Even as campaigns to promote strong young women get national headlines, and toys designed to get girls interested in science and math receive popular acclaim, an alarming trend happens to many girls when they hit adolescence.

It’s a phenomenon called “losing their voice,” where even the most audacious girls are likely to become more cautious about speaking out and less likely to assert themselves.

Deborah Cihonski, a Chicago-based psychologist, said she was shocked at how much effort it took the girls in her study to decide when to speak up when they felt they had something important to say. They weighed everything from potential embarrassment to backlash before deciding to open their mouths. Often, they chose not to. What’s even more troubling is some of these young women continue to struggle with speaking up and asserting themselves later in life.

“Rather than speaking being their default, not speaking becomes the default and to speak up when it’s important is something that’s effortful for them,” Cihonski says.

Girls lose their voice for a variety of reasons–it’s mostly because of their self-esteem and is culture-based, says Martha Mendez-Baldwin, a psychologist who specializes in child and adolescent behavior, and an assistant professor of psychology at Manhattan College. Navigating the world between being children and women leave them unsure of how to act. When that uncertainty is met, combined with the pressure to fit in with peers and high expectations of parents, girls are often reluctant to assert themselves, she says.

In addition, girls receive tremendous pressure from society and media to adhere to a feminine role, says Linda Hoke-Sinex, a senior lecturer in the department of psychology and brain sciences at Indiana University in Bloomington, Indiana. The message is to be passive and nice–that it’s preferable to keep the peace than to speak up with an opinion that might be unpopular.

Girls receive tremendous pressure from society and media to adhere to a feminine role. The message is to be passive and nice.

Hoke-Sinex cites work by researchers Carol Gilligan and Lyn Mikel Brown who followed girls from roughly age 9 through age 16. At a certain point, the girls in the study stopped expressing their opinions, shutting down communication.