Hair vs. Humidity; Does Hair Shorten When it is Humid?

Hygrometers measure relative humidity.

How many times have you said, “I can’t do a thing with my hair”? Summer humidity in the southeast is no friend to your hairdo. It can puff, fluff, curl and go crazy. Does hair get get shorter or longer when humidity rises? Here’s Chief Meteorologist Alan Sealls with an experiment to answer that age-old question.

I started my experiment with an email survey. Most News 5 staffers said hair gets shorter when relative humidity increases. So I enlisted the help of summer intern Jesse Kelley. He’s a meteorology major at the University of South Alabama. We designed a hygrometer- that’s an instrument to measure relative humidity but we needed one more thing that neither of us has- long hair! Enter Avery Cotton and Ashley Knight. Avery agreed to donate a few locks for the advancement of science. Ashley did the easy part. The hardest part was trying to tie a single strand of hair to a nail and to a pointer. Once that was done, I labeled the giant hygrometer so that if the hair shortened, it would rise. If the hair lengthened, it would fall. We went outside. Jesse took humidity readings . After a while outside- no change. The relative humidity was not very high. So I put the hygrometer in the men’s shower and waited. Still, no change. The air conditioner kept lowering the relative humidity.

Day 2. We took the instrument outside again. No luck. The midday relative humidity was a lot lower than it was in early morning.

Finally. Day 3, we got the rain and very high relative humidity right afterward. The result was not dramatic but the pointer showed a longer hair with higher relative humidity. So the answer to the question is when air is more humid, your hair gets a little longer.

The most that hair changes length is only about 3%, but it’s not perfectly 3% for the whole strand and that’s why some hair curls. Human hair has been used in professional hygrometers since the 18th century because it responds to relative humidity. Horse hair and other animal hair works pretty well too. Here’s a view of a recording hygrometer, also known as a hygrograph.

The survey shows that just because a lot of people believe something to be true, that doesn’t always make it true! One news 5 staffer got the answer right. Note this was not a perfect experiment. I used a wooden pointer which may have warped and given a bad reading. Similarly, the wooden base of my hygrometer may have expanded or contracted slightly with humidity. Finally, I never asked Avery, but if her hair had conditioner, spray, or gel on it, then that would have also thrown off the results.

Here’s more on the science of how hair responds to humidity.

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