Despite decades of awareness, science is still inherently sexist. Women are vastly under-represented in professorships and in national academies worldwide. This is a familiar problem, but less highlighted is how the discrepancy plays out in the public arena of science — the media.

Male science pundits dominate television, radio and print — including the pages of opinion and comment in this journal. This imbalance cannot simply be explained by the shortage of female professors, as many male pundits are still at an early stage of their academic careers, when genders are better balanced. So what is behind this effective invisibility of women scientists in our media? And why does it matter?

Many people think that women themselves are to blame for the male-dominated media, in science and other subjects. Women, who often bear the brunt of domestic obligations, are said to have less time than men to participate in activities outside their work. And female colleagues tend to say that they do not feel eminent or qualified enough to comment. Perhaps this points to a question of confidence — one that does not seem to bother most men. Women may also be uncomfortable with the cut and thrust of conflict and debate. Indeed, at scientific seminars I have attended, most of the questions come from men, despite the audience usually containing an equal number of women. Voicing one's opinion in a public arena is a charged activity that seems to discourage many women, yet this is precisely the skill that a good pundit needs.

This still cannot explain the near-total absence of women pundits. Sexism must be responsible too. Having both the inclination and the time to do media work myself, I have certainly found myself dropped for programmes and replaced by less-qualified men. A prominent television producer once refused to put a colleague on screen because, he said, people wouldn't swallow science offered from "a young, blonde girl" like her. I have voiced opinions during panel discussions to little effect, then watched a man next to me say the same thing to widespread applause. In group discussions, I find that women are often talked over by men as if they weren't even in the room, whereas men are more likely to let other men finish their sentences. More insidiously, it is well documented that what passes for spirited assertion in men is interpreted, by both sexes, as unpleasant aggression in women. Given this bias, I understand why many women might prefer not to get involved.

Although these external factors and biases are out of our control, there are positive steps that women scientists can take to increase their visibility in the public arena. First and most importantly, women need to speak up. They could start in the relative safety of their own academic departments, preferably during their PhD studies. It is not easy — a famous female professor recently admitted to me that she still gets palpitations when asking questions at high-profile academic seminars — but nerves never killed anyone. Work through them, and you will gain respect as someone who has intelligent things to say and is not afraid to share them. Verbal sparring at seminars can also help your career because it builds confidence, develops an ability to communicate ideas and can even lead to collaborations. (And, palpitations aside, it gets easier with practise.) From speaking out at seminars, I found it natural to progress to media work, which, as well as being challenging and enjoyable, hones your powers of analysis and persuasion — skills that are useful for all scientists, regardless of sex.

Powers of analysis and persuasion are useful skills for all scientists, regardless of sex. ,

Second, keep in mind that, to the media and its audience, you don't have to be an eminent professor to have a valuable opinion — any PhD student or postdoc is miles ahead of the public in terms of scientific knowledge. Start a blog about your own research to refine your opinions and develop a style. As you gain more research experience, give your name and telephone number to your institution's press office, and don't shy away if asked. Similarly, don't be afraid to stray from your specialized niche of research expertise: if you are reasonably well read on a general topic, your opinion will still be useful. It is important to participate, because if we scientists aren't ready to step into the gap at short notice, the press may choose someone who isn't qualified at all — a real problem when the story is about homeopathy or other quackery.

Some might question if it matters whether we have more female science pundits, as long as the men are doing the job well. I think it does. A female messenger could attract a more diverse crowd, including other women. The point of punditry is often to persuade people that science is worthwhile and, more to the point, deserves funding. Also, pundits help to put forward scientific recommendations and counter misinformation. When it comes to controversial issues such as climate change, childhood vaccinations or genetically modified food, we need as many people as possible to hear and engage with our arguments. Women should stand shoulder to shoulder with their male colleagues to make this happen.