Culture and menstruation the ideal of synchronised tidal, lunar, menstrual and seasonal periodicities whose overall harmony (it is believed) confers spiritual power and fertility. To many, such cultural associations appear persuasive in view of the fact that in humans, the menstrual cycle quite closely approximates the moon's 29.5-day synodic cycle, unlike in chimpanzees (~36 days) or bonobos (~40 days). Statistical information from hunter gatherers is lacking, but where large-scale western studies focus on women's peak reproductive years—removing outlier values—the cycle length gravitates around 29.1–29.5 days, while the figure for women in their thirties shortens toward 28 days. In no extant human population has
Menstrual cup capable of growing on menstrual cups. However, there have only been two confirmed cases of toxic shock syndrome (TSS) associated with the use of the menstrual cups. The first case was a woman who had a history of Hashimoto’s thyroiditis and chronic menorrhagia. In the second case, the menstrual cup had been left in for 7 days. Menstrual cups are generally bell-shaped, with a few exceptions. Most brands use medical grade silicone as the material for the menstrual cup, although latex and thermoplastic elastomer are also options. Menstrual cups made from silicone are generally designed to last for 1–5 years.