Rapunzel. Now there’s a case study in human hair and its growth cycles. Obviously, to have hair that long, the growth cycle on Rapunzel’s hair must have been rather lengthy.
Since we’re all about getting rid of unwanted hair at Romeo & Juliette Laser Hair Removal, here’s some background on how hair, wanted or unwanted, grows.
How It Grows
Human hair grows from deep within the hair follicles, which are thin cavities embedded in the dermis (the skin’s second layer). In most of these hair follicles you’ll also find sebaceous glands. The sebaceous glands produce oil that keeps the skin and the hair from drying out. Of course, if you’re a teenager, you’re cussing out the sebaceous glands, as their overproduction of oil is the root cause of acne.
Overall, humans have about 5 million hair follicles on our entire bodies, with men having a few hundred thousand more than women. The only places without hair follicles are our palms and the soles of the feet. Your hair color and ethnicity can dictate how many hairs you have on your scalp. Blondes have an average of 150,000 hairs. Redheads average around 90,000. Black- and brown-haired people have from 100,000 to 110,000 scalp follicles.
Hair doesn’t grow continuously but in a three-phase cycle. Your rate of hair growth varies by the individual and by the type of hair. For instance, the active growth phase for scalp hair may last several years (Rapunzel!), while the hair on the body has an active growth phase that may only last a few months.
Each growth cycle of each hair has three phases: anagen, catagen, and telogen. During the anagen phase, the hair grows actively from the follicle. It is anchored strongly into the follicle. The next phase, the catagen phase, is a short transitional period where the hair stops growing and the hair follicle begins to shrink. The follicle breaks away from the dermal papilla, which supplies nutrients to the hair follicle. Then the dermal papilla regresses downward. The last phase is the telogen, or resting, phase. In the telogen phase, the hair follicle grows back downward and reattaches to the dermal papilla. When this is complete, the hair follicle returns to the anagen/growth phase. As a new hair begins to grow, the old hair is pushed out and shed.
Lasers and Hair
This explains why multiple laser hair removal sessions are necessary. The hair must still be anchored in the follicle and its pigment must be at full color. This only happens in the anagen phase. During that phase, the hair’s pigment absorbs the laser energy, which travels down the hair shaft into the follicle. There, the heat damages the follicle, stopping hair growth. Because the hair isn’t connected to the follicle in the catagen or telogen phases, laser energy has no permanent affect on it.