Better Hair Through Chemistry

  TRY THIS! by Paul Doherty and Linda Shore

Hair Hygrometer

Ever notice that when it’s humid you have a Bad Hair Day? Hair increases its length when humidity increases. So curly hair frizzes and straight hair goes limp. From dry to humid, hair length can change by 3 percent.

In this activity, we’ll hook up a hair to a lever system and create a hair hygrometer to measure changes in humidity. Invented in 1783, the hair hygrometer was so reliable that it was not replaced by an electrical instrument until the 1960s.



  • Corrugated cardboard about a foot long and 9 inches wide
  • A piece of thin cardboard
  • A pair of scissors
  • A knife
  • A pushpin or other large-diameter pin
  • A straight or common pin
  • A strand of hair that's one foot long
  • A hot glue gun
  • A dime
How-To Diagram
To Do and Notice
1. On the top edge of the corrugated cardboard, cut two slits about 1/4 inch apart and 1 inch from the left side.
2. From a piece of thin cardboard, cut out a triangular pointer about 6 inches long.
3. Cut two slits along the bottom of the pointer about 1 inch from the left edge.
4. Attach the pointer to the base with a pushpin 1/2 inch from the left edge in the center. Then take the hair strand and slide it through the top two and bottom two slits.
5. Hot glue the hair in place in both sets of slits, then hot glue a dime 1 1/2 inches from the left edge of the pointer base.
6. Push a pin through the hole in the pointer so that the hair is slightly stretched when the pointer is horizontal.
7. Calibrate your hair hygrometer at 100 percent humidity by bringing it into the bathroom when you shower. Make a mark when the pointer stops. Then use a hair dryer to dry the hair and make a mark for 0 percent humidity.
8. Monitor the changing position of your pointer as the humidity changes.

What's Going On?
Hair is made from keratin, a protein that is wound into a coil. The turns of the coil are held together by a type of chemical bond called a hydrogen bond. Hydrogen bonds break in the presence of water, allowing the coil to stretch and the hair to lengthen. The bonds re-form when the hair dries, which allows people to style their hair simply by wetting it, shaping it, then drying it.

The Healthy Hair Test

A strand of hair

To Do and Notice
1. Wrap the strand of hair around your forefingers so that your fingers are about an inch apart.
2. Pull the hair slowly, but firmly.
3. Can you feel the hair stretching out?

What's Going On?

Healthy head hair will stretch when you pull on it. That's because the cortex of healthy hair is strong and elastic. The cortex inside of a damaged hair strand is weak and brittle. It will break more easily when you pull on it.

Creating Curls

A strand of straight hair

To Do and Notice
1. Hold up a single strand of hair. Pinch the hair between the fingernail of your thumb and the fleshy part of your forefinger.
2. Run your fingernail across the hair strand. Try not to break the hair in two. If you do, get another hair and try again. Did your hair curl? If not, try again. Be patient; you'll get the hang of it.

What's Going On?
Okay, so this might not be the most efficient way to style your hair. But this activity wouldn't be possible if it weren't for the way the cuticle of a hair is structured. Your cuticle is made of overlapping cells arranged like the tiles on a terra-cotta roof. When you run your fingernails across a hair strand, you pull apart the overlapping cells on one side of the cuticle more than you pull apart the cells on the opposite side. The result: a tiny hair that kinks, twists, and curls.

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