www.fda.gov/cdrh/consumer/laserfacts.html

It is important to note that the FDA DOES NOT approve or otherwise endorse lasers —or any type of hair removal equipment. The FDA issues clearance for intended use. All lasers must have safety clearance in order to be sold in the US and then some lasers have the additional clearance for permanent hair reduction.

Please note that clearance does not mean a certain laser is going to work for you. Studies conducted by the manufacturer and submitted to the FDA do prove that the laser worked for a majority of their test group but results vary from individual to individual and other factors (such as the practitioner) weigh heavily on the results.

Why one need to get multiple treatment? 

Histological features of the human hair follicle vary greatly during the growth cycle. All hair, terminal and vellus, goes through a growth phase (anagen), a regression or transitional phase (catagen), and a resting phase (telogen).

Laser hair removal is most effective while hair is at anagen stage:

Hair Structure and Hair Life Cycle

Hair Structure 

Hair is composed of strong structural protein called keratin. This is the same kind of protein that makes up the nails and the outer layer of skin.

Each strand of hair consists of three layers:

1. An innermost layer or medulla, which is only present in large thick hairs.
2. The middle layer known as the cortex. The cortex provides strength and both the color and the texture of hair.
3. The outermost layer is known as the cuticle. The cuticle is thin and colorless and serves as a protector of the cortex.

Structure of the hair root

Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is feed by the bloodstream, which carries nourishment to produce new hair. The dermal papilla is a structure very important to hair growth because it contains receptors for male hormones and androgens. Androgens regulate hair growth and in scalp hair Androgens may cause the hair follicle to get progressively smaller and the hairs to become finer in individuals who are genetically predisposed to this type of hair loss.

The Hair Growth Cycle 

Hair follicles grow in repeated cycles. One cycle can be broken down into three phases:

1. Anagen - Growth Phase
2. Catagen - Transitional phase
3. Telogen - Resting Phase 

 Each hair passes through the phases independent of the neighboring hairs.

Anagen Phase - Growth Phase

Approximately 85% of all hairs are in the growing phase at any one time. The Anagen phase or growth phase can vary from two to six years. Hair grows approximately 10cm per year and any individual hair is unlikely to grow more than one meter long.

Catagen Phase - transitional phase

At the end of the Anagen phase the hairs enters into a Catagen phase which lasts about one or two weeks, during the Catagen phase the hair follicle shrinks to about 1/6 of the normal length. The lower part is destroyed and the dermal papilla breaks away to rest below.

Telogen Phase - resting phase

The resting phase follows the catagen phase and normally lasts about 5-6 weeks. During this time the hair does not grow but stays attached to the follicle while the dermal papilla stays in a resting phase below. Approximately 10-15 percent of all hairs are in this phase at an one time.

At the end of the Telogen phase the hair follicle re-enters the Anagen phase. The dermal papilla and the base of the follicle join together again and a new hair begins to form. If the old hair has not already been shed the new hair pushes the old one out and the growth cycle starts all over again. 

Unwanted hair is carried out by transfer of laser energy to the hair follicle which absorbs the laser energy. This target is melanin, the pigment which is responsible for hair color. Melanin absorbs laser energy to a much more extent than other surrounding skin structures. When laser is fired energy is absorbed by hair melanin energy is converted into heat destroys the reproductive system of hair .

2. The Hair Follicle Structure

Hair follicle has germinative apparatus which is responsible for producing hair growth . Germinative apparatus is covered by melanin, it contains in the hair follicle. When laser is fired energy is transferred the to germinative apparatus and melanin causes very quickly increase in temperature. When there is enough laser energy is absorbed the high temperature rising can cause irreversible destruction to the hair germinative apparatus, resulting in permanent destruction of hair growth.

3. Melanin

Melanin ( color pigments) exists in the hair follicle and in the skin . Melanin amount changes person the person . Tanning is a extra melanin production by melanocytes, which produce melanin response to sun exposure or taning beds . The laser energy needs to go through the epidermis to reach the hair follicle, which resides within 2 to 5 millimeters deeper within the skin. Some Laser energy will be partially absorbed by epidermal melanin before it reaches the hair follicle. For a good treatment technician must exploit the differential absorption characteristics of melanin in the hair follicle vs. epidermal melanin, and also exploit the differential cooling characteristics of these two structures.

4. Cooling skin

The skin has a greater surface area compared to the cylindrical hair follicle, and will therefore cool faster. Hair follicle heat faster in response to laser energy, it will also cool slower. To further exploit this difference the skin surface can be cooled before, during, or after the laser fired by applying either a cooling spray (cryogen ) such as Candela corporation gentel lase, blowing cold air ( such as cynosure company ), cool and glide such as Cutera (altus corporation) or after treatment with ice packs . This will reduce the temperature of the skin surface, allowing more energy to be delivered to the hair follicle without producing damage to the overlying skin.

5.Treating high melanin skin (African Americans , dark skin types , Tanned skin) 

Lasers are well suited for the removal of unwanted hair, because with the right selection of parameters, they can be used as a non-invasive method to disable the hair structure without damaging the surrounding dermis and epidermis. Numerous hair follicles can be treated simultaneously allowing for rapid coverage of large areas.

Our CoolGlide Excel systems were the first Nd:YAG systems approved for use on all skin types and tanned skin, allowing treatment of a wider patient base than other systems. Independent control of pulse width and fluence allow effective treatment on a range of hair thicknesses, including the often difficult-to-treat finer hairs that are left by other systems after a number of treatments. As dark as skin type 6 African Americans can be easily and safely treated .

6.Treating low melanin skin such as skin types 2 , 3 (Caucations)  

We prefer to use Alexanderite laser by Candela corporation 755 nm wavelength cooling with crayogen . Over the years It has proven efficiency for permanent laser hair removal. It could easily treat skin type 2 to 4 fine hair to coarse hair very effectively .