Behind the Forecast: The hair-raising truth about humidity

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Science Behind the Forecast 3/15/19

LOUISVILLE, KY (WAVE) - Humidity. It can be bane of a cute hairstyle’s existence. One minute a hairdo is sleek, the next a giant frizz ball. At the root of it all... hydrogen.

Our hair is comprised of quite a few layers. The middle layer is made up of bundles of keratin, a protein that helps each strand keep its particular shape and structure. The keratin can be chemically bonded in two ways, through a disulfide bond or a hydrogen bond. A disulfide bond, two sulfur atoms bonded together, is more robust and is the key to hair's strength. Disulfide bonds are not affected by humidity.

Bundles of keratin proteins make up a hair shaft.
Bundles of keratin proteins make up a hair shaft. (Source: Gray’s Anatomy/ Smithsonian Mag)

Hydrogen bonds are weaker and much more finicky, breaking and reforming each time hair gets wet. Since hair is porous, it sucks in extra moisture from the air. These bonds connect strands of keratin by forming a weak attraction within a water molecule, which is made up of hydrogen atoms and one oxygen atom. Since warmer air can hold much more water vapor than cool air, strands of keratin create even more hydrogen bonds between themselves on those warm, humid days. This actually causes the strand of hair to more quickly fold back on itself on the molecular level, according to Smithsonian. The hair folds even more as the strands of keratin create more bonds with hydrogen, basically swelling then disrupting the air’s cuticle, the smooth outer layer. As it folds, we notice hair becoming much more frizzy.


Hair is so good at reacting to humidity that it’s actually used in meteorological tools called hygrometers. The higher the humidity, the more hair in the hygrometer shrinks.

To avoid bad hair days, experts recommend using serums and oil spray’s that create a barrier between your hair and the humid air. Those with drier, color damaged and even heat damaged hair are more likely to deal with frizz.

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