How Perms Work
From straight to curly, curly to straight, and everywhere in between, millions of people each year do something to change the texture and wave patterns of their hair. It's big business. There are many rules to remember, and some myths that need to be dispelled. So, let's talk about hair and perms.
Your hair is made up of proteins. Each strand has a cortex at the center. The cortex is made up of proteins in a chain down the length of the shaft. These proteins (called poly-peptide chains) are held together by peptide bonds which give the hair its strength.
The salt and hydrogen bonds are weaker than the disulfide bonds, but there are more of them, and overall, each of the bond types constitute about a third of the strength of the hair's curl. The disulfide bonds are what get changed in a permanent wave.
Finally, the cortex and medulla are encased in a protective sheath called the cuticle. The cuticle is made of tiny, overlapping scales of keratin (the same thing fingernails and toenails are made from). The cuticle is what protects the hair from damaging effects of the environment.
Some people have hair with a tightly closed cuticle, and some have a cuticle whose normal state is slightly raised. The arrangement of the hair's cuticle determines how readily the hair absorbs moisture, and how "frizzy" the hair appears to be.
Curling The Hair:
We change the wave pattern of the hair by curling it, usually on rollers of some type. These changes occur because we alter the side bonds of the hair. The salt and hydrogen bonds mentioned above are easily broken through the application of water and heat, which is why simply wetting the hair, wrapping it in rollers, and allowing it to dry - or using a curling iron - allows you to add curl.
When the heat cools and the hair dries, the salt and hydrogen bonds reform on their own. The curl you get this way only lasts until the next time the hair is wet. Hot combs and flat irons work on the same principles to relax curl and straighten the hair.
Perming The Hair:
The process we call permanent waving uses chemicals to break and reform the stronger disulfide bonds of the hair. When the hair is washed and wrapped on a perm rod (the rod size used determining the tightness of the curl), we place the hair in the physical shape we want it to take. Then, by applying a waving lotion with an alkaline base (ammonium thioglycolate is most commonly used in today's perms), we raise the cuticle layer and break the disulfide bonds that hold the natural wave pattern.
After the waving lotion has had time to process and has been rinsed away and the rods have been blotted to remove excess water, and a neutralizer is applied. The neutralizer is actually what reforms the disulfide bonds of the hair and sets the new curl pattern. It is also the most potentially damaging stage of the perming process and should always be closely monitored.
Once allowed to take effect, the neutralizer is rinsed away, the rods are removed, and the hair is re-rinsed for good measure, it can be styled as desired.