A leading scientist at international athletics’ governing body has said he is in favour of a third category for intersex athletes and that it could happen within five years – although he admitted public opinion will have to shift first.

Dr Stéphane Bermon, who heads the IAAF’s health and science department, told the Guardian that while he was speaking in a personal capacity he had the “feeling some day it will happen, and probably in five or 10 years”.

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However, Bermon said: “My feeling is also the public is not ready for this. We don’t want to stigmatise athletes. We also have to take into account religious and cultural sensitivities. So basically I am in favour but there needs [to be] some changes in public opinion.”

Bermon’s comments came on the day the IAAF published new rules that will require women with high testosterone levels to take a pill to lower it below five nanomoles per litre if they want to compete internationally at distances ranging from 400m to a mile.

Females who do not abide by the rules, which come into force on 1 November, will still be eligible to compete in non-international competitions or in the male classification.

The policy has already proved controversial, with some feeling it unfairly targets Caster Semenya, the two-time 800m Olympic champion who underwent gender testing in 2009. The South African appeared to express her displeasure by tweeting: “I am 97% sure you don’t like me but I’m 100% sure I don’t care.”

However Bermon insists the issue was more prevalent than is realised. “We have a lot of athletes with this kind of condition. It is not just the one or two people you hear about in the media. In elite female athletics the number of intersex athletes is 140 times more than what you might find in the normal female population.”

Nevertheless it remains a difficult and sensitive issue, and Semenya has born the brunt of it since she burst on to the world stage as a shy 18-year-old by winning the 800m at the 2009 world championships. That led to gender tests that were never made public but were alleged, according to Australia’s Daily Telegraph, to show she had no womb or ovaries but had internal testes.

In 2011 the IAAF introduced a testosterone limit and Semenya was not quite the same athlete. She was beaten by Mariya Savinova at that year’s world championships and at London 2012, although she was later upgraded to gold medals after the Russian was convicted of doping. The IAAF was accused of violating Semenya’s human rights, gross insensitivity and even racism. It insisted it was merely trying to ensure women with higher testosterone do not have an unfair advantage. Arguments flared, subsided and flared again; Semenya mostly suffered in silence.

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However in 2015 the court of arbitration for sport suspended the IAAF’s rules on hyperandrogenism following a legal challenge by the Indian sprinter Dutee Chand, which meant Semenya was free to race without medication. She has been unstoppable ever since.

Yet her situation appears likely to change again. When Cas suspended the hyperandrogenism rules it asked the IAAF to come up with evidence to show that high testosterone does make a significant difference to performance.

The IAAF believes it has done that following research from Bermon, who analysed blood samples from male and female athletes at the 2011 and 2013 world championships. When he examined women with very high testosterone in 2011, who subsequently took hormone-suppressing treatment, he found their performance decreased by 5.7% on average in 2013.

Sebastian Coe, the president of the IAAF, said the new rules are solely about ensuring equal conditions for all athletes.

“Like many other sports, we choose to have two classifications – men’s events and women’s events. We need to be clear about the competition criteria for these categories. Our evidence and data show that testosterone, either naturally produced or artificially inserted into the body, provides significant performance advantages in female athletes.”

Bermon rejected the suggestion the policy is unfair because it targets women born with natural advantages – not unlike those enjoyed by Usain Bolt by being tall and having fast-twitch muscle fibres.

“Historically the reason why we have separate male and female categories is that otherwise females would never win any medals,” Bermon added. “Testosterone is the most important factor in explaining the difference. We are talking about females competing with levels similar to males. Very often it is more than 20 or 25nmol/L. So it is very high.”

This, however, is unlikely to be the end of the matter. The IAAF is already bracing itself for another challenge at Cas, although it believes it has a robust case.

Semenya, meanwhile, knows her world could be slowing down again. The sports scientist Ross Tucker predicts she could run the 800m between five and seven seconds slower next year if she takes testosterone-suppressing medication. Whether that is right and proper will be fiercely debated in the months ahead.