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Why a rinse won’t do: on menstrual cups, bacteria, and toxic shock syndrome

A new study shows that menstrual cups and cotton tampons may not be as safe as people are being led to believe. Microbiologist Siouxsie Wiles explains.

Diva, Fleur, JuJu, Kiko, Lunette, Me Luna, Mooncup, My Cup, Sckoon, Tāti, Wā, Yuuki. All cutesy names for the same thing: the menstrual cup – a “cup” people insert into their vagina to collect blood during their period. Once the cup is full, it’s removed, emptied, given a rinse and popped back in.

I have to admit that the very idea of a menstrual cup completely freaks me out. I blame the many hours I spent either sitting in microbiology lectures as an undergraduate or teaching students about nasty microbes as a university lecturer. Because I now know far too much about the (admittedly very rare but pretty deadly) bacterial disease toxic shock syndrome, as well as the ability of the bacteria responsible to stick to things like menstrual cups. A new study just published by researchers in France has reinforced all my fears. It’s also a bit of an eye-opener for those of us who use tampons.

Periods and Toxic Shock Syndrome 101

Before I get into what the researchers have found, a brief intro to toxic shock syndrome, otherwise known as TSS. TSS is caused by the release of special toxins by the bacteria Staphylococcus aureus and Streptococcus pyogenes. The toxins are often referred to superantigens as they have this incredible ability to directly interact with important cells of our immune system, leading to what’s called a cytokine storm.

In Staphylococcal TSS this means that a normally healthy person begins to appear confused, becomes feverish, and develops a weird rash that looks like peeling sunburn. If untreated, within days they can end up in a coma, suffer multiple organ failure and die.

In the late 1970s a new super-tampon went on sale in the US, able to absorb nearly 20 times its weight in blood which meant it could be worn for several days. Cue an epidemic of Staphylococcal TSS and the discovery of the link between the disease and tampon-use.* Unsurprisingly, super-absorbent tampons were taken off the market. Now every box of tampons sold comes with a warning about TSS and the instruction that tampons should be changed every 4-8 hours.

To get Staphylococcal TSS you first need to have the toxin-producing form of S. aureus present in your vagina. Then the bacteria need to have the right conditions to grow and produce the toxin. Those conditions are more likely to happen if you wear a tampon for more than 8 hours. The good news is that while studies have shown that as many as half of healthy tampon-users have S. aureus living in their vagina, only very rarely is it the toxin-producing kind. Hence why Staphylococcal TSS is very rare.

Which brings me to menstrual cups, which are marketed as a cheap, safe, and environmentally-friendly alternative to tampons. I’ve also read several articles like this one, in which people say there is no risk of TSS from using menstrual cups. Turns out that’s not true at all.

Period in a bag

In this new study, the researchers tested a bunch of different brands of tampons and menstrual cups. They put each tampon or cup in a sterile bag and added a liquid that S. aureus likes to grow in.** Then they added some S. aureus that they know produces the toxic shock toxin (one hundred thousand colony forming units per mL, to be exact). Eight hours later the researchers measured how much the S. aureus had grown and how much toxin the bacteria had made. I’ve summarised their findings in the graph below. Basically, the higher the bar, the more bacteria, and the bigger the scary-looking toxic symbol, the more toxin produced.*** It’s worth keeping in mind that this is a lab-based study, so lots of things will be different in actual people, but I still think it’s worth paying attention to the findings.

What did they find?

On average, there were about 5-10 times more bacteria and more toxin with the menstrual cups than the tampons. But there were nearly a thousand times more bacteria and a hundred times more toxin for the worst menstrual cup compared to the best tampon.

For the tampons, there were huge differences between the brands. The worst performing tampon had a hundred times more bacteria than the best. This is probably due to what the different tampons are made of. Ironically, the worst tampons were from the brand made from 100% organic-certified cotton (because women shouldn’t be exposing their sensitive and absorptive parts to “pesticide residues, phthalates, azo-dyes and dioxins…”). Go figure.

The researchers also looked to see whether the bacteria had stuck to the tampons or cups. This isn’t important for tampons, which get thrown away after use. But it is super-important for cup-wearers. As I said earlier, the advice is to rinse after each use and sterilise at the end of a period.

To me, the most important finding of the paper is that S. aureus is able to stick to the menstrual cups. This means that a simple wipe/wash just isn’t good enough as people will just be putting a cup coated with bacteria back inside themselves. Menstrual cups should be sterilised**** after every use instead. They should probably also be emptied more frequently than is currently recommended.

So do I think this means we should ditch the menstrual cups? No. Putting aside their environmental impact, tampons are bloody expensive (pardon the pun). So-called “period poverty” is a real problem, with reports of many young people missing school because they can’t always afford sanitary products. Several fantastic initiatives have sprung up that give menstrual cups free to those who need them. What people need are more than one, and clear instructions on when and how to sterilise them.

As for me, I can afford to stick to using tampons, but I’ll definitely be ditching those made from 100% cotton.

Reference: Nonfoux, et al. Impact of currently marketed tampons and menstrual cups on Staphylococcus aureusgrowth and TSST-1 production in vitro. Applied and Environmental Microbiology. doi: 10.1128/AEM.00351-18

* Check out this video featuring US CDC researchers talking about how they unravelled the link between TSS and high-absorbency tampons.

** Brain Heart Infusion broth, if you are curious. I’m wondering why they didn’t use human blood.

*** What I don’t know is how much toxin is enough to make someone ill.

**** The same way baby bottles and teats are sterilised…. Though if you want something scientifically-proven to work against S. aureus, this paper suggests using shock-waves!


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