The pants arrived today. They’re bright pink with the word HOTTER emblazoned on them in red letters. “We’ve always had cheap pants that were drawn on,” says Ell Potter, stretching the elastic. She drops them on the table and grins at Mary Higgins. After two years, the pair’s debut Edinburgh fringe show has made it to one of London’s coolest theatres. Hence the underwear upgrade.

Hotter is their sweaty interrogation of the female body, its fluids, desires and changes. The duo, both 23, are more used to conducting interviews than giving them. For the show, they quizzed women and non-binary people between the ages of 11 and 97. Questions ranged from a simple choice – hot or cold? – to deeper queries about the strengths, uses and failings of their bodies.

On stage, Higgins and Potter lip sync to these voices, adopting their interviewees’ postures and pouts as they analyse their anatomies. Their own stories are peppered throughout. “We wanted to have the same experience,” says Higgins. “That release of talking openly.” Indeed, part of the show’s attraction is its brutally honest comedy, both from the performers and their interviewees. It’s feel-good, but there’s no pretence of perfection. “Lots of people said they’d never said these things out loud before,” remembers Potter.

The two speak breathlessly, each catching the other’s train of thought and taking over. Until now, it’s always been just the two of them in a rehearsal room, but for the Soho show they’ve brought Jessica Edwards on board as director. “She lets us take risks,” Potter says. Higgins nods: “She doesn’t have a student brain like we do.”

The two barely knew each other at Oxford University, until Higgins asked Potter to make a show with her and they started dating. They came up with Hotter, merging their surnames to to form the show’s title, they booked their Edinburgh venue, then they broke up.

They pushed through the first run, receiving favourable reviews but feeling dishonest in their refusal to talk about what they had been through together. “The whole show was about bodies,” says Potter, “and most of what I’d learned about mine was through Mary.” In the updated versions, they have held nothing back. “It’s far more explicit,” says Potter. “We’re trying to push it more, be braver.” Higgins smiles. “We’ve grown up with it.”

As young queer women who have both struggled with their weight, they are aware of the silence and awkwardness that can surround women’s bodies. From their interviewees, they’ve learned this only grows with age. “If the menopause happened to men,” sighs Higgins, “oh my God, we’d know so much more about it.”

When Higgins interviewed her mum, she realised she was “just weathering this storm in silence. She had a hot flush at work recently for about 20 minutes, bright red. You should be able to say, ‘Sorry, I’m a tomato!’” Her arms are everywhere as she relays this story – a mixture of laughter and dismay. “It’s the silence that just kills me. Silence leaves so much room for embarrassment.”

The pair have just secured arts council funding for their next show, Fitter. They pitch it as “Hotter’s greasy younger brother” and for it they’re interviewing male, trans-male and masculine-presenting people about ideas of fitness and what it means to fit in. Hotter’s popularity has made it easier to find a wide range of interviewees, and they were offered rehearsal space to start developing it. “A luxury that Ell and I have never had,” says Higgins. “We’re just always in my kitchen.” They’ll be working with Edwards again, this time from the start. “It feels like we can spread our wings.”

In the meantime, after their run at Soho, they will be performing Hotter at the Edinburgh Fringe’s Underbelly. They have plans to tour, but have yet to fulfil the dream of doing the show in schools. Higgins says people tell them: “I wish I’d seen this when I was 14, 15, 16 – it would have derailed a lot of shitty body stuff.” Looking forwards, there’s also potential for the show to change form, perhaps appearing as a podcast. “I think that’s the way for Hotter to grow up a bit,” adds Higgins.

So where do the pants fit in? As the characters they play unpeel layers of themselves, Higgins and Potter echo this with their clothing, all the way down to their newly printed pants. After hearing such a variety of fears and anxieties about bodies, this feels both celebratory and brave. Potter admits to finding it terrifying.

“But if you started with your clothes off,” Higgins says, “you’d be really self-conscious, because you’d be thinking they’re looking at you the way people look at posters and magazines and themselves in the mirror. But I feel like – well, the dream is – by the end of Hotter, you’re not being looked at like that. They’re just watching your joy.”

• Hotter is at Soho theatre, London, 11-15 June, then at White Belly at Underbelly, Edinburgh, 12-25 August.