About Rubella. Rubella — commonly known as German measles or 3-day measles — is an infection that mostly affects the skin and lymph nodes. It is caused by the rubella virus (not the same virus that causes measles). Rubella spreads when people breathe in virus-infected fluid, such as the droplets sprayed into the air when a person with rubella sneezes or coughs, or share food or drink with someone who's infected.