Approximately every four weeks, skin regenerates itself, with new growth in the epidermis pushing up older cells primed for exfoliation. Working alongside that time frame is the menstrual cycle, a process that sees oestrogen, progesterone, and testosterone levels fluctuate, causing a variety of different effects on skin. The four phases of a menstrual cycle are the menstrual phase, follicular phase, ovulation, and luteal phase, and each bring their own skin changes.