Definition of the disease. Causes of baldness:
Androgenetic alopecia is hair loss as a result of hypersensitivity of hair follicles to androgens. In men, there is a bilateral lesion of the frontal-temporal areas with a lesion of the frontal hairline and a lesion of the crown. The code of androgenic alopecia in the International Classification of Diseases (ICD-10) is L64.
Androgenic alopecia is the most common type of baldness in men. It affects up to 50% of men under 50 years of age and 70% of older men. The disease is associated with increased sensitivity of fibroblasts (connective tissue cells) of hair follicles to oxidative stress.
Oxidative stress occurs with the increasing intake and/or formation of free radicals inside the body and cells and the predominance of oxidative reactions over reducing ones. Cells from the balding area are more sensitive to oxidative stress than cells from the occipital part not affected by baldness.
Androgenetic alopecia can begin at any age after puberty, but is usually most pronounced in 40-50 years.
The sensitivity to androgens inherent in each follicle and, consequently, the age of onset, the rate of development, the overall severity and type of hair loss are genetically predetermined. The type of inheritance is probably polygenic, i.e. dependent on several genes.
Symptoms of androgenic alopecia
- androgenetic alopecia in men usually begins with thinning of the hair in the frontal-temporal region and spreads to the crown (another option is also possible: thinning of the hair in the crown with a preserved frontal growth line, resembling a female type of baldness);
- the follicles of terminal hair transform and resemble the follicles of downy hair;
- long hair is replaced by thin light fluffy hair that is shorter and smaller in diameter.
Causes of baldness. Pathogenesis of androgenic alopecia
The mechanism of development of androgenetic alopecia:
Under the action of the enzyme 5-alpha-reductase contained in the cells of the hair bulb and the hair papilla, the sex hormone testosterone is converted into a more active androgenic hormone — 5-alpha-dihydrotestosterone (DHT).
DHT binds to the same cytoplasmic androgen receptor, but with greater strength, as a result of which it becomes biologically more active than its a precursor to testosterone.
An increase in the local concentration of DHT leads to a progressive reduction of anaphase (growth phase) due to the elongation of the telogen phase (loss or rest phase) and is accompanied by miniaturization of hair follicles.
The role of perifollicular inflammation: In addition to androgen-dependent changes, among the causes of androgenic alopecia are the effects of follicular microinflammation with the growth of connective tissue (fibrosis). Inflammation can be triggered by bacteria, toxins and oxidative stress.