Alba was born in Pomona, California to Catherine (née Jensen) and Mark Alba. Her mother is of Danish and French Canadian descent and her father is Mexican American. She has a younger brother, Joshua. Her father's Air Force career took the family to Biloxi, Mississippi and Del Rio,
Texas, before settling back in California when she was nine years old. Alba described her family as being a "very conservative family – a traditional, Catholic, Latin American family" and herself as very liberal; she says she had identified herself as a "feminist" as early as age five. Alba's early life was marked by a multitude of physical maladies. During childhood, she suffered from partially collapsed lungs twice, had pneumonia four to five times a year, as well as a ruptured appendix and a tonsillar cyst. Alba became isolated from other children at school,
because she was in the hospital so often due to her illnesses that no one knew her well enough to befriend her. Alba has also had asthma since she was a child. Alba has said that her family's frequent moving also contributed to her isolation from her peers. She has acknowledged that she has suffered from obsessive–compulsive disorder during her childhood. Alba graduated from high school at age 16, and she subsequently attended the Atlantic Theater Company
