What is a Follicle?
A follicle is part of the body’s integumentary system, an organ system which prevents contaminants from entering the body. This organ system includes the skin, and the hairs by extension. In mammals, it is the structure which dots the scalp, among many other places along the body, and produces hair.
What is the Purpose of Hair?
Hair largely serves as a sensory device. The base of each and every hair has many sensitive nerve fibers which send signals whenever the exterior portion of the hair is stimulated through touch. Hair also protects the body from debris. Eyebrows and eyelashes catch debris before it can irritate the eye, and nostril hair keeps debris out by first ensnaring it, and then triggering a sneeze.
How Does A Hair Follicle Develop?
All hair has many different structures that enable it to grow hair. The most important ones are:
- The hair bulb – A complex structure located at the root of the hair. This where the hair first sprouts through cell division. The hair bulb eventually keratinizes once the hair is fully matured so that it can easily shed.
- The dermal papilla – This structure is made of connective tissue and is also at the base of the hair shaft. During the anagen (growth) phase, it connects into the hair bulb and supplies nutrition so that the hair may grow.
- The sebaceous gland – This gland secretes an oily lubrication that enables the hair to grow up the hair and emerge on top of the scalp.
What determines if I have Curly or Straight Hair?
The shape of the hair follicle determines the shape of the accompanying hair. A perfectly ovular hair follicle will produce straight hair. In contrast, a slightly less circular follicle will produce wavy hair, and a more narrow follicle is what produces hair that is curvy and kinky. There is no distinct advantage to having a particularly shaped hair follicles, though each hair type comes with its own unique characteristics.
Follicular Activity during the Three Stages of Hair Growth
The hair follicle plays an active role during the three stages of a hair’s lifecycle:
- Anagen – The hair follicle rapidly grows down into the scalp. When it reaches a certain depth, a hair bulb can form.
- Catagen – The hair follicle shrinks rapidly and cuts off blood supply to the hair shaft.
- Telogen – The hair follicle remains in rest for most of this stage. At the very end of the telogen phase, a new hair follicle will grow overtop the old one.
Hair Shaft and Miniaturization
The androgen known has DHT can reduce the ability to produce healthy new hair. Over time, DHT can have a shrinking effect on the diameter of the follicle itself. With a reduced diameter, it will produce thin, brittle hair that can shed easily. While this may impact the length of the anagen and telogen phases at first, eventually the follicular structure may be too narrow to develop hair at all. This process is known as miniaturization. Miniaturization can be addressed with medications such as Rogaine and Propecia.