Measles has an incubation period of about 10 days (the delay between infection and the start of the illness).
At first the child develops a fever, runny nose, conjunctivitis and cough, and is generally unwell.
Two days after the start of the illness, Koplik spots appear. These are numerous small white spots on a granular red base inside the cheeks, opposite the back teeth.
After a further 2 days the typical pink or red blotchy maculopapular (both seen and felt) rash appears, starting on the face and neck and slowly spreading down to the hands and feet. The rash therefore appears 4 days after the child first becomes unwell.
The fever increases and the child becomes increasingly ill with the onset of the rash. Over a few days the rash fades, the temperature drops and the child feels better.
Skin pigmentation (brown) and peeling may follow the rash (post-measles staining).
The diagnosis is usually clinical but it can be confirmed by serum antibody tests.