Hair is approximately 91% protein. Cells form in the hair follicle and grow up and out, filling up with keratin on the way. By the time the hair is visible on the scalp, it is a dead strand of keratinized protein. It is no longer alive. Only the part of the hair beneath the scalp is actually living and growing.
On average, hair grows about 1/2 inch per month. The growth cycle of hair is usually four to five years. Then the hair follicle sheds the hair, rests, and starts the cycle over again. Most people shed around 100 hairs a day as this process occurs. Some hair will break off due to aggressive brushing, blow drying, flat ironing, etc. This is mechanical damage. Some hair will break off due to chemical damage from color applications, lightening/bleaching, permanent waving, relaxers, etc. These processes all force the cuticle of the hair open, causing weak points that will split and break. 
So, why does it seem that the hair is not growing for some people? Well - it IS growing. The problem is that when the hair is broken off, due to mechanical or chemical damage, it takes YEARS for that to come back.So, if you want to grow your hair longer there are several steps that must be followed.
1) Cut off damaged hair. Once hair ends split, it is like a "run" in ladies pantyhose: the split will travel up the hair shaft to the weakest point and break off. However, if you trim those split ends off (about a 1" trim every other month) before they break, you've only lost an inch of hair which will regrow in 8 weeks.Once the ends are healthy, you can reduce the trimming to a 1/4" every six weeks, leaving net length.
2) Hair needs moisture! Many, many products contain silicones or glycerines or other chemicals that work great the first few times you use them. Then a few weeks go by and you notice your hair is dryer than ever! This is because these products work by forcing the cuticle shut. A closed cuticle will appear smooth and reflect light, creating the shine we all crave. However, a cuticle that is glued shut cannot open to allow the natural exchange of moisture, therefore drying out the hair worse than ever. A good clarifying treatment is needed to remove the build up from these products.
3) Be Gentle. Wearing a tightly bound ponytail in the same place on the head over and over again will stress the hair being pinched into that tight elastic band (mechanical damage). If you wear a ponytail, try to not make it a tight one. Move the ponytail from the top of your head, to the back of your head, to the nape of the neck, or to one side or the other.
If you hear or feel ripping, crunching, or pulling when brushing your hair, you're causing mechanical damage! Use a wide-tooth comb or pick instead. It should slide quietly through the hair. If there is a knot, gently untangle it from the ends up to the roots using a wide tooth comb. Try not to rip through the hair.
Make sure all brushes and combs being used are clean. Stray hairs that collect on tools can weave their way into a nice tangle. http://www.hairfinder.com/tips/cleanbrushes.htm
Don't use hot water! Try to use the most tepid warm water when shampooing. Hot water forces the cuticle open. Cold water will shut it again and add shine. Always rinse hair with cold water (as cold as you can tolerate) after shampooing.
Wear a hat to protect your hair and scalp from the sun!
4) Be Kind. Any chemical service (color, perms, relaxer, etc) will cause some damage. In order to minimize damage, make sure your hair is as healthy as possible before doing the service. Take your stylist's advice on this as well. Any stylist worth their licensure will refuse to do any service that risks the integrity of the hair. Remember, you are walking around showing off that stylist's work, so if it looks awful it will affect their business.
5) Seek out Healthy Hair choices. Educate yourself. Ask your stylist WHY she prefers a particular product. Does it really improve your hair or is it just a commission based sale? Does the product do what it says it should do? Does the salon have a return or exchange policy?
6) When in Doubt...Seek the advice of a doctor, specifically a dermatologist or a trichologist, if you are fortunate enought to have one in your medical community. If your hair is still brittle, thinning, and delicate, consult a medical professional. These can be symptoms of many, many things, including endocrine disorders, thyroid malfunctions, and allergies. http://thyroid.about.com/cs/hairloss/a/hairloss.htm It's always better to find out it's nothing than to find out it was a fixable condition had you treated it sooner. My doctor has a sign in his office that says, "The worst words a doctor can hear from a patient: I thought it would go away."
I must conclude by saying that I am grateful to work for a haircare company that offers products that are all natural, with no silicones, glycerines, or harsh chemicals. Our products work by using the attraction between negative and positive particles, thereby actually pulling water molecules into the hair shaft, not coating the hair with anything artificial. I hope you request the e-Cure Treatment at your salon. It has helped restore my hair (which was severely damaged after perming over color).
I'm not writing this as a commercial, but as a testimonial. I love the products and I love hearing from salons all over the country on their successes with it. http://youtu.be/tIqgECdTHPM
source: Milady's Standard Cosmetology
