A study, published Monday in the Proceedings of the National Academy of Sciences journal, found women took sexy selfies in environments with greater economic inequality, rather than where they might be oppressed because of their gender.

The researchers analysed more than 68,000 sexualised self-portrait photographs, or "selfies," posted on social media platforms Instagram and Twitter across 113 countries.

They also looked at where in the world the most selfies were taken.

The researchers found the association between sexy-selfie prevalence and income inequality was directly related, with greater sexualisation in environments where incomes are unequal and people are preoccupied with relative social standing.

"We found no association with gender oppression," the study said.

"It's all about how women are competing and why they're competing," said the study's lead author, Khandis Blake from UNSW Science's School of Biological, Earth and Environmental Sciences.

She said women are "more likely to invest time and effort into posting sexy selfies online in places where economic inequality is rising, and not in places where men hold more societal power and gender inequality is rife".

Researchers in the past have found women take more selfies than men.

The PNAS researchers said income inequality increases competitiveness and status anxiety amongst people at all levels of the social hierarchy, making them sensitive to where they sit on the social ladder and wanting them to do better than others.

"Rightly or wrongly, in today's environment, looking sexy can generate large returns, economically, socially, and personally," Blake says.

"So, when a young woman adjusts her bikini provocatively with her phone at the ready, don't think of her as vacuous or as a victim.

"Think of her as a strategic player in a complex social and evolutionary game. She's out to maximise her lot in life, just like everyone."

Australian Associated Press