Reusable menstrual cups are less wasteful and costly than disposable pads and tampons, but they’re inconvenient. Removing one can be messy if menstrual blood spills, and they must be sanitized between uses.

Those issues are preventing their wider adoption, according to researchers at McMaster University in Hamilton, Ontario, Canada, who’ve engineered an improvement: an absorbent tablet to be placed inside an antibacterial-coated menstrual cup. Their new design prevents spillage and the need for harsh sanitization, according to new research published in ACS Applied Materials and Interfaces.

This advance builds on growing research aimed at improving menstrual products’ sustainability, safety, and accessibility. The average menstruating person uses about 10,000 mostly plastic period products in their lifetime, most of which end up in landfills. Numerous tampon brands contain metals, including lead. Meanwhile, an estimated 500 million people globally lack access to period products.

However, an emerging generation of products is addressing the challenges that scientists and manufacturers have long neglected.

Tampons and pads haven’t changed much “for decades,” said Zeinab Hosseinidoust, PhD, lead author of the study and associate professor of chemical engineering at McMaster University. But more recently, she’s observed “movement toward reimagining what can be done, both from a sanitary and monitoring perspective.”

Creating an Absorptive Tablet

The Bfree Cup, an antibacterial silicone menstrual cup, has been available in Uganda and Canada since 2021. Women’s Global Health Innovations, the company behind the cup, wanted help making it less messy to use and approached Hosseinidoust and Co-author Tohid Didar, PhD, a few years ago. The idea of a tablet began to take shape.

"That’s when we started looking into these algae-based gels. We wanted something that you can flush down the toilet,” said Didar, associate professor of mechanical engineering at McMaster University.

The researchers had experience with biodegradable hydrogels, which are flexible and very absorptive. They also had ongoing projects using alginate, a brown algae product that’s cheap and widely available.

To make the tablets, they spun alginate hydrogels into fibers interwoven with calcium chloride, an inorganic salt. They compressed the fibers before die-cutting them into teardrop shapes to fit into menstrual cups. The tablets capture and hold menstrual fluid by causing it to clot and solidify.

In a petri dish, a 1-g tablet absorbed 15 mL (the capacity of a menstrual cup) of blood over 8 hours. It took 4 days to dissolve in a water-based salt solution, whereas disposable menstrual pads can take from 500 to 800 years to break down. They also tested three menstrual cups for antibacterial effectiveness. Only one cup had been manufactured with an antibacterial coating. They developed a similar coating that significantly reduced biological material sticking to the two other cups.

Next, the researchers plan to conduct a study with participants using the cups and tablets. They’ll also be exploring mass production of the alginate fibers and testing the flushability of liquid-soaked tablets.

Other Innovations in Period Products

In addition to the absorptive tablets developed by researchers at McMaster University, a number of other sources are working to make menstruation easier to manage and more eco-friendly:

• Joii, a new app developed in Ireland, measures period volume and clot size, potentially identifying flow changes or problems early.
• In 2023, Stanford researchers developed an absorbent pad material from sisal, a widely cultivated plant in regions lacking period products, in the hope of encouraging sustainable local manufacturing.
• In 2018, British period product maker Callaly created an organic, more than 95% biodegradable cross between a tampon and liner to prevent leaks.

“People are realizing that this is a gold mine for health, for research, or for commercialization because it’s an untouched area,” Hosseinidoust said.

Moreover, a younger generation that includes her students has demanded sustainable, convenient, and health-promoting period products. “They didn’t grow up with the same taboos that I did,” she said.

Those stigmas have also affected scientists, according to Jenni A. Shearston, PhD, environmental epidemiologist and public health researcher at the University of Colorado Boulder.

“I think the taboos around menstruation impact what scientists choose to ask. If it never occurs to us to think about scientific questions related to menstruation, we don’t ask them,” she said.

During her PhD at the University of California, Berkeley, Shearston studied period products’ toxicity, leading to her co-authoring the 2024 study of metals in tampons — the first-ever investigation of the issue.

Her team at the University of Colorado is currently investigating how different metals and concentrations might affect vaginal tissue and the rest of the body.

“Finding a chemical in the menstrual product doesn’t mean that the chemical comes out of the product or that the chemical gets into our bodies. We don’t know that part,” Shearston said.

Looking beyond their work with reusable menstrual cups, Didar and Hosseinidoust want to find a way to detect elevated Escherichia coli — a possible marker for endometriosis — and help diagnose ovarian cancer early using period products.

“It’s something that people have 6, 7 days a month,” Didar said. “That’s the perfect opportunity for someone to know what’s going on without going to the doctor.”