Except for certain circumstances, human hair is always either in the process of growing or falling.
Depending on which hair expert you consult, most humans lose between 75 and 150 hairs per day on a routine basis.
Hair growth cycles are controlled by a variety of factors which may include:
Hair on the head grows at a different rate than hair on the face, arms and legs or other parts of the body.
Scalp hair generally grows at the rate of 1/2 inch per month. There are exceptions to this rule depending on a wide range of factors.
Hair Growth Mechanics
So how does hair really grow? It's one of those amazing miracles of the human body.
The actual growth spot for hair is attached somewhere within the hair follicle near the intersection with the papilla, which is the base of the follicle.
As hair proceed through its natural aging cycle, it eventually loosens and slowly breaks away from the papilla.
The old hair is firmly held to the sheath that surrounds it and gradually moves upwards towards the surface of the skin.
When the aging hair is still a short distance from the papilla, a column of cells is automatically sent down towards the papilla. This group of newly released cells is the trigger of the spark that begins the generation of a new hair within the same follicle with the aging strand.
The new hair bulb, in its growth from the vital strand within the follicle, grows downward towards the papilla of the aging hair. Contrary to popular belief, the new replacement hair bulb grows down to the papilla, not up from it.
Eventually, once the new hair is firmly implanted into the papilla, it does begin to grow upwards towards the skin's surface. As the new hair grows upward, it gradually pushes the old hair out.
At some the original hair becomes loosened from the walls high up in the follicle and is dislodged completely in a number of ways. The hair can be brushed, combed or pulled out.
Or it may come out during the washing process, during sleep or just fall naturally. Some people have reported their old hair appears to just pop out.
New Hair Appearance
In some cases new hair may not appear immediately after the old hair has been shed.
A new hair will appear if the vital strand of cells was successfully deposited by the former hair. As long as the growth process continues its normal cycle, all is well and new hair will continue to appear.
In normal circumstances the rate of hair replacement keeps pace with the rate of hair loss. Problems do occur when the strands of hair growth cells are not deposited by old hair in order for new hair to be able to replace it.
It is very important to note that hair can only be formed by hair. Just like epidermic (skin) structures can only be produced by other epidermic structures.
Because the papilla in the hair follicle is not an epidermic structure, it cannot give rise to hair. The papilla's main role is to nourish the hair.
The influence of the papilla on regeneration of hair has been at times misrepresented by some experts.