Understanding hair science

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If you are a young man you have probably never given your hair much thought.  But as we age, hair tends to dominate our thoughts.  In fact, as it starts to thin and fall out, we find ourselves quite desperate to maintain our luscious locks of youth.

To fully understand hair loss, we must first study the science of hair.  From the structure to the growth cycle, hair is actually quite complex.

From the beginning

Just after the halfway point of a women’s pregnancy (22 weeks), her developing fetus has already formed all of its hair follicles.  And the amount of hair follicles that tiny human being has amassed is staggering – five million!  More surprisingly, only about one hundred thousand of those follicles are on the scalp.  The rest are distributed throughout the body – arms, legs, eyebrows, eyelashes, etc.

Since humans do not obtain new hair follicles throughout their life, the amount a person is born with is the most they will ever have.  Most people notice a decrease in density as they pass from childhood to adulthood.  This isn’t just an illusion; our scalps stretch as we age and our follicles move farther apart.

Hair has two distinct structures.  The hair follicle resides in the skin.  The shaft is visible above the scalp.

The hair follicle

The hair follicle is a tunnel-like organ that passes through the epidermis to the dermis layer of skin.  The base of the follicle is filled with capillaries (tiny blood vessels) which nourish the hair cells.  Cells in the hair follicle divide significantly faster than any other cell in the body (every 23 to 72 hours).

Connected to the hair follicles are sebaceous glands.  These microscopic glands secrete an oily/waxy substance called sebum.  Sebum is vital to hair health because it lubricates, conditions, and waterproofs the skin and hair.  After puberty, sebum production spikes but then starts to decline as we age.  Also, as our years progress, women produce much less sebum than men.  Hair density also affects the amount of sebum; the thicker the hair, the more sebaceous gland present.

The hair shaft

The hair shaft consists of three layers – the medulla, cortex, and cuticle.  All three layers are made of a hard protein called keratin.

The majority of the hair shaft is the cortex (middle) layer.  The cuticle (outer) layer consists of shingle-like, overlapping scales.  A hair’s color is determined by the pigment stored in both the cortex and medulla (inner) layers.

The growth cycle of hair

Unlike other mammals, the hair growth cycle for humans is not seasonal.  Our hair grows and sheds randomly.  Also, there are three stages of hair growth: anagen, catagen, and telogen.  At any moment, a random number of hairs will be in one of these three stages with all three stages being present at once.  These length of time a hair remains in each phase can be affected by hair color and follicle shape.

The Anagen Phase

The anagen phase of hair growth is the active phase.  During this phase, cells in root of the hair are working hard, dividing at an extremely rapid rate.  As the new hair grows, it pushes out the club hair (a hair that previously sprouted out of the same follicle but has stopped growing).

The amount of time a hair spends in the anagen phase determines how long the hair is.  Some people have difficulty growing their hair long; it seems to stop growing at a certain length.  These people have a short active phase of growth.  On the other hand, some people have very long hair because their anagen phase is much lengthier.  Usually, scalp hair will remain in the anagen phase for two to six years and grow about 1cm every 28 days.  Hair on other parts of the body – eyelashes, eyebrows, arms, legs – have a very short anagen phase.  These hairs are only active for about 30 to 45 days, explaining why they are so much shorter than scalp hair.

The Catagen Phase

About three percent of all scalp hairs are in the catagen (transitional) phase at any given moment.  Club hairs begin to form during this phase.  Typically, the catagen phase lasts about two to three weeks.

The Telogen Phase

The telogen phase is the resting phase.  About six to eight percent of all hairs are in the telogen phase.  By this point in the growth cycle, the club hair is fully formed and growth is at a complete standstill.  For hairs on the scalp, this phase will last about 100 days.  Hairs on the eyebrows, eyelashes, arms and legs will be in the telogen phase much longer.

Hair loss

When a hair reaches the end of the growth cycle, it falls out.  It is totally normal for about 25 to 100 telogen hairs to shed each day.  When more than 100 hairs are lost, clinical hair loss may occur (referred to as telogen effluvium).  Another type of hair loss is called anagen effluvium and happens when there is a disruption of hair growth during the anagen phase.

Understanding the different causes of hair loss is important when determining the correct hair restoration process.  meeting with a restoration specialist for is important when deciding on a hair loss treatment plan.

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