It’s often said that “no good deed goes unpunished”.

recent study asked participants to evaluate the performance of employees who offered to stay late to help a colleague prepare for an important meeting. When a man volunteered, he was rated 14% higher than a woman. If they both declined, the woman was rated 12% lower than the man. Saying ‘no’ meant the man was “busy”; the same response from the woman meant she was “selfish”.

Women had to give extra help just to get the same rating as a man.

This is the “office housework” that’s expected of women, whether she’s the receptionist who also bakes cupcakes for staff, or the manager who is expected to be the “office mommy”, placing her staff’s needs over her own. It’s no wonder that in an analysis of 183 different studies in 15 countries and multiple occupations, women were more likely to report feeling emotionally exhausted.

A few years’ ago, I came across a business memoir. In it, the writer, shared the best piece of business advice he ever got. He was told that, as a manager, people will come into his office and most of them will want to leave their problems with him. His job was to avoid taking ownership of others’ problems.

Office Mommies, (they can be men too), want to help and they may too readily acquire the responsibility for their colleagues’ tasks. I fell into this trap over-and-over in my own career and it easily—and unnecessarily— tripled my workload.

“Office housework” is a huge hidden drain on women’s productivity. As much as policies on child-care, maternity rights, access to higher education, and pay lift the glass ceiling, societal changes in expectations on women’s behavior are also necessary.

Much progress has already been made. For example, women’s enrolment in higher education is almost twice that of men, although their return-on-investment is typically lower than men’s. As a group, women are better qualified than men, yet earn three-quarters as much. Part of this may be attributed to different areas of specialization.

Women dominate education, social work and the humanities, whereas men choose higher-paying professions in computer science and engineering. Still, the traditional definition of gender behavior likely also plays a part. And, by the way, don’t you wonder that if men dominated social work it would pay a whole lot better?

You can’t consistently give your all at work as the “office mommy”. Those behaviors may be friendship builders but they’re not career boosters and, eventually, they’ll lead to burn-out. So, while we all want to be seen as “team players”, saying ‘no’ takes even more courage, and kindness—to ourselves.