Hair Facts

• There are close to 100,000 hairs on an average adult head.
• On a baby's head, there are about 2,800 follicles per square inch; by age 25 this number falls to 1,500, and to 635 by age 50.
• Each follicle grows about 20 new hair strands in a lifetime. Each strand grows for several years until it falls out.
• Most people lose between 100 to 150 hair strands per day.
• On average, your hair grows about ½ inch per month.

Hair Types: Straight, Wavy, Curly

Ever wondered why you were born with straight hair, curls or hair that's somewhere in between? Your hair type is all genetics, meaning that you inherited it from your parents, just like your eye color and skin tone.

Your hair type is determined by:

• The direction in which each strand of hair grows out of its follicle.
• The shape of the follicle itself, which determines the shape the strand of hair takes as it forms.

What do follicles look like for each hair type?

• Straight hair: The follicle is almost round and grows nearly perpendicular to the scalp.
• Wavy hair: The follicle is shaped like a kidney and grows at a slight angle to the scalp.
• Curly hair: The follicle has an elongated oval shape and grows at a sharp angle to the scalp.

Parts of the Hair

Your hair is made up of three layers:

The Outside Layer: the Cuticle

• Consists of flat, overlapping scale-like structures.
• Contains natural keratin protein and shields your hair's inside layers from damage.
• Determines the condition of your hair.

The Middle Layer: the Cortex

• Consists of spindle-shaped cells aligned along the fiber.
• Contains natural keratin protein and lies right under the cuticle.
• Accounts for 70%-90% of the your hair's bulk and provides remarkable strength.
• Houses your hair's color pigment.

The Core Layer: the Medulla

• Consists of a central core of diffuse, elongated cells.
• Exists only in some strands of hair.

Density

• Hair density is the amount of hair strands on the head. Generally, it
  is measured by counting the number of hair strands found in one square
  inch (2.5cm) of scalp. When a stylist tells you that you have thick hair,
  it is high density he/she is describing. Generally, the classifications of hair
  density are thin, medium, and thick, and are unrelated to the texture of
  the hair.

Texture

• Hair texture is the measure of the circumference of the hair strand
  itself. Professionals classify the texture of hair as being "coarse", "fine",
  or "medium". Coarse hair has the largest circumference, and fine hair has
  the smallest. Medium texture indicates a middle-range of the size of the
  hair shaft, it's considered normal and poses no special considerations
  regarding processing and chemical services. Coarse hair is stronger, for
  obvious reasons - it has more substance. However, coarse hair can also
  be harder to process, and can be resistant to haircoloring services,
  perming, and straightening. Fine hair, conversely, is often very easy to
  process, and can be over-processed easily and is susceptible to damage
  from chemical services.
          Hair texture varies from individual to individual, and can be different
  in separate areas of the same head. You may have coarse hair on the
  top of the head and fine hair at the nape of the neck. Race and ethnicity
  are irrelevant in determining hair texture, as coarse, medium and fine hair
  can be found among all racial and ethnic groups.
  

Porosity

• Porosity is the measure of the hair's ability to absorb moisture. This is determined
  by the condition of the hair's cuticle layer (the overlapping scales of the hair shaft), and
  is rated as low, normal, and high. In normal, healthy hair, the cuticle is compact and
  inhibits the penetration of the hair shaft by moisture - both moisture going in, and
  moisture coming out. When the cuticle is overly compact and prevents the penetration
  of the hair by moisture it has low porosity. Hair with low porosity is harder to process,
  and is resistant to haircolor and perms. Low porosity hair must usually be softened
  prior to other chemical services. Hair with high porosity is hair whose cuticle layer is
  open and the hair too-readily absorbs moisture. Overly-porous hair also releases
  moisture easily and becomes dry and is easily damaged. Acid-balanced conditioning
  treatments are used to contract the cuticle layer and lock-in moisture on overly-porous
  hair.

Elasticity

• The hair's elasticity is the measure of how much the hair will stretch
  (and return to a normal state). Healthy hair, when wet, will stretch up to
  50% of its original length and return to its normal shape without breaking,
  while dry hair will only stretch about 20%.
  Elasticity is rated as being low, normal, or high. Hair's elasticity comes
  from the side bonds in the hair shaft. Hair with normal and high elasticity
  is easily styled with wet-roller sets, thermal styling tools, etc., while hair
  with low elasticity may prove hard to curl, or lose its curl quickly.
          To test the elasticity of your hair, you need to select strands of
  hair from four different areas on the head. Be sure the hair is wet. Hold
  the strand securely and stretch the hair. If the hair stretches and returns
  to its original length when released, then it has good elasticity. If the hair
  breaks or doesn't return to its former shape, you have low elasticity.
          Hair with low elasticity is highly susceptible to breakage, will be hard
  to curl, and will not perm well.