Hair follicle

What is a hair follicle?

The hair follicle is the part of the skin where hair grows.

The health of the hair follicle is directly related to hair loss. Over the years, follicles age, shrink and produce finer hair.

Sometimes it may stop producing hair and close. This may occur on or before the age of one’s birthday, due to genetic causes, stress, etc.

Parts of the hair follicle

The hair follicle is formed by:

  • Sebaceous gland: they are located in the dermis and are responsible for the production of sebum, which is the hair’s lubricant.
  • Stem: this is the only part of the follicle that goes beyond the epidermis. It consists of pith, bark and cuticle.
  • Bulb: an extension of the hair follicle, which starts in the deepest part of the hair follicle. Cell division that gives rise to the hair takes place in the bulb.
  • Follicular canal: this is the area where the hair grows in the first instance.
  • Erector muscle: it is a small muscle composed of fibers and connected to the sympathetic nervous system. It is formed in the adjacent dermis and reaches the hair follicle in its middle part. It is directly involved in the reaction of the hair when an emotion occurs. This occurs when, within the hair follicle, the hair is tightened and bristles.
  • Follicular papilla: also known as dermal papilla. It is composed of fibroblastic cells that are responsible for the creation and cycling of hair.

Hair follicle cycle

The hair follicle growth cycle has three phases in which periods of growth alternate with periods of hair loss.

Anagen phase

The first phase of the hair cycle is the anagen phase, which is when hair grows. This phase does not have a defined duration, although it can last between 2 and 6 years, but it can be affected by external agents, such as stress situations, genetics or others.

Catagen phase

The catagen phase is when it stops its activity and no hair grows. This is a short phase, usually less than 30 days.

In this phase, the hair weakens, facilitating what will happen in the next phase.

Telogen phase

Finally, when the hair begins to fall out, it is called the telogen phase. At this stage the hair may fall out naturally or when touched. Although the hair falls out, the hair follicles remain in the skin to start a new process that repeats itself from the anagen phase.

Normally, most hair follicles are in the anagen phase. It should be noted that each follicle may have a different cycle. That is, not all hair grows, stops growing and falls out at the same time.

Commitment to quality

This text on the hair follicle has been written by professional editors and reviewed by Sisneo’s medical-aesthetic team. In addition, we have relied on experts in medicine, engineering and aesthetics as a source of information, as well as specific studies to maintain the quality of what we publish.

At Sisneo Bioscience we are committed to publish truthful and contrasted information. And to update or correct it as soon as new knowledge becomes available.

Among others, we have used the following references:

  • Ji, S., Zhu, Z., Sun, X. et al. «Functional hair follicle regeneration: an updated review» en Sig Transduct Target Ther 6, 66 (2021).
  • Stenn K, Parimoo S, Zheng Y, Barrows T, Boucher M, Washenik K. «Bioengineering the hair follicle» en Organogenesis. 2007 Jan;3(1):6-13. doi: 10.4161/org.3.1.3237.