A "comprehensive survey" by Sydney recruitment firm Salt and Shein, found that these areas have become practically male-free zones.
"I don't believe gender imbalance is good for any profession," news.com.au quoted an anonymous senior female executive as saying.
"I really worry that it makes us appear to be a bit of a 'pink ghetto', so that we're perhaps taken less seriously by management," she said.
Salt and Shein director Peter Salt said the survey asked top-level managers what kept them up at night and the consensus was that gender imbalance was a big issue.
"There is this topic of pink ghettos.
"What they're talking about is gender diversity. There has long been a debate about board representation... this is the same but in reverse," he said.
Senior executives surveyed said having too many women meant they were "pigeonholed" in certain roles, that there was a "logistical nightmare" managing maternity leave and flexible working arrangements for mothers, and ultimately a lack of diverse views.
Salt's partner Josh Shein told advertising website AdNews that "girls and gay blokes gravitate to PR" because it's "softer" and more creative.
"Women often need to take maternity leave and that damages their credibility of being an executive. It's seen as putting their careers as second," he added.
Equal Opportunity for Women in the Workplace Agency director Helen Conway said companies that didn't practise good "talent management" ended up with pools of women stagnating in support roles, and that ultimately the company itself would be worse off.
"Our view is that an all-female environment is bad, and an all-male environment is bad.
"You need balance. You need diversity to optimise performance," she said.
Salt said the increasing proportion of women in PR and corporate affairs had been happening for at least a decade, and it was not clear what was keeping men out.
"This is the challenging bit we're trying to get to the bottom of.
"There seems to be more male representatives at the very very top and greater representations of females on the way through," he said.