Álvarez's photography focused on documenting Mexico and its people during her lifetime, with a humanistic perspective. Her images document the industrialization of the country which occurred after the Mexican Revolution as well as the effects of 20th century technology. She did not like stylized studio shots, but wandered with her camera, searching for poignant moments and arresting compositions, which depicted the landscape, people and customs of Mexico. Typical are her photographs of indigenous women, like "Un descanso, llanto e indiferencia" (A Rest, Weeping and Indifference), from 1940, which portrays the exploitation and lonely suffering of its subject, or "El sueño de los pobres 2" (The Dream of the Poor, 2), in which a young boy lies sleeping amidst a collection of sandals. Álvarez noted that only the wealthy could dream of sweets, as young, poor Mexicans dreamed only of having shoes. Many of her works explore the intersections of light and shade, which she employed repeatedly as a metaphor in her works. In "Unos suben y otros bajan" (Some Go Up and Others Go Down), she used contrast to demonstrate mechanical patterns. In her 1950 work "En su propia cárcel" (In Her Own Prison), she used the cross-hatched shadows as an allegory for prison bars, trapping the young woman who leaned on a windowsill. In both "Tríptico del martirio" (Tryptych of Martyrdom, 1949), a series of photographs of prostitutes, and an untitled photograph of a masked gay rights activist (1982), Álvarez used the play of light and shadow to suggest erotic tension, as well as a social critique by obscuring the faces in darkness.