There is no other part of the human body that reacts so obviously to water than hair.

When saturated, a strand of human hair can hold nearly a third of its weight in water and swell by up to 15% of its original thickness. Then, as the water evaporates, the strand shrinks back to where it started. What if human skin reacted the same way? Every time you stepped out of the shower, you would be taking a gallon of water with you! Imagine how your clothing would fit as your waist expanded and contracted by three or four inches!

Hair is a Hydrophile.

The term "hydrophilic" simply means "attracted to water", to be more specific, something that is hydrophilic is attracted to the hydrogen that is in water. The opposite is "hydrophobic" which means that something is repelled by water. Oil, for example, is hydrophobic. It is common knowledge that oil and water do not mix. Chemistry tells us that it's all about energy and how electrons attract or repel each other. For example, when wet hair comes into contact with a liquid that contains oil, the molecules undergo a change in energy that results in the oil leaving the water solution and attaching itself to the hair. This process is referred to as adsorption.

Adsorption is the transfer of a substance onto the surface of another whereas absorption is the transfer of a substance into another. With hair, both are possible because hair strands are primarily made up of keratin. Keratin consists of complex proteins that provide shape, strength and structure to the hair. It is also the very reason why hair can transform like nothing else on the human body. Keratin governs how permeable and adhesive the hair will be to anything that comes into contact with it and this is very important because without it, your hair would not be able to "hold" onto anything, including conditioners and moisturizers.

Is water a good moisturizer?

We know that humidity can wreak havoc on our hair if it's not properly moisturized. But isn't this a contradiction? If water is moisture then why is too much moisture bad?

Healthy hair contains a certain amount of water that has permeated into the shaft. The moisture content can rise or fall with the relative humidity but if the hair shaft is properly sealed, it stands a better chance of not drying out. If you feel that your hair is rough, dry, flyaway or frizzy, it is probably lacking moisture. But water alone is not going to save it. In fact, the temporary relief that water brings to dry hair can quickly make the situation worse. Remember the old saying "too much of a good thing"? When you over saturate dry, frizzy hair with water, the moisture will cause the strands to swell until the cuticles burst open. If you then let that water evaporate too quickly, your hair will be left more fragile and it will be prone to break. The key is to control the rate between moisture (water) gain and moisture loss. Too much and too quickly will do more damage than good.

To keep your hair properly moisturized, you need a balance between the absorption and adsorption of not just water but a combination of various proteins and other compounds that strengthen the hair. Aside from giving hair its structure, Keratin allows for biochemical bonds to take place. These bonds act as adhesives within the hair, giving it shape and texture. It is these bonds that are loosened when water, heat or styling products are applied to the hair and these bonds are what eventually break when you apply a chemical relaxer.

Moisturizers and Humectants

A true moisturizer is any ingredient that either helps your hair retain its natural moisture, proteins and oils (sebum) or supplies them from the outside in. Aloe Vera juice is an excellent example of a truly moisturizing ingredient. It evaporates at a much slower rate than water, which means it keeps the hair hydrated for extended periods of time.

Humectants are compounds that draw moisture from the atmosphere and pull it into the hairs' cortex. This happens gradually, over an extended period of time. Humectants work because the water is absorbed on a molecular level which means that the water molecules have time to bond with the hair. Vegetable glycerin is a good example of an organic compound that acts as a humectant.

Healthy hair thrives on moisture, so a good hair care regimen should include moisture rich products, including humectants to ensure constant hydration. Sealing the hair with a lightweight, non-synthetic oil will slow down moisture loss and provide a protective coating on the hairs surface. Properly and thoroughly moisturized hair resists breakage and splitting, so if your goal is to have long hair, be sure that you are giving it the moisture it craves.