There are plenty of reasons for people to get a bit grumpier as they age. Many of us gain more responsibilities to juggle as we get older. The resulting exhaustion wears on the nerves. Then there are all the usual petty indignities of age — the creaky knees, sore backs, bottles of hair dye. Those cheer no one up either.

But perhaps the most annoying aspect of growing older for women is the biases and stereotypes you’re confronted with. Sure, people may underestimate or inappropriately sexualize younger women (and that’s no picnic). But cross the boundary of 40 and suddenly you have another problem: when people look at you, they automatically think of their nagging mom, kooky aunt, or cranky battle ax of a boss.

Don’t believe me? Then I have a wildly annoying new study out of UC Berkeley to show you.

Middle-aged women versus outdated stereotypes

As Berkely Haas News reports, the study was inspired by the personal experiences of Jennifer Chatman, a tenured professor at the university’s Haas School of Business who has won many teaching awards, and received glowing student feedback earlier in her career. But when she hit 40, something weird happened.

While Chatman felt objectively better at her job — she had more experience and knowledge under her belt, after all — her student evaluations began to decline. Why might that be, she wondered?

To investigate, she rounded up a group of colleagues and conducted a series of experiments, the results of which were recently published in the journal Organizational Behaviour and Human Decision Processes. Warning: if you are a middle-aged woman, they may make your head explode from sheer rage.

Whether the research team asked volunteers to rate fictional supervisors or dug into mountains of data on student evaluations throughout professors’ careers, the conclusion was the same. As women enter middle age, others tend to automatically see them as less warm and therefore less likable. And that’s true even if literally nothing changes about them except for the number of candles on the birthday cake.

In one study, the researchers gave volunteers short profiles of a fictional boss. All the details of these profiles were the same except from the name. Sometimes the boss was named “Sue,” other times “Steve.” Despite the profiles containing identical information, participants rated middle-aged “Sue” as significantly less warm and friendly.

“It’s just stunning,” Chatman says. “These stereotypes are so hardwired and deeply entrenched that they come out even when absolutely identical information is provided about a man and a woman.”

Yet another hurdle for ambitious women

It is of course infuriating that people are primed to see women of a certain age as, in the vernacular, bitches. Chatman points out it is also a big block to their career advancement.

“Middle age is a make-or-break time, when people are being groomed and considered for the top jobs,” she commented. “We have to look beyond the pipeline to see what’s actually happening in terms of the experiences women are having throughout their careers.”

Tired stereotypes of middle-aged women as naggy, frumpy, and grumpy create an additional barrier to female advancement. At just the age that many professional women have accumulated the skills and contacts they need to soar in their careers, they are saddled with outmoded expectations that can prevent them from reaching their full potential.

You’re plenty nice, it’s the world that has to change

What’s the takeaway here? If your first impulse is to counsel middle-aged women to act nicer at work, maybe take a pause. (And not just because our cheeks are already aching from all the fake smiling we do.) The problem here isn’t that middle-aged women are actually grumpy, rude, or sour-faced. The problem is bias in society. That’s what needs to change, according to the researchers.

“I would hate for the message to be that women need to be more careful about how they present themselves,” says Chatman, “because these findings already point to the fact that women have a narrower band of acceptable behavior.”

Instead, the researchers hope their work will nudge bosses to be more thoughtful when judging employees. If you know that nearly all of us have been exposed to these stereotypes, you’ll be better placed to make sure they don’t creep in when you’re evaluating employees.