To answer this question you need look no further than the vignette entitled "Hairs," which comes towards the beginning of this excellent novella. This short fragment explores the way that hair is important as a symbol of difference, as, we are told, "Everybody in our family has different hair." Hair is important then in how it differentiates the members of Esperanza's family, but also it is incredibly important when she thinks of her mother's hair and the rich, sensuous images that come to her when they are close and she can smell the aroma of bread in her hair. Note what Esperanza says about her mother's hair:
But my mother's hair, my mother's hair, like little rosettes, like little candy circles all curly and pretty because she pinned it in pincurls all day, sweet to put your nose into when she is holding you, holding you and you feel safe, is the warm small of bread before you bake it, is the smell when she makes room for you on her side of the bed still warm with her skin, and you sleep near her, the rain outside falling and Papa snoring.
Thus we can see the importance of hair relates also to a feeling of intimacy, closeness and warmth that Esperanza experiences as a child, as she comes to associate the smell of her mother's hair with being close to her and being allowed in the same bed as a child. Hair, and the rich, evocative images it conjures up, are therefore very important as an image of closeness and family love and unity.