### Date : 2025-02-24 20:29 ### Topic : Androgenetic Alopecia (AGA) #dermatology #SMP #hairtransplantation #alopecia ---- # **Androgenetic Alopecia (AGA)** Androgenetic Alopecia (AGA) is the most **common cause of hair loss** in both men and women, often referred to as **male-pattern baldness (MPB) or female-pattern hair loss (FPHL)**. It is a **progressive, hereditary condition** driven by genetic and hormonal factors, primarily involving **androgens (male hormones), especially dihydrotestosterone (DHT)**. --- ## **1. What is Androgenetic Alopecia (AGA)?** ### **1.1 Definition** - **Androgenetic Alopecia (AGA)** is a **genetic and hormonally influenced** condition that leads to **gradual, patterned hair loss** on the scalp. - It is caused by the **miniaturization of hair follicles** due to the effects of **dihydrotestosterone (DHT)**. - AGA is **not a disease** but rather a **physiological response to genetic sensitivity to DHT**. ### **1.2 Epidemiology** - **Men**: 50% affected by age 50, 80% by age 70. - **Women**: 30% affected by age 50, with an increasing prevalence post-menopause. - More common in **Caucasians**, followed by Asians and Africans. - Can start as early as **late teens to early 20s** in genetically predisposed individuals. --- ## **2. Causes and Pathophysiology of Androgenetic Alopecia** ### **2.1 Genetic Factors** - AGA has a **strong genetic component**, inherited from **either the maternal or paternal side**. - **Polygenic inheritance**: Multiple genes contribute to AGA susceptibility. - **AR gene (Androgen Receptor gene)** on **chromosome X** plays a key role in AGA development. ### **2.2 Role of Androgens (DHT)** - **Testosterone** is converted into **Dihydrotestosterone (DHT)** by the enzyme **5α-reductase (Type II and Type I)**. - **DHT binds to androgen receptors** in scalp hair follicles, triggering: - **Follicular miniaturization**: Hair follicles shrink, leading to thinner, shorter hair. - **Shortened anagen (growth) phase**: Hairs grow for a shorter time before falling out. - **Increased telogen (resting) phase**: More hair enters the shedding phase. - **DHT-sensitive follicles are mainly located in the frontal, temporal, and vertex (crown) scalp**.  - **Occipital hair follicles** are resistant to DHT, which is why hair transplants use donor hair from this region. ### **2.3 Miniaturization of Hair Follicles** - Normal follicle cycle: **Anagen (growth) → Catagen (transition) → Telogen (resting/shedding) → Return to Anagen.** - In AGA: - The **anagen phase shortens** (normally lasts 2-6 years, but in AGA, it can be reduced to months). - The **telogen phase lengthens**, leading to increased **hair shedding**. - The **hair follicle becomes progressively smaller**, producing **vellus-like (thin, soft, colorless) hair**. - Eventually, the follicle becomes **dormant and stops producing hair**. --- ## **3. Clinical Features of Androgenetic Alopecia** ### **3.1 Male Pattern Hair Loss (MPHL)**  - Classified using the **Norwood-Hamilton Scale** (I-VII). - Begins with **bitemporal recession** → **thinning at the vertex (crown)** → progresses to complete baldness. - **Hairline recession** and **vertex thinning** are the hallmark signs. ### **3.2 Female Pattern Hair Loss (FPHL)**  - Classified using the **Ludwig Scale** (I-III). - **Diffuse thinning at the central scalp**, **widening of the midline part**. - Unlike men, **women usually retain their frontal hairline**. ### **3.3 Associated Features** - **Scalp remains normal** (no redness, inflammation, or scaling). - **Progression is slow** over several years to decades. - **No hair loss in the occipital area** (back of the head). --- ## **4. Diagnosis of Androgenetic Alopecia** ### **4.1 Clinical Diagnosis** - **History Taking**: - Onset, duration, family history of AGA. - Hair shedding pattern and presence of associated conditions (e.g., stress, hormonal imbalances). - **Physical Examination**: - Assess scalp hair thinning, miniaturization, and pattern of loss. - Look for signs of **[[female hyperandrogenism]]** (e.g., acne, hirsutism in PCOS). ### **4.2 Trichoscopy (Dermatoscope Examination)** - **Miniaturized hairs** (shorter, thinner, and variable in diameter). - **Increased hair follicle empty spaces**. - **Peripilar halo** (inflammatory pigmentation around follicles).  - **Variation in hair shaft diameter**. ### **4.3 Scalp Biopsy (If Needed)** - Shows **increased vellus hair percentage**. - **Perifollicular fibrosis** (chronic inflammation around hair follicles). ### **4.4 Laboratory Tests (If Female or Unusual Case)** - **Hormonal Tests** (to rule out underlying endocrine disorders): - **Testosterone, DHT, DHEA-S** (Androgens). - **TSH, Free T4** (Thyroid function). - **Ferritin** (Iron deficiency linked to hair loss). --- ## **5. Treatment Options for Androgenetic Alopecia** ### **5.1 Medical Treatments** #### **1️⃣ Finasteride (5α-Reductase Inhibitor)** - **Mechanism**: Blocks conversion of testosterone → DHT. - **Effect**: Slows hair loss and promotes regrowth. - **Dosage**: 1mg daily (oral). - **Side Effects**: Erectile dysfunction, decreased libido, gynecomastia. #### **2️⃣ Dutasteride (More Potent 5α-Reductase Inhibitor)** - Blocks **both Type I and Type II 5α-reductase** (more effective than Finasteride). - Used **off-label** for AGA. - **Side effects similar to Finasteride but stronger**. #### **3️⃣ Minoxidil (Topical Vasodilator)** - **Mechanism**: Prolongs anagen phase, increases blood supply. - **Dosage**: - 5% solution (men), 2% solution (women). - Applied **twice daily**. - **Side Effects**: Scalp irritation, increased shedding initially. #### **4️⃣ PRP (Platelet-Rich Plasma) Therapy** - **Mechanism**: Growth factors stimulate hair follicles. - **Efficacy**: Can be combined with Minoxidil/Finasteride. --- ### **5.2 Hair Transplant Surgery** - **FUT (Follicular Unit Transplantation)**: Strip harvesting from the occipital scalp. - **FUE (Follicular Unit Extraction)**: Individual follicle grafts extracted. - **DHT-resistant hair is transplanted** to balding areas. --- ### **5.3 Scalp Micropigmentation (SMP)** - **Ideal for** patients who: - Want the appearance of **a shaved scalp with uniform density**. - Have **insufficient donor hair** for a hair transplant. - Need to **camouflage transplant scars**. - **Non-invasive alternative** that creates **the illusion of hair follicles**. --- ## **6. Prognosis and Prevention** ### **6.1 Prognosis** - **Untreated AGA is progressive**. - **Early treatment is crucial** to preserving hair. ### **6.2 Prevention** - **Early use of Finasteride/Minoxidil**. - **Avoid smoking and poor diet**. - **Low-level laser therapy (LLLT)** may help stimulate follicles. --- ## **Conclusion** Androgenetic Alopecia is a **genetically and hormonally driven** condition that leads to **progressive hair follicle miniaturization**. 📌 **Early diagnosis and intervention** are key to slowing progression. 📌 **Medical treatments (Finasteride, Minoxidil) are first-line options**. 📌 **Hair transplants and SMP are effective for advanced cases**.