Tampons are usually very safe, however, around 1 in 100,000 menstruating people will be affected by TSS each year. It is still not well understood why menstruation and tampon use can contribute to the development of TSS but there are several theories.
Firstly, since the acidity of the vagina is lower during menstruation, it may be more hospitable to the growth of Staphylococcus bacteria, thus increasing the risk of TSS. Tampons may also introduce oxygen into the vagina and provide an ideal growing environment for bacteria, especially products containing since-banned synthetic materials.
Another issue with tampons is fibre shedding. Many brands of tampons contain hidden plastics and researchers at Middlesex University recently discovered that a typical tampon releases 9.4 billion nanoplastic fibres during use. Although cotton tampons are likely to shed fewer fibres, all types can build up in the vagina and lead to an increased risk of infection. Some brands, including Grace & Green, have a protective outer layer which prevents fibre loss and therefore reduces the risk.
Whilst tampons are the most common factor in menstrual-related cases of TSS, anything you put into your body is a potential risk. For example, there have been several reports of TSS from use of menstrual cups and some contraceptive devices such as diaphragms and IUDs.