The female contraceptive pill may affect how women perceive other women's attractiveness, a new study has suggested.

According to the women in the experiment, the higher the dose of oestrogen in the birth control they are using, the more likely they are to rank other women's appearance as very important to them, researchers found.

The study included 42 women using birth control pills containing both oestrogen and progesterone. Half of the women were taking ultra-low dose contraceptives and the other half were taking contraceptives with almost double the amount of oestrogen.

The women were then asked to rate pictures of both men and women and rated several attributes related to their appearance, such as their attractiveness and sex appeal, as well as other attributes including their perceived health and energy levels.

The results suggest that the way women rank other women's traits is likely related to the hormones in the contraceptives they are taking, particularly when viewed alongside results of previous similar studies, said researcher Valentina Piccoli of the University of Trieste, Italy.

"This mechanism may be a direct result of the hormones ingested via contraceptive pill use," or it could result from changes in the body's natural hormone levels that occur in women using the contraceptive, Piccoli told Live Science.

Previous research has shown a relationship between the levels of oestrogen in combined hormonal contraceptives and increased jealousy and so-called "mate-guarding behaviour," in which a person tries to ensure that his or her mate is not interested in pursuing other men or women.

The new findings show that oestrogen levels may be also be related to women paying more attention to potential female competitors, the researchers said.