Mamá Ana
Mamá Ana is Rita's excitable, gregarious grandmother, with whom she spends the summer. Warm, short, and plump, with a passion for soap operas, Rita finds her attention suffocating. When Rita tries some deep breathing exercises, Mamá Ana interprets them as asthmatic wheezing and clucks over Rita's "condition" throughout the story. Initially Rita finds her grandmother smothering and invasive, but over time she comes to see her as having a way with people and "this talent for turning every day into a sort of party."

Maribel Hernández Jones
Maribel Hernández Jones is Angela's glamorous mother, a famous actress in toothpaste advertisements. She is wealthy from a previous marriage and lives in a pink house that Rita finds ridiculous, but she cares for her daughter enough to take her condition seriously. She calls in Papá Juan to cure Angela, and heeds his advice in cleansing her house of evil spirits and getting rid of her boyfriend.

Angela Hernandez
Angela is the anorexic girl whom Papá Juan is called to cure. She has stopped eating and communicating with her mother because of her mother's abusive boyfriend and his reported "bad influence." At Mamá's and Papá's prompting, the boyfriend is removed from the house, and as a result Angela's health improves. Because she has spent time in New York, Angela speaks English and shares with Rita a certain cross-cultural sophistication. She and Rita develop a friendship that helps make Rita feel connected on the island.

Meli
Meli is Rita's friend from home who gets sent to the convent for the summer. Rita and Meli got caught earlier trying to spend the night at Meli's boyfriend's house, which results in their grounding. Apparently she likes the retreat at the convent, because she plans to attend Catholic school in the fall.

Joey Molieri
Joey Molieri is Meli's boyfriend and Johnny's cohort in trying to seduce Rita and Meli. When Rita and Meli compare notes on the lines the boys used on them, they are identical.

Papá Juan
Papá Juan is Rita's eccentric, spiritualist grandfather. He is reportedly endowed with special gifts that give him insight into people's hearts. When Rita first arrives on the island she thinks her grandfather is senile because he comforts his emotional rooster and reports the contents of Rita's dreams. Although at first she satirizes Papá Juan's work by calling it Ghostbusting, she comes to recognize that he is an intuitive, perceptive man, and eventually even learns skills from him. His attempt to cure Angela and her mother of their "bad influence" sparks Rita's curiosity and draws her into life on the Island.

Rita
Rita is the sarcastic, fifteen-year-old narrator of "Bad Influence." When her story begins, she has been sent from her home in Paterson, New Jersey, to spend the summer with her grandparents in Puerto Rico. The visit is an alternative to a summer in a convent, and intended to keep her away from her boyfriend, Johnny Ruiz. Rita is furious as a result, and much of the story is her sarcastic, adolescent running commentary on her experience in Puerto Rico. Initially she makes every attempt to withdraw from her grandparents and life on the island, and describes their world through critical, and often hilarious, teenage eyes. Over the course of time, however, her interpretations soften as she makes a new friend and becomes engaged in the lives of her family and the ways of her homeland.

Rita's Mother
Rita's mother is responsible for sending her to the island for the summer and impeding her relationship with her boyfriend, so Rita resents her a good deal at the beginning of the story. When her mother joins her on the island later in the summer, she appears nervous, anticipating more of Rita's anger, but Rita has mellowed and they connect warmly.

Johnny Ruiz
Johnny Ruiz is Rita's boyfriend, and the cause for her summer's exile to the island. Rita says he can date any girl he likes, and he usually dates older girls and expects to have sex with them. Rita is caught trying to spend the night with Johnny, and after she is grounded he tells her that although he thinks her family is crazy, he will give her another chance in the fall. Rita's summer in Puerto Rico wears away some of Johnny's attractiveness, and by the end of the story she and Angela characterize him as a troubled young man.