Rubella is an infection caused by a virus. It is usually mild with fever and a rash. About half of the people who get rubella do not have symptoms. If you do get them, symptoms may include
A rash that starts on the face and spreads to the body
Mild fever
Aching joints, especially in young women
Swollen glands
Rubella is most dangerous for a pregnant woman's baby. It can cause miscarriage or birth defects.
Rubella spreads when an infected person coughs or sneezes. People without symptoms can still spread it. There is no treatment, but the measles-mumps-rubella (MMR) vaccine can prevent it.
Centers for Disease Control and Prevention