Twenty billion disposable menstrual products are discarded each year in the US. There's a huge array of reusable options, from pads to pants to menstrual cups. Ana Santi explores which is the most sustainable and how safe they are.

During a weekend away with my girlfriends a few years ago, one of them mentioned that she was wearing period pants, an environmental decision to move away from single-use pads and tampons. I'd vaguely heard of them, but didn't know anyone who wore them and I'd always been a little sceptical – would they be absorbent enough? My friend convinced me otherwise and they've remained my product of choice ever since. But as I browse the shelves of menstrual products in my local supermarket today, I'm overwhelmed by the choice available: so many pads and tampons (some organic, most not), numerous types of cups, a few period pants.

And still, 49 billion single-use period products are used every year in Europe alone. In the US, it's about 20 billion discarded each year, generating 240,000 tonnes of solid waste. Globally, disposable sanitary pads – which can contain up to 90% plastic and end up largely in landfill – are the most commonly used menstrual product.

I set out to find the most sustainable period product available.

Given that 1.8 billion people across the world menstruate every month, a group of academics based in France and the US conducted a life-cycle assessment of menstrual products across four product groups: disposable non-organic and organic pads and tampons (with applicators); reusable pads; period underwear; and menstrual cups, which are made from soft, flexible silicone or rubber and can hold 20-30ml (around two tablespoons) of menstrual blood. Comparing eight environmental impact indicators – global warming potential, fossil resources, land use, water use, carcinogenic effects, ecotoxicity, acidification and eutrophication – and conducted over one year across three countries (France, India and the US), the assessment considers impacts from production to disposal.

Across all the three countries and environmental impacts, the menstrual cup was a clear winner, followed by period underwear, reusable pads and, in last place, single-use pads and tampons. Small and lightweight, one person's menstrual cup can last up to 10 years.

Disposable pads – both organic and non-organic – had the highest impacts across all eight categories except water use, with non-organic pads scoring the highest for global warming potential and resource depletion. The global warming potential – greenhouse gas emissions' ability to absorb heat and warm the atmosphere over a given time period – came from manufacturing, with almost half of the impact from production of polyethylene (a petroleum-based plastic). But one of the most surprising results – not least to the report's authors – was that organic cotton pads had the highest impact of all, across five categories.

"The impacts are mostly linked to raw material manufacturing and organic production, which can have higher environmental impacts," explains Mélanie Douziech, one of the study's co-authors from Mines Paris-PSL university. The yield of organic farming is lower than conventional farming, meaning more water and land is needed to produce the same amount of organic as conventional cotton. Similar results were found for organic and non-organic cotton tampons.

Depending on the product, different parts of the lifecycle influence the emissions. "For disposable products, it's the raw material production and manufacturing, as a lot of these products have plastics in them, which have quite a large global warming impact," says Douziech. "With reusable products, it is the manufacturing and use phases, especially the electricity requirements."

Water and electricity are needed to wash all reusable products between wear, but period pants perform better than reusable pads, in part because otherwise........

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