By Siouxsie Wiles 29/04/2018

Last week a new lab-based study came out, about menstrual cups, tampons, and toxic shock syndrome (1). In this post, microbiologist Siouxsie Wiles reflects on the various responses she’s had to her blog about the study. 

If you need reminding, toxic shock syndrome is one of the bogey-men every menstruating teen is warned about – a very rare complication of a bacterial infection that can quickly result in organ failure and death. Journalists were soon calling me, asking what the study meant. They all wanted to know, are menstrual cups more dangerous than tampons? As usual, the answer was a little more complicated than a simple yes or no.

As a microbiologist, one of the main conclusions I drew from the study was that people who use menstrual cups would be better off cleaning them more rigorously and more often than they are being advised to. That’s because the study showed that the bacteria that can cause toxic shock syndrome are able to stick to menstrual cups, so a quick wash or rinse won’t be enough to dislodge them. This finding didn’t come as a surprise to me, as bacteria sticking to things we put into people’s bodies is a well-known thing. It’s a massive cause of infections in people who have to be catheterised, or ventilated, amongst other things. As an aside, loads of researchers are trying to develop materials can’t stick to, or that kill any bacteria that do stick.

What the study findings suggest is that over the course of a period you could be putting a cup that’s becoming more and more covered in potentially harmful bacteria back inside your vagina. So, that’s what I told the journalists and also wrote about (my post appeared here and here). Yes, toxic shock syndrome is very rare, but isn’t it better to sterilise and be safe than sorry?

It’s been great to see the resulting discussions on social media from menstrual cups users. Unsurprisingly, they’ve been asking lots of questions about how to sterilise their cups. I clearly shouldn’t have relegated that info to a footnote! That footnote was an educated guess – basically, the same way people sterilise baby bottles and teats should suffice. I haven’t been able to find any published studies that specifically address the issue. It doesn’t look like anyone has done the experiments, or if they have, they haven’t published their findings. If you think that’s not good enough and want to help us study it, then I went to hear from you. Go here.

No, I’m not in the pay of Big Tampon…

What I’ve been absolutely blown away by are the responses from menstrual cup users who seem offended by both the original study and my posts, and my advice to sterilise cups more often. I know, I know, never read the comments… The most ridiculous criticism is that somehow this is all an attack on those who want a more environmentally-friendly solution to periods. That we’re in the pay of the tampon industry. Seriously?! Researching nasty bacteria is my thing. My funding mostly comes from the New Zealand government, members of the public and a super charity called Cure Kids. With that money, we’re trying to understand how some bacteria are infectious. With the rest of it were looking for new antibiotics because antibiotic-resistant bacteria are scary as hell and could bring about the end of modern medicine pretty soon. Don’t believe me? Read my book.

No, you aren’t more at risk not using sanitary products…

Some people seem to be accusing me of misrepresenting and overblowing the results of the study. I’ve written a response here about what that study can and can’t tell us about menstrual cups and toxic shock syndrome. I also want to apologise for not clearly explaining one of the results of that study, which seems to have confused some people. In the graph, there is a column that shows that the bacteria grow really well (and in many cases, better [there are lots of reasons for this but I don’t have space to go into it here]) without tampons or menstrual cups. That’s what’s known as a positive control and just shows that the bacteria are behaving as they should in lab-based conditions. That data doesn’t show that you are MORE at risk if you don’t use any sanitary products at all. It also doesn’t mean the risk of getting toxic shock syndrome from using tampons or cups is the same as using nothing at all.

One of the things people are using as evidence that I’ve overblown the results of the study is that there have only been a couple of documented cases of toxic shock syndrome related to using menstrual cups. Does that mean those have been the only cases? No. There could easily have been others that haven’t been reported. Even if that is the real number, it might just be because menstrual cup users are in the minority and not all strains of the S. aureus bacterium carry the toxin gene. What happens as cup use becomes more widespread, or if the toxin-producing bacteria becomes more common? Over the last few years, the dominant strain of S. aureus in New Zealand has changed as a result of our use of antibiotic-producing creams. We’re just lucky the new dominant strain is one that doesn’t have the toxin gene.

Where are all the menstrual cup studies?!

In reality, there are loads of things we still don’t know about using menstrual cups. That’s because, like most other issues that relate to women, it’s hardly been studied at all. I counted 14 relevant studies on the journal article database Pubmed. There’s this new study, an older similar lab-based study, three case studies reporting bad outcomes in women using a menstrual cup, and 9 reports of actual clinical trials. Of those 9 clinical trials, one is about a single-use disposable menstrual cup, one was an interview with women to see if they would use a menstrual cup, and three gave just a few hundred women a questionnaire after wearing their cup to ask about comfort and leakage. As far as I can tell, there are just four papers about actual clinical trials, two of which relate to the same study of about 700 Kenyan school girls followed over 11 months, another following 47 Canadian women for 4 menstrual cycles, and another that followed 10 women for 72 hours. There are another 4 papers, but they date back to the late 50’s and early 60’s and I couldn’t find abstracts for them so I’ve no idea if they were case studies, trials or opinion pieces.

So, it looks we’re making judgements about the safety of menstrual cups based on the study of their use in less than 800 women and young girls. And only the Kenyan study looked specifically at vaginal colonisation by S. aureus (2 girls came back positive for toxin-carrying S. aureus), and whether there were any instances of toxic shock syndrome (2). There weren’t any, but that’s hardly surprising. If the incidence was the same as seen in tampon-users then they would have needed more than 25,000 people in the trial to have a chance of seeing one case of toxic shock syndrome. Incidentally, that study also took 30 used cups to see if they had the bacterium Escherichia coli stuck to them. 13 cups did. Again, bacteria like to stick to stuff.

If you are as appalled as I am at how little this has actually been studied and want to help me change that, then read my post here. Let’s fix this!


  1. Nonfoux, et al. Impact of currently marketed tampons and menstrual cups on Staphylococcus aureus growth and TSST-1 production in vitro. Applied and Environmental Microbiology. doi: 10.1128/AEM.00351-18
  2.  Juma, et al (2017). Examining the safety of menstrual cups among rural primary school girls in western Kenya: observational studies nested in a randomised controlled feasibility study. BMJ Open. 7(4):e015429. doi: 10.1136/bmjopen-2016-015429.