In early Buddhism, there are no menstrual taboos. Menstruation is seen as a natural physical excretion that women have to go through on a monthly basis.
Buddhists consider menstruation as a natural and vital biological process that isn’t associated with stigmas or taboos. Therefore, praying and meditating while on your period is allowed. There are no forbidden activities for menstruating women and ‘impurity’ is considered superstition.
Because they can get pregnant and give birth, but also due to menstruation and hormonal influences, women are considered closer to feeling spiritual and internal energy. This was believed by Garab Dorjé and Padmasambhava, about 1500 years ago. Those two gurus considered the female body, especially the womb and vagina, as place where all existence starts. During menstruation, women were thought to be more powerful and in touch with their energy.
However, Hindu beliefs have carried over into Buddhism so that nowadays there are certain taboos in Buddhist countries. In Taiwan and Japan, for example, women are not allowed to enter temples when they’re on their period. There’s also the folk belief that ghosts eat blood and that menstruating women would be a threat to themselves and others by attracting those ghosts.