It takes around 28 days for the skin’s natural exfoliation cycle to finish, a process known as desquamation. While chemical exfoliants, like lactic acid, will aid the process, it still takes time.

So you been sprinting, Lily? Just a bit of cramp? So that's the lactic acid building up. When an athlete does too much or runs too vigorously, not enough oxygen can be delivered to the muscles.