None of these beliefs are correct. Periods are natural and normal for women. Menstrual fluid is just a harmless mixture of blood and tissue that was not used by your body to nourish a baby in the Womb.

This myth is often used as a reason to stop women, who are having their periods, from taking part in various social events. This happens especially in the case of religious events.

Illustration of a menstruating woman experiencing pain due to cramps while in the shadow she looks like a demon to depict the menstrual myth that menstruating women are cursed - Menstrupedia