Measles is a highly contagious viral disease most recognizable for causing fever and rash. It usually affects children and can be fatal when it finally affects the respiratory system, most commonly leading to pneumonia. Other serious complications include diarrhea, ear infection, and encephalitis or swelling of the brain. However, infection or complete vaccination can both confer lifelong immunity.

The measles virus is very easily spread via infected airborne particles produced by coughing, sneezing, or even just talking. These particles can then be inhaled by another person, thus causing infection. The virus can also be spread through direct contact with infectious droplets, as when a person touches a surface containing such droplets and subsequently touches his eyes, nose, or mouth.

The symptoms of measles usually appear 10-12 days after infection, and last for 7-10 days. A person with measles is considered contagious as early as 4 days before symptoms appear, and up to 4 days after the characteristic rash has appeared. Measles typically begin with a high fever, cough, runny nose, and red, watery eyes (conjunctivitis). As such, the start of a measles infection can be easily confused with any other upper respiratory tract infection (cough and colds). 2-3 days after the start of symptoms, distinct white spots called Koplik spots can appear inside the mouth. These spots do not always appear, but when they do, one can be sure that the individual has a measles infection. 3-5 days after the start of symptoms, the distinctive rash–flat red spots with small red bumps–appears. The rash usually starts behind the ears and the hairline, and gradually spreads downwards, from the face to the neck, trunk, legs, and feet to cover most of the body. The rash may be itchy and can coincide with a high fever. After that, the symptoms will start to resolve.

In most cases, measles resolves on its own, as the body gradually builds immunity against it. There is no specific treatment against the virus. Thus, treatment is usually just supportive care, which includes having a nutritious diet, adequate fluid intake or rehydration (especially if the patient develops diarrhea) and enough rest. It is important for patients with measles to be assessed by a physician, who may also give other medications to address the complications (e.g. antibiotics for complicated infections like pneumonia and ear infections, rehydration for diarrhea). Vitamin A supplementation may also be recommended, since Vitamin A deficiency is a known risk factor for developing more severe measles.

Vaccination against measles confers lifelong immunity. As much as possible, the vaccine should be administered during the routine, doctor-recommended schedule during infancy and childhood (beginning as early as 9 months) to provide protection as early as possible. It is usually given as a combination that also protects against rubella and mumps.