Hair thinning, balding, and shedding are common hair-related disorders that are commonly seen in individuals as they grow older, however, these are more prevalent among men. Hair follicle miniaturisation is a hallmark of several hair loss conditions and may or may not be a reversible event.
Hair follicle miniaturisation reflects the changes in size and morphology of hair follicles as the hair strands become thinner until the state of having no hair strands at all, leading to diffuse hair loss and balding of the scalp.
The following sections of this article will educate the readers about the underlying mechanisms, common causes, signs and symptoms, and different treatment modalities for hair follicle miniaturisation.
What Is Hair Miniaturisation?
Figure 1. Simplified dermal mechanisms underlying terminal follicle cycling and miniaturisation
(Source: A bald statement-Current approaches to manipulate miniaturisation focus only on promoting hair growth, Pantelireis N. & Claire A. H., 2018)
Hair follicle miniaturisation is the hallmark of hair loss disorders including male and female pattern baldness, and alopecia areata. It is referred to the shrinking of hair follicles. Shrunken or constricted hair follicles do not facilitate healthy hair growth and lead to the formation of thinner hair and fragile hair shafts. These hair are susceptible to breakage and may also fall out relatively easily.
During the process of hair follicle miniaturisation, the hair follicles shrink as they progress from terminal to vellus-like hairs resulting in a reduced terminal to vellus hair ratio. This is a hormone-driven process that eventually leads to severe hair loss if not treated promptly and sufficiently. The process of hair follicle miniaturisation occurs as an abrupt step in one hair growth cycle, but it can keep progressing over several cycles.
Hair follicle miniaturisation occurs as the proliferation of hair follicular cells comes to a stop and the dermal papilla of hair follicles decreases in size and thickness. Hormonal and other factors disrupt the normal hair growth cycle leading to disruption of the proliferation of hair follicular cells resulting in hair follicle miniaturisation.
This is characterized by shorter anagen phases of the hair growth cycle and an increased latent lag period between anagen and telogen phases. Shortening of the anagen phase and prolongation of telogen-anagen transition is considered to be the primary mechanism of hair follicle miniaturisation.
Before learning about the causes and treatments of hair follicle miniaturisation, it's important to understand the normal human hair growth cycle.
What Is a Normal Human Hair Growth Cycle?
The normal hair growth cycle in humans is composed of the following phases.
Anagen or Growth Phase
During this phase, the hair follicles undergo rapid proliferation along with melanocytes that also produce melanin pigment. The rapidly dividing hair follicle cells cause the hair strands to grow longer and thicker as well as lead to increased deposition of the extracellular matrix.
The anagen or growth phase has a duration of approximately 2-6 years with about 80-95% of the total hair residing in this phase at any given time.
Catagen or Transitional Phase
Follicular regression is the hallmark of the catagen or transitional phase of the normal hair growth cycle. The average duration of the catagen phase in humans is 2-3 weeks. During this phase of the hair growth cycle, the hair follicles regress towards the surface of the scalp to facilitate the expulsion of the hair strand during the later stages.
During the transitional phase, the proliferation of melanocytes and hair follicular cells comes to a halt, and melanin production also declines. The root bulb, comprising keratin proteins, shrinks and forms a club-like structure at the hair roots. These are termed club hair.
Telogen or Resting Phase
During this phase, the hair follicles become dormant and hair strands are only loosely attached to the underlying hair follicles. On average, the telogen or resting phase lasts for about a year and involves approximately 10-15% of the total hair at a given time.
While the hair strands are shed during the exogen phase of the hair cycle, they may also fall off the scalp during the telogen phase during brushing or washing of hair. The exogen phase is a mere extension of the telogen phase characterized by the liberation of hair from follicles.
What Causes Hair Miniaturisation?
Following are some of the most important causes of hair follicle miniaturisation, thinning, and shedding of hair:
Some individuals are genetically susceptible to increased hair follicle miniaturisation and resultant thinning and shedding of hair. This is particularly evident in male pattern hair loss (MPHL) and female pattern hair loss (FPHL) as well as other hair loss conditions including alopecia areata.
In androgenetic alopecia, genetic alterations cause the androgen receptors on the hair follicles to become highly sensitive to circulating androgens, resulting in an exaggerated response of hair follicles to these hormones.
Hair follicle miniaturisation follows an X-linked inheritance pattern in the majority of the cases. Since males inherit only and females inherit two copies of the X chromosomes, men are more likely to suffer from hair loss disorders and hair follicle miniaturisation.
Both the hair growth cycle and morphology of the hair follicles are greatly influenced by the levels of different hormones in the body. In androgenetic alopecia, testosterone is actively converted to an androgen called dihydrotestosterone (DHT). This conversion is catalyzed by the enzyme 5-alpha reductase located within the hair follicles.
Increased levels of DHT suppress the proliferation of hair follicle cells as well as interfere with the hair growth cycle. This halts the growth of hair follicles and causes them to undergo hair follicle miniaturisation, further exacerbating hair loss via the growth of fragile and brittle hair strands.
Older adults tend to demonstrate increased miniaturised hair follicle as compared to other younger individuals. This is due to the fact that the prevalence and occurrence of pattern baldness increase with age, thus, miniaturisation is seen more frequently in these individuals.
Hair follicle miniaturisation may also be a manifestation of combined effects of age, genetic predilection, and increased sensitivity to DHT hormone.
Hair follicle miniaturisation is also observed in alopecia areata. Alopecia areata is referred to as an autoimmune condition that involves damage of hair follicles by the body's immune system. As compared to androgenetic alopecia which involves the gradual onset of hair follicle miniaturisation, alopecia areata is characterized by abrupt, yet, the reversible occurrence of miniaturisation.
Arector pili muscle plays a crucial in the onset of hair follicle miniaturisation and determines whether or not the condition is reversible upon adequate treatment. In male and female pattern baldness, only terminal hair is in contact with the arector pili muscle. Therefore, reversal of hair follicle miniaturisation in such cases is unpredictable and may be irreversible.
However, in individuals who are suffering from androgenetic alopecia, all of the miniaturised hair follicles maintain direct contact with the associated arector pili muscles. This is the major reason why hair follicle miniaturisation reverses upon prompt treatment of alopecia areata.
What Are the Symptoms of Hair Miniaturisation?
The signs and symptoms of hair follicle miniaturisation are coherent with the hair loss disorder an individual is suffering from. To determine whether you have hair miniaturisation, you need to know the signs of hair miniaturisation:
- Individuals suffering from hair follicle miniaturisation experience recession of hairline which can be defined as backward regression of the hairline across the scalp. Hairline recession may occur predominantly in the bitemporal regions of the scalp or may involve the frontal hairline as well.
- Hair thinning is also indicative of hair follicle miniaturisation. Males tend to experience hair thinning in the frontal, bitemporal, and crown regions of the scalp. However, in female patients, hair thinning usually involves lateral regions of the scalp while sparing the frontal scalp. Moreover, hair thinning tends to be diffused rather than localized in female patients.
- Individuals suffering from hair follicle miniaturisation tend to suffer from excessive hair loss. This is particularly evident during brushing and washing hair as well as people may notice heaps of hair strands on their clothes or pillow covers. Increased hair loss is attributed to brittle and fragile hair shafts that are inadequately supported by the shrunken or miniaturised hair follicles.
- Excessive hair loss may cause such individuals to undergo psychological distress or they may even tend to use harsh chemical products in the hopes of preserving hair volume. These actions may further exacerbate hair loss either due to direct damage of miniaturised hair follicles or through hormonal imbalances in stressful conditions.
- Hair follicle miniaturisation may also manifest as balding of the scalp. In individuals suffering from alopecia areata, small bald patches appear on the scalp. Other forms of hair loss may result in the widening of hair parting. Men, in particular, tend to suffer from scalp balding in the crown area with fringes of thinning hair in lateral and occipital regions of the scalp.
How to Diagnose Hair Miniaturisation?
For a proper treatment of hair follicle miniaturisation, it is important to diagnose the condition along with the underlying cause:
- The physician may order blood tests to determine hormonal imbalances and other pathologic markers of hair follicle miniaturisation.
- A hair pull test is also employed for the diagnosis of hair follicle miniaturisation. In this test, the physician or the patient himself/herself grabs a section of hair and gently pulls it upward. The pull test is usually performed at the vertex of the scalp. While falling off of two hair strands or less is considered normal, falling out of three or more hair strands indicates hair follicle miniaturisation.
- Hamilton-Norwood and Ludwig classification systems are used for classifying patterned hair loss in men and women respectively.
How to Treat Hair Miniaturisation?
Both natural and clinical modes of treatment are available to facilitate the reversal of hair follicle miniaturisation and promote the healthy growth of hair.
Natural treatments are a great alternative to pharmacologic formulations and have less severe side effects.
Pharmacologic formulations include minoxidil and finasteride, both of which are approved by the US Food and Drug Administration. Minoxidil promotes hair growth by causing vasodilation and promoting blood flow towards the hair follicles. It also stimulates the potassium channels and induces increased proliferation of the hair follicular cells.
Finasteride is an oral medication that is known for its activity against 5-alpha reductase. This drug is a competitive inhibitor of 5-alpha reductase, hence, suppressing the formation of DHT. This aids in the normal progression of the hair growth cycle.
Dietary and lifestyle modifications also play an important role in the treatment of hair follicle miniaturisation and hair loss conditions. Consumption of a healthy and well-balanced diet along with intake of required supplements correct the underlying nutritional deficiencies.
Eliminating environmental, social, and psychological stressors reduces the amounts of stress hormones and modulates other hormonal fluctuations to treat or minimize hair follicle miniaturisation.
Hair transplantation is also an effective treatment of hair thinning and associated hair follicle miniaturisation. The two commonly used hair transplant techniques include follicular unit extraction (FUE) and follicular unit transplantation (FUT).
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Hair follicular miniaturisation is indicative of thinning of hair and impaired proliferative activity of the hair follicular cells. Hair follicle miniaturisation occurs in pattern hair loss and alopecia areata. The proximity and attachment of miniaturised hair follicles with arector pilli muscles is the key factor for determining the progression of this condition.
The risk of hair follicle miniaturisation increases with genetic susceptibility, age, hormonal imbalances, and other health conditions. Individuals suffering from hair miniaturisation may present with the hairline recession, wider parting, bald areas on the scalp, and excessive shedding and thinning of scalp hair. This condition may be treated by using both herbal preparations and pharmacologic formulations.
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- Pantelireis, N, Higgins, CA. A bald statement — Current approaches to manipulate miniaturisation focus only on promoting hair growth. Exp Dermatol. 2018; 27: 959– 965. https://doi.org/10.1111/exd.13690