cortisol

Cortisol is a steroid hormone produced by the adrenal cortex, the outer layer of the adrenal glands that sit atop the kidneys. In Latin, cortex means 'bark' or 'rind'—the outer layer of a tree, or by extension, the outer layer of any organ. Edward Kendall and his team at the Mayo Clinic isolated the hormone in the 1930s and began to understand its role in metabolism and stress response.

In 1949, Kendall and two colleagues won the Nobel Prize in Physiology or Medicine for discovering the hormones of the adrenal cortex and their therapeutic applications. The hormone needed a name. They combined cortex (the organ) with -ol, a standard suffix for alcohols and organic compounds. Cortisol: the oil from the cortex.

The word itself is technical and chemical—invisible to most people. But the hormone is famous. It spikes when you're stressed, suppresses immune function, raises blood sugar, and narrows your attention to immediate threats. It's the hormone of fight-or-flight, the first responder to danger or simply to the sensation that something is wrong.

Now cortisol is measured, tracked, blamed for weight gain and fatigue. People talk about 'cortisol levels' as casually as they talk about weather. The hormone that Kendall discovered as a pure scientific curiosity became a stand-in for modern stress itself. We still don't fully understand it, but we can't stop talking about it.