In the 1970s, a combination of new synthetic materials and huge market competition led to an arms race among tampon manufacturers. There was a drive to be the most absorbent, the most leak-proof. Rely tampons, manufactured by Procter & Gamble, were highly absorbent, and expanded wide to prevent leaks. They quickly became a market leader owing to the innovative design and super absorbency.

Meanwhile, in the late 1970s, something else happened: a new syndrome was identified and named. Paediatrician James K. Todd reported an illness among childen aged 8-17. The childen had developed a condition after infection with Staphylococcus Aureus. He suspected toxins caused by the bacteria. He called the disease Toxic Shock Syndrome (TSS)

Once TSS was named and described, physicians across the USA began to notice it. And they spotted something unusual: the vast majority of cases were recorded in women, and onset of symptoms tended to take place within a few days of their periods.

An investigation was launched in 1980, and identified that menstruation-related TSS was caused by tampons. And a September 1980 report by the CDC identified that up to 75% of these cases were caused by one specific brand of tampon: Rely.

The thing about Rely brand tampons is that the manufacturers had inadvertently designed the perfect medium for helping S. aureus proliferate, and get its toxins into the bloodstream. A number of factors contributed to this.

An important thing to know about S. aureus is that it is frequently found in the vagina in small quantities. This isn't an infection, per se. The population is kept in check by the vaginal microbiome, and it lives there reasonably harmlessly. However, something very absorbent going into the vagina can shift the balance of the natural moisture of the vagina, which affects vaginal flora.

Rely brand tampons were *incredibly* absorbent. They could reportedly hold 20 times their own weight in fluid. They also had a unique design which essentially prevented anything getting out of the vagina while wearing it. (image from Rely's own leaflet)

The high absorbency of Rely tampons dried the vagina out fairly comprehensively, and due to dryness and the girth and flared tip of the tampons when expanded, this caused small abrasions in the vaginal walls - the perfect entrance for toxins produced by S. aureus to get into the bloodstream.

In addition, Rely's unique design consisted of a gel-like substance called carboxymethylcellulose and beads of polyester. It later turned out that the gel-like substance acted like a plate of agar jelly for S. aureus to grow, and the beads provided increased surface area for bacterial growth.

@vagina_museum Oh god... I can't imagine how bad keeping the same tampon for 24 hours must feel, and I don't even have a vagina!