and typically fade as the rash develops on the skin. The skin rash starts as small red bumps on the hairline and forehead, then spreads down the face, neck, trunk, and finally the arms and legs over the course of three to four days.

The third stage is recovery. The fever usually peaks when the rash is most widespread, then gradually falls over three to four days. The rash fades in the same order it appeared—face first, then downward—and may leave behind a slight brownish discoloration or flaking skin. Most people feel significantly better once the fever breaks, though cough and fatigue can linger for weeks.

How doctors recognize measles

A doctor typically diagnoses measles by recognizing the pattern of symptoms and the appearance of the rash. The combination of high fever, the three-day cough-runny nose-eye redness pattern, followed by the characteristic rash spreading from face downward, is distinctive enough that a doctor may diagnose measles based on clinical observation alone.

If confirmation is needed—particularly early in the illness or when symptoms are unclear—doctors order a blood test. The test looks for antibodies the immune system produces in response to the measles virus, or it detects the virus itself using a method called RT-PCR. A throat or nasal swab can also be tested. Results typically come back within one to two days.

Timing matters for testing. The blood test is most reliable after the rash appears. If a doctor suspects measles before the rash develops, a throat or nasal swab is more likely to detect the virus. Once someone has had measles, they develop lifelong immunity—they cannot catch it again.

Complications that can develop during measles

Most children recover from measles without lasting problems, but complications occur in about one out of every four to five cases. Pneumonia is the most common serious complication, particularly in children under five. It develops when the measles virus or a secondary bacterial infection affects the lungs, causing difficulty breathing and persistent cough.

Encephalitis—inflammation of the brain—is rare but serious. It can develop during the acute illness or weeks later. Signs include high fever, severe headache, stiff neck, confusion, or seizures. Subacute sclerosing panencephalitis (SSPE) is an extremely rare but fatal condition that can develop years after measles infection in people who were infected as infants or young children.

Other complications include ear infections, which can cause hearing loss; diarrhea and vomiting; and secondary infections from bacteria. Pregnant women who catch measles face increased risk of miscarriage or premature delivery. People with weakened immune systems—from HIV, cancer treatment, or immunosuppressive medications—can develop severe, prolonged measles that may be life-threatening.

Why measles spreads so easily

Measles is one of the most contagious human diseases. A person with measles is contagious from about four days before the rash appears until four days after it appears. During this window, they shed virus particles in respiratory droplets every time they cough, sneeze, talk, or breathe. These droplets can travel across a room and infect anyone who inhales them.

The virus can also survive on surfaces. If someone touches a contaminated surface and then touches their face, they can become infected. In an enclosed space with poor ventilation—like a classroom, waiting room, or airplane—the virus spreads rapidly. This is why measles outbreaks in communities with low vaccination rates can grow quickly and affect dozens or hundreds of people within weeks.

When to contact a doctor about possible measles

Contact a doctor if you or a family member develops a high fever followed by a cough, runny nose, and red eyes—especially if a rash then appears. Do not wait to see if symptoms improve on their own. Early recognition allows a doctor to confirm the diagnosis, monitor for complications, and advise on isolation to prevent spread to others.

Seek immediate medical attention if measles is accompanied by difficulty breathing, severe headache, stiff neck, confusion, or seizures. These signs suggest a serious complication like pneumonia or encephalitis. When you call a doctor's office or clinic, mention that you suspect measles before arriving, so staff can take precautions to prevent spread to other patients and staff.

If you are unsure whether you or a family member has had measles or been vaccinated, a doctor can review your medical records or order a blood test to check for immunity. Knowing your measles status matters, especially if you plan to travel internationally or work in healthcare.

Frequently Asked Questions

Can someone get measles twice?

No. Once you recover from measles, your immune system produces antibodies that protect you for life. You cannot catch measles a second time. However, immunity from vaccination can wane slightly over decades, which is why the MMR vaccine is given as two doses—the second dose boosts protection to near 100 percent.

Is measles the same as German measles?

No. Measles and German measles (rubella) are caused by different viruses and produce different rashes. Measles rash is red and bumpy and spreads from face downward. Rubella rash is finer and lighter and often starts on the face but spreads more evenly. Both are prevented by the MMR vaccine, but they are distinct infections.

What should someone do if they think they have measles?

Call a doctor before visiting in person so the office can prepare and prevent spread to others. Stay home and avoid contact with unvaccinated people, pregnant women, and people with weakened immune systems. Rest, drink fluids, and take over-the-counter fever reducers as directed. A doctor will advise on isolation duration and watch for complications.

Can measles be treated with antibiotics?

No. Antibiotics kill bacteria, not viruses. Measles is viral, so antibiotics do not treat the infection itself. Treatment focuses on managing symptoms—fever, cough, and discomfort—while the immune system fights the virus. Antibiotics may be used only if a bacterial infection develops as a complication, such as a secondary ear or lung infection.

Who should not receive the MMR vaccine?

Infants under 12 months, people with severe allergies to vaccine ingredients, and people with certain immune system disorders should not receive MMR. Pregnant women should not be vaccinated, though they can be vaccinated after delivery. People taking certain medications that suppress the immune system should discuss timing with their doctor before vaccination.