What Causes Male Hair Loss
Male hair loss (androgenetic alopecia) is caused by dihydrotestosterone (DHT)-mediated miniaturization of genetically predisposed hair follicles on the scalp. 1, 2
Primary Pathophysiologic Mechanism
The fundamental cause involves two essential components working together:
- Genetic predisposition: Multiple genes must be inherited for androgenetic alopecia to develop, with the androgen receptor (AR) gene being the only one definitively identified to date 2
- Androgen-dependent process: Testosterone is converted to dihydrotestosterone (DHT), which drives the characteristic follicular changes 3, 4
DHT causes genetically susceptible hair follicles to progressively miniaturize, transforming from long growth (anagen) and short rest (telogen) cycles to short growth and long rest cycles until hairs become so fine they no longer emerge through the skin surface 2, 4
Clinical Pattern and Prevalence
The hair loss follows a highly reproducible pattern:
- Affected areas: Temples, vertex, mid-frontal scalp, frontal hairline, and crown 1
- Preserved areas: Temporal and occipital follicles remain intact 1
- Prevalence: Affects 58% of men by age 50 and up to 80% by age 80 1
The Hamilton-Norwood classification system standardizes the description of progression patterns 1
Distinguishing Features
On examination, the scalp appears normal without inflammatory scaling, which distinguishes it from seborrheic dermatitis 5. Dermoscopy reveals miniaturized hairs confirming the diagnosis 5, 1. The absence of exclamation mark hairs differentiates it from alopecia areata 1.
Genetic and Environmental Factors
- Family history is commonly present, indicating the major role of genetic factors 1
- Polygenetic inheritance pattern makes the condition susceptible to epigenetic and environmental influences 4
- The condition requires inheritance of several genes, though most remain unidentified 2
Key Clinical Pitfall
Do not confuse androgenetic alopecia with alopecia areata, which is an autoimmune T lymphocyte-mediated condition with completely different pathophysiology involving immune privilege failure in hair follicles 6. Alopecia areata presents with well-demarcated patches and exclamation mark hairs, whereas androgenetic alopecia shows gradual patterned thinning with miniaturized hairs 1, 6.