Lead author Sarah Killoren, an assistant professor of human development and family studies at the University of Missouri, said sisters most frequently played the role of confidant, giving information about themselves and asking for more information about their sisters' lives.
Disclosures made during their conversations revealed levels of intimacy between sisters, Killoren said.
"Our findings indicate that sisters play important roles as adolescent girls form ideas about romantic relationships and sexuality," Killoren said in a statement. "Sisters are important communication partners when it comes to these sensitive topics."
The second role, as source of support, was displayed when sisters encouraged siblings' ideas about dating and sexuality.
The mentor role was displayed when sisters served as role models for one another, most frequently by giving advice.
"Given their age, older sisters were more likely to have advice to share and have romantic relationships and sexual experiences from which their younger sisters can learn," Killoren said.
Younger sisters commonly reported learning from older sisters' experiences, especially their older sisters' negative dating and sexual experiences, Killoren said.
"Younger sisters frequently commented on their older sisters' negative experiences, such as teen pregnancy and abusive relationships, and made decisions to be different," Killoren said. "Learning only from negative experiences could occur because younger sisters only consciously identify the experiences of their sisters that they do not want to repeat."
The findings were published in the journal Family Relations.