Every woman carries two entirely separate sweat systems beneath her skin, and they behave nothing alike. One is a plain cooling mechanism that keeps the body from overheating. The other is a slower, richer, more curious system that clusters in only a handful of places — the underarms, the area…

Every woman carries a small, self-regulating laboratory that she never has to think about. It measures its own acidity, adjusts its own chemistry, and maintains a setting so specific that scientists can express it as a single number.