Alba was born in Pomona, California. Her mother, Catherine, is of Danish, Irish, Scottish, Welsh, English, German and French Canadian ancestry and her father, Mark, is Mexican American, and is of Indigenous Mexican, Sephardic Jewish, Spanish and Mayan ancestry. She has a younger brother named Joshua. Alba's father was in the Air Force and his career caused them to live in many different places. They lived in Biloxi, Mississippi and Del Rio, Texas before returning to California at age 9. When she was young, Alba was ill many times. She had a collapsed lung twice, had pneumonia four or five times each year and had problems with her appendix and tonsils. She was in hospitals for much of her childhood. This meant Alba did not spend much time with other children. Alba has also said that she had obsessive-compulsive disorder when she was a child. The disorder affected her much less when her family moved to California. She graduated from high school when she was 16 years old. After high school, she went to the Atlantic Theater Company.