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Effects of Humidity

Effects of Humidity

What happens to hair during periods of changing humidity?
How does human hair compare to that of other animals?
How do other materials compare in expansion and contraction?

Introduction: (Initial Observation)

Humidity has a significant effect on all of us, and on many things around us. A device measuring humidity is called a hygrometer.

In 1783, Swiss physicist and geologist, Horace Bénédict de Saussure built the first hygrometer using a human hair to measure humidity.

How can human hair be used to make a hygrometer?

I have noticed that some people’s hair will get curly in a humid air. Is it the principle behind a hair hygrometer?

In this project you will study to determine what happens to human hair as humidity changes?

How does human hair compare to that of other animals?

How does human hair compare with other material in expansion and contraction caused by humidity?


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Project plan:

It is good to have a project plan in writing before you start your investigation or your experiments. In your project plan write what are you planning to do for your project. Later as you progress in your plan, you may deem necessary to change, remove or add to your project plan. This is a sample project plan:

  1. Finding and collecting human hair (long strands), animal hair, and other long filaments (fibers) that may be tested for expansion and contraction in different humidity levels.
  2. Design and construct a device to measure the expansion and contraction of hair and other filaments.
  3. Devising a method to create high humidity and low humidity test environment.
  4. Testing the collected samples for their expansion and contraction in different humidity levels.

Information Gathering:

Find out about hair. Read books, magazines or ask professionals who might know in order to learn about the effect of humidity on hair. Keep track of where you got your information from.

Following are samples of information that you may find:

About Hair

Each hair on your body grows from a hair follicle, a tiny, saclike hole in your skin. At the bottom of each follicle is a cluster of special cells that reproduce to make new hair cells. The new cells that are produced are added on at the root of the hair, causing the hair to grow longer.

The living tissue that makes your hair grow is hidden inside the hair follicle. The shaft, the part of a hair that you see, is made of cells that aren’t living anymore. That’s important to know when you are messing with coloring or perming or straightening your hair. If you cut yourself, your skin can heal, since it’s living tissue. If you damage your hair, it can’t heal. You just have to do what little you can to repair the damage or cut the damaged hair off and wait for more hair to grow back.

Each hair shaft is made up of two or three layers: the cuticle, the cortex, and sometimes the medulla. The cuticle is the outermost layer. Made of flattened cells that overlap like the tiles on a terra-cotta roof, the cuticle protects the inside of the hair shaft from damage.

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.


What is a hygrometer?

A hygrometer is an instrument used to measure the moisture content or the humidity of air. Mechanical hygrometers use human hair to determine moisture content, based on the principle that organic substances ( human hair) contract and expand in response to the relative humidity. The contraction and expansion moves a needle gauge.

Other types of hygrometer:

The best known type of hygrometer is the “dry and wet-bulb psychrometer”, best described as two mercury thermometers, one with a wetted base, one with a dry base. The water from the wet base evaporates and absorbs heat causing the thermometer reading to drop. Using a calculation table, the reading from the dry thermometer and the reading drop from the wet thermometer are used to determine the relative humidity.

Resistance Hygrometer: A hygrometer that measures relative humidity directly, with an accuracy of ±10 percent. It exploits the property that the electrical resistance of certain materials, such as carbon black and lithium chloride, changes with variations in the relative humidity.

Balance Hygrometer: Leonardo da Vinci built the first balance hygrometer in the 1400s. His hygrometer is based on the principle that the weight of a hygroscopic substance (hair, oat-beard, and many animal and plant fibers) change when a variation in the amount of water in the air is recorded.

Francesco Folli invented a more practical hygrometer in 1664. Other scientists who invented or improved hygrometers are Robert Hooke and John Frederic Daniell. Daniel is best known for inventing the Daniell cell, an improvement over the voltaic cell used in the early history of battery development.

In 1783 Saussure built the first hygrometer utilizing a human hair to measure humidity. The hair hygrometer is an instrument that measures the humidity in the air (hygrometric grade). It was a type of instrument that was used widely in its time, although it was not very precise. All hair hygrometers can be considered as being derived from that of Horace-Benedict de Saussure. In this specimen, the hygrometer is inside a wooden case with a glass door, in which a mercury thermometer with a scale from -20°C to +35°C. The instrument can be hung on the wall with a hook.

How To Calibrate Your Hygrometer

How to calibrate your hygrometer (for use with cigar boxes).

  • Dampen a towel so it’s soaked but not dripping. Wrap it completely around your hygrometer.
  • Wait 30 to 40 minutes, unwrap, and quickly check your hygrometer reading. It should read 98% or higher.
  • If it does, you’re done and your hygrometer is correctly calibrated.
  • If it doesn’t, then turn the screw in the back of the hygrometer until the reading is 98% or greater. You’ve successfully calibrated your hygrometer and you can return it to the humidor. You should calibrate it again in about a year.
  • If you don’t want to fiddle with the screw on the back of your hygrometer, then simply make a mental note about how far off your hygrometer was. Say after the towel, your device read 80%. You know it’s about 20% off.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to determine how do different materials (such as human hair and other natural or synthetic fibers) contract (shorten) or expand (lengthen) with changes of humidity.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the type of natural or synthetic fiber. Possible values are blond hair, black hair, synthetic hair, nylon filament, silk, rayon.
You may have access to other synthetic or natural fibers that you may want to include them in your study. You may also reduce the number of variables to hair and one more fiber.

Dependent variable (also known as responding variable) is the rate of expansion or contraction by changes in the humidity.

Controlled variables are light and temperature. (perform your experiments at room temperature)

Constants are the experiment method and procedures.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

This is a sample hypothesis:

Among our test fibers, human hair will have the highest rate of expansion and contraction by changes in humidity. My hypothesis is based on my gathered information about the history of using human hair in construction of hygrometers.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Introduction: In this activity, we’ll hook up a long hair to a lever system and create a hair hygrometer that can measure changes in humidity. We will use this device to measure the rate of expansion or contraction of hair. We will later repeat this experiment with other types of natural or synthetic fibers.

You’ll need these materials:

  • Back plane or column: A scrap piece of wood, cardboard or foam board (about 30 cm long and 8 cm wide).
  • Pointer: A flat piece of plastic (21 cm long and 2 cm wide) thin enough that you can cut or sheet of balsa wood.
  • Straight wire (optional, for wire pointer)
  • 2 small nails or screws
  • Long strands of human hair and other fibers (about 30 cm long)
  • glue
  • tape
  • hammer
  • scissors (strong enough to cut plastic)


Cut the piece of plastic to make a pointer as shown in the following diagram. The pointer will have two holes named hair hole and nail hole. Hair hole is exactly 18 cm away from the tip of the pointer. Nail hole is exactly 20 cm away from the tip of the pointer.

Straight wires (known as stem wires available at craft stores and flower shops) may also be used to construct a pointer. Simply use a small needle-nose pliers to bend the wire and make two loops. The nail loop is 20 centimeters away from the tip of the pointer. The hair loop is 18 centimeters away from the tip of the pointer.

Your back plane can be a flat board or an L shaped structure as shown in the diagram below. Place the pointer on the back plane and insert a nail through the nail hole into the back plane. Needle should be able to freely move up and down.

Get a strand of blond hair about 50 centimeters (2 feet) long. Insert one end of the hair into the hair hole and secure it there with a knot or by adhesive tape.

Secure the other end of the hair as high as possible on the column or back plane using a knot on a nail, or a push pin or adhesive tape. Make sure that at this time the pointer stands horizontally.

Place a card board behind the pointer where you can mark the position of the pointer in different humidity conditions.

At this time your hygrometer is ready, so you can start measuring the changes in the length of hair caused by changes of humidity.

Place a plate filled with a dehumidifier substance such as lime (Calcium Oxide) in the box and close it for about 10 minutes. Then open the box and immediately mark the cardboard where the pointer is positioned. This will be the dry mark.

Place your device in a box or cabinet at room temperature. Fill up a cup* with hot boiling water and place it in the box next to the hygrometer and close the box door. The vapors from the hot water will increase the humidity inside the box. After 5 minutes, open the box and mark the cardboard where the pointer is positioned. This will be the humid mark.

* Some believe that a cup of hot water does not provide enough humidity. They suggest to use a humidifier or hang wet towels around the device.

Measure and record the distance between the dry mark and the humid mark. Divide this number by 10 to get the actual length change on your hair sample.

The hair hole in your pointer is positioned where the tip of the pointer will move 10 times more than the hair hole itself.

Divide the length change of the hair by the length of hair between the two points to calculate the rate of expansion (or contraction) of the hair.

Repeat your experiments a few times of blond hair, black hair, synthetic hair and other natural or synthetic fibers that you like to test.

Additional Tips:

If your pointer is very light and cannot keep the hair sample stretched, you may need to hang a paper clip or a dime to the middle of the pointer to make it heavier.

You may use a single strand of hair or you may use multiple hair strands placed side by side. Pull the hair strands straight and tight so that the pointer points parallel to the ground. That is, make sure the point of the pointer is perpendicular to the hair. The hair should hang is vertical as possible.

As a dehumidifier you can fill up a metal can or a plastic bag with crushed ice and salt. Place the can or the bag on the plate in your box. The super cold temperature of ice and salt mixture will condense the moisture in the box. Condensations will be collected in the plate.

You may have a results table like this:

Fiber/ Filament Length Changes in length Percent of length change
Blond Hair
Black hair
Synthetic hair

Materials and Equipment:

List of material may be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


No calculations is required.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

The human hair cells will indicate the level of moisture in the air by expanding and contracting. When the air is moist, the hair will expand and lengthen, making the pointer point down. When the air is dry, the hair will contract and shorten, making the pointer point up.

As the relative humidity increases, hair becomes longer, and as the humidity drops it becomes shorter. On very humid days, your hair actually becomes longer and this extra length causes the curl or fuzziness that gives us bad hair days.

From dry to humid, hair length can change by 3 percent. How do other fibers change length by changes in humidity?

Why does human hair expand by humidity or moisture?

Hair is composed of protein, not too unlike the protein of an egg (the white part). When the air is humid, then more water can surround the hair protein (or be absorbed in the hair protein) causing it to stretch as it begins to weigh more. Also, extra water from sweat (from the humidity) helps to stretch the hair even more! Of course, not all hair is the same! Some hair is curly. With some people, the extra water from the humidity may cause the hair to become more curly. But even then, after a while, the hair becomes more soaked with water and begins to stretch after more water absorbed.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List of References


Sample Abstract

Does Hair Type Affect Hair Hygrometer Results?

The purpose of this project was to find out which type of hair responds quicker to a hair hygrometer. A hair hygrometer is an instrument used to find the humidity in the air.

The main structures of the hygrometer were built. Next the hairs had to be connected (that have already been boiled for five minutes) to the nails and to the arrow. It would point to wet or dry depending on what stage of the procedure it was on. I then tested the hair in the chamber (Tupperware) with two cups of water. I waited for the humidity to rise for thirty minutes and to move the arrow to the wet mark on the face of the hygrometer. Next, I took out the water, dried the chamber, and then added half a cup of calcium sulphate (a.k.a. desiccant). At this time I started my stopwatch. The desiccant was used to absorb the moisture and dry the hair, which would move the arrow to the dry mark on the face of the hygrometer.
This was the drying time or response time.

It was found that all of the non-dyed hair samples dried out at an average of 22 minutes 18 seconds. The dyed hair samples dried out at an average of 41 minutes 15 seconds.

The hypothesis was incorrect. It was believed that the dyed hair would dry faster. The dyed hairs took longer to dry because they absorbed more water than the non-dyed hairs.
There were a few problems. A hygrometer was broken. The procedure needed sunlight and the project was tested during the winter months so I ran out of light on several occasions.
I learned that the process of dying hair may dry it out.
I will isolate natural hair color to determine if color is a factor in dry time.