The rubella virus is transmitted through respiratory droplets when an infected person coughs or sneezes. Transplacental transmission, especially in the first trimester of pregnancy, can cause serious birth defects. The disease is contagious from about 7 days before the rash appears until 5 to 7 days after it has subsided.

Complications seldom occur in children with rubella; when complications do arise, they commonly appear as hemorrhagic conditions such as thrombocytopenia. Many young women, however, experience transient joint pain or arthritis, usually just as the rash is fading. Fever may then occur, or recur. These complications usually subside spontaneously within 5 to 30 days. In very rare cases, otitis media and encephalitis may develop. When a pregnant woman contracts rubella, complications in the unborn child may be severe. (See Congenital rubella syndrome.)

In children, after an incubation period of 12 to 23 days, an exanthematous, maculopapular rash erupts abruptly. In adolescents and adults, prodromal signs and symptoms—headache, malaise, anorexia, low-grade fever, coryza, lymphadenopathy and, sometimes, conjunctivitis—are the first to appear. Suboccipital, postauricular, and postcervical lymph node enlargement is a hallmark of this disease and precedes the rash.

Typically, the rubella rash begins on the face and spreads rapidly, in many cases covering the trunk and extremities within hours. Small, red, petechial macules on the soft palate (Forchheimer sign) may precede or accompany the rash but aren’t diagnostic of rubella. By the end of the second day, the facial rash begins to fade, but the rash on the trunk may become confluent and be mistaken for scarlet fever. The rash continues to fade in the downward order, and generally disappears on the third day but may persist for 4 or 5 days—sometimes accompanied by mild coryza and conjunctivitis. In rare cases, rubella can occur without a rash. Low-grade fever may accompany the rash (99° to 101° F [37.2° to 38.3° C]), but it usually doesn’t persist after the first day of the rash; rarely, the body temperature may reach 104° F (40° C). A significant number of patients, 20% to 50%, are asymptomatic.