Pregnancy is the most common reason for a missed period, but it isn't the only reason. In this video, SciShow explains a few other reasons you might skip a period.
Tagged With menstruation
The theory that close friends have their periods at the same time is over 40 years old now, but there has never been much evidence to support it. The people behind the period tracker Clue checked their own data recently and came up with another nail in the coffin: Zero evidence that closeness makes people bleed in sync.