Spot the difference
Exercise increases circulation, which can keep skin clear. But for women, running so much that it interferes with your period (amenorrhea) can trigger acne, explains Hale, because the hormonal balance shifts (more of the male hormone androgen, less oestrogen).
And for many runners, male and female, acne happens when bacteria naturally present on the skin gets trapped in pores by sebum and sweat. Folliculitis, another form of acne, is caused by the same combo that in this case infects hair follicles, causing a crop of red bumps.
Protect yourself: If your menstrual cycle is disrupted, visit your doctor: you may be low on oestrogen and potentially endangering your bones. To keep the skin generally spot-free, "if you're unable to wash right away, use wipes, or at least change clothes," says Hale.