The fundamentals of androgenetic alopecia

by admin
February 28, 2017
Androgenetic alopecia, or male pattern baldness as it’s more commonly known, is a genetic condition that affects men and leads to the gradual thinning of hair with age. The cause of androgenetic alopecia is complicated. The condition is genetically inherited, stemming from both the mother and the father’s set of genes. The condition is passed down through the generations, it can also skip a few and resurface several generations later.

While the cause of androgenetic alopecia is harder to pinpoint, the process of androgenetic alopecia itself is fully understood. The actual process of thinning of the hair is an androgen-driven biological process called miniaturisation. Over time, miniaturisation decreases the calibre of the hair until the hair is no longer thick enough to block the light’s reflection on the scalp, which is when balding becomes noticeable.
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The different types of hair calibre

Hair follicles are divided into the three main types, to wit: terminal hairs, miniaturized hairs and vellus hairs. Terminal hairs have a calibre of about 60-84 micrometres and can be found on a healthy head of hair. Vellus hairs are fine, short hairs that are less than 30 micrometres in diameter and can be found in a number of areas on the body like the back of the ear. Miniaturized hairs are usually terminal hairs whose growth has been affected by hormones and they have a calibre ranging from 30 to 60 micrometres.

The appearance of a full head of hair is achieved by the presence of enough terminal hairs to block out the light’s reflection on the scalp. During hair transplant treatment, the follicles that are harvested from donor areas and transplanted onto recipient areas have to be terminal hairs in order to achieve the desired results. Hair follicles of a lesser calibre than 60 micrometres are not ideal.

The importance of hair calibre and hair mass index

As evidenced above, hair calibre is the critical factor when it comes to creating the appearance of a full head of hair. It also influences an important standard of measurement, the hair mass index (HMI). A patient’s hair mass index is used to determine, among other things, the extent of the patient’s hair loss, the type of alopecia that the patient has as well the progress of hair loss treatment once it has commenced. The hair mass index is determined through a method called cross-section trichometry (CST).

If you take a short segment of hair, what you essentially have is a cylinder, therefore you can easily determine the volume of the hair shaft by measuring the calibre (diameter) and height of the hair shaft and using them in the formula V=2πr²h. The hair mass index can thus be seen as aggregate of all of the volume of all the hairs on the patient’s scalp.

The greater the calibre of the hair, the bigger the volume of the hair shafts and the better the hair mass index. A good hair mass index means that more light bounces off the hair giving the appearance of fullness. Hair loss, therefore, isn’t due to hair falling out of the scalp but rather a gradual reduction in hair calibre (which is directly proportional to the volume of the hair shaft), eventually leading to hair that is too thin to reflect enough light to prevent the perception of baldness.

How does miniaturisation happen?

The hormone testosterone is converted into dihydrotestosterone (DHT), a type of androgen. Hair follicles have androgen receptors that DHT has an affinity to bind to. Patients with androgenetic alopecia have more of these receptors than individuals who do not have the condition. Once the DHT binds to these receptors, it alters the follicle’s ability to nourish the hair. The DHT interferes with the production of adenosine triphosphate (ATP) and the supply of oxygen. The result, over time, is miniaturisation of the hair with decreased calibre and length. If this continues for long enough, the hair becomes too thin to block the light from reflecting off the scalp and causing what we perceive as hair loss.

Book your appointment with Dr Nel today to find out what your hair mass index is and get a head start on your hair loss treatment.
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