At one of my first jobs, I was blogging for an entertainment media company but was eager to take on extra script writing. Shortly after I was hired, another female writer came on board. My editors asked us who wanted to take on a new assignment, and I didn’t raise my hand. She landed the gig, and the next one too.

Now I realize why I held back—I was afraid our relationship would suffer. Anticipating a rift between us made me avoid competing with her altogether.

What I experienced is a real thing. Selin Kesebir, Ph.D., an assistant professor at London Business School, has studied how competition affects women’s relationships. Her team, along with researchers from the University College London School of Management, asked women and men to complete a simple typing task with same-gender and with opposite-­gender participants and rate how they felt afterward. The women going up against other women reported higher levels of negative emotions—like feeling nervous, insecure, or hesitant. Men competing with each other were more likely to report positive reactions; they felt energized and excited. And when the women went head-to-head with the guys? They didn’t feel as threatened as with their female peers, nor did they worry their relationships with the men would suffer. It was a girl-on-girl problem.

“When women had to compete with other women, they often felt like their relationship was negatively impacted,” says Kesebir. “Those feelings may lead women to avoid situations where they’d have to compete with female coworkers or to not compete as vigorously.” That means they may miss out on landing big career opportunities.

There are so many obstacles to the path of success; is it really possible that women are holding one another back? Yes, experts say, but the reasons run deeper than you may think. Take a look.

Girls aren’t exposed enough to healthy competition.

When girls play as kids, Kesebir says, “they try to make things equal, whereas boys try to decide who is better.” Boys’ activities are traditionally competitive, while girls’ focus on communal goals, like helping and supporting each other.

This made me think of when I was in sixth grade and I told a girl on my coed soccer team that I’d “kick her butt.” My coach told me to cut it out, and I asked why. “That’s how boys talk,” he said. Kesebir wasn’t surprised by my story. “The notion is,” she says, “that girls who try to compete tend to be disliked.”

The message to young women today is starting to change. Think of the Always #LikeAGirl campaign, which embraces feminine qualities as markers of strength, or the increased visibility of women in sports. “But generally,” says Kristen Liesch, Ph.D., a consultant on gender equality and diversity, “girls are still implicitly discouraged to behave in ways commensurate with competing, like leadership.”

Workplaces tend to be cutthroat rather than cooperative.

When Lauren, 37, started in marketing and communications in Los Angeles, she was assertive and ambitious, and viewed those qualities as strengths. She’d go after promotions and wouldn’t shy away from negotiating her pay. But a few months into the job, she saw the downside to a highly competitive workplace—her female boss seemed to be taking credit for the team’s work. And the other women were quick to go behind one another’s backs and throw another female colleague under the bus. So Lauren had to look out for herself. “It felt like only one of us could move up,” she says.