Shedding light on alopecia: essential facts about hair growth, causes and types

  What is alopecia?  

Alopecia is a condition that is characterized by hair loss. It affects millions of people worldwide and can have different underlying causes. People with alopecia may experience localized patches of hair loss or complete loss of scalp or body hair. 

  How does hair grow?  

The hair growth cycle consists of three main phases:

  What causes alopecia?  

Hair loss occurs when the balance of hair growth and hair loss in the hair cycle is disrupted. 

• Hormonal imbalances play a significant role in hair loss, particularly in androgenic alopecia, where androgens like dihydrotestosterone (DHT) contribute to the miniaturization of hair follicles. 

• Autoimmune mechanisms, as seen in alopecia areata, are another critical factor, where immune cells erroneously target and attack hair follicles, leading to hair loss.¹ 

• Nutritional deficiencies, including insufficient levels of iron, zinc, or protein, can impair hair health and are commonly associated with conditions such as telogen effluvium. Stress, both physical and psychological, is a recognized trigger for temporary hair loss and can exacerbate pre-existing alopecia conditions. 

• Inflammatory and scarring processes, as observed in disorders like Lupus erythematosus or lichen planopilaris, result in chronic inflammation that irreversibly damages hair follicles.

• Genetic predisposition plays a pivotal role in hair loss, with a strong familial link evident in both androgenic alopecia and alopecia areata. 

  Types of alopecia  

Androgenic alopecia 

Also known as male or female pattern baldness, androgenic alopecia is the most common form of hair loss.³ It is progressive and typically follows a predictable pattern.

In men, androgenic alopecia starts at the temples and crown, progressing to baldness in severe cases. Women typically experience diffuse thinning over the crown without a receding hairline.

People with androgenic alopecia produce an excess of the hormone DHT, a derivative of testosterone, which causes very small and tight hair follicles. The hair growth cycle is out of balance, with shortened growth phases and prolonged resting phases, leading to thinner, shorter hair.

The severity of androgenic alopecia is classified with the Norwood Scale in stages from I to VII, with VII representing extensive hair loss across the crown and temples.⁴

Alopecia areata

Alopecia areata is an autoimmune condition where the own immune system attacks hair follicles, leading to hair loss in round or oval patches on the scalp or body.² It is non-scarring and often reversible. In severe cases, it can progress to alopecia totalis (complete scalp hair loss) or alopecia universalis (complete body hair loss).

The exact cause is unclear, but it involves genetic predisposition combined with environmental triggers such as stress or infections. The hair follicles prematurely enter the resting phase of the hair cycle and remain dormant without destruction.

T-cell-mediated autoimmune reactions play a central role in alopecia areata. Genetic susceptibility has been linked to the genes involved in immune regulation.

Telogen Effluvium

Telogen effluvium is a temporary hair loss condition triggered by a physiological or psychological stressor, causing more hairs than usual to enter the resting phase of the hair cycle simultaneously.⁵ Diffuse thinning is observed, typically without distinct bald patches.

Common triggers include surgery, childbirth, severe illness, or nutritional deficiencies. While largely non-genetic, susceptibility may be influenced by underlying predispositions.

Traction alopecia

This type of alopecia is primarily influenced by external factors, such as repeated mechanical stress or tension on hair follicles, for example certain hairstyles like tight braids or ponytails.⁶ Prolonged tension disrupts the follicle’s natural growth and may result in scarring and permanent loss in advanced stages. Hair loss occurs along the hairline or areas of sustained tension.

Scarring alopecia (Cicatricial alopecia)

This group of conditions involves irreversible destruction of hair follicles due to inflammation and scarring.⁷ It can be caused by autoimmune diseases (e.g., Lupus erythematosus), infections, or trauma. It is characterized by smooth, scarred patches with complete hair loss. Permanent damage to hair follicles eliminates their ability to produce new hair. The surrounding skin may exhibit redness or scaling.

  Conclusion  

There are different forms of alopecia with genetic and/or external causes. Androgenic alopecia is the most common form of alopecia and affects millions of men and women worldwide.

References

1. Rajabi F, Drake LA, Senna MM, Rezaei N. Alopecia areata: a review of disease pathogenesis. Br J Dermatol. Nov 2018;179(5):1033-1048. doi:10.1111/bjd.16808

2. Pratt CH, King LE, Messenger AG, Christiano AM, Sundberg JP. Alopecia areata. Nature Reviews Disease Primers. 2017/03/16 2017;3(1):17011. doi:10.1038/nrdp.2017.11

3. Lolli F, Pallotti F, Rossi A, Fortuna MC, Caro G, Lenzi A, Sansone A, Lombardo F. Androgenetic alopecia: a review. Endocrine. Jul 2017;57(1):9-17. doi:10.1007/s12020-017-1280-y

4. Norwood OT. Male pattern baldness: classification and incidence. South Med J. Nov 1975;68(11):1359-65. doi:10.1097/00007611-197511000-00009

5. Chien Yin GO, Siong-See JL, Wang ECE. Telogen Effluvium - a review of the science and current obstacles. J Dermatol Sci. Mar 2021;101(3):156-163. doi:10.1016/j.jdermsci.2021.01.007

6. Billero V, Miteva M. Traction alopecia: the root of the problem. Clin Cosmet Investig Dermatol. 2018;11:149-159. doi:10.2147/ccid.S137296

7. Cummins DM, Chaudhry IH, Harries M. Scarring Alopecias: Pathology and an Update on Digital Developments. Biomedicines. Nov 24 2021;9(12)doi:10.3390/biomedicines9121755