### Date : 2025-02-17 23:37 ### Topic : ---- # **1.2 Hair Growth Cycle** Understanding the **hair growth cycle** is essential for **diagnosing hair loss, selecting transplant candidates, and ensuring graft survival** in hair transplantation. --- ## **1️⃣ Overview of the Hair Growth Cycle** The human scalp contains approximately **100,000–150,000 hair follicles**, each undergoing an **independent growth cycle** consisting of three main phases: |**Phase**|**Description**|**Duration (Scalp Hair)**|**% of Follicles in Phase**| |---|---|---|---| |**Anagen (Growth Phase)**|Active hair production|**2–7 years**|**85–90%**| |**Catagen (Transitional Phase)**|Follicle regression, detaches from blood supply|**2–3 weeks**|**1%**| |**Telogen (Resting Phase)**|Hair sheds, follicle remains dormant|**3–4 months**|**10–15%**| - **After telogen**, the follicle **re-enters anagen**, forming a **new hair strand**. - In **androgenetic alopecia (AGA)**, **DHT (dihydrotestosterone)** shortens the **anagen phase** and extends the **telogen phase**, leading to **thinner, miniaturized hair**. --- ## **2️⃣ Phase-Specific Details & Clinical Relevance** ### **1. Anagen (Growth Phase)** - Hair actively **grows from the follicle**. - **Dermal papilla supplies nutrients & growth signals**. - Determines **final hair length** (longer anagen = longer hair). 💡 **Clinical Relevance:** ✅ Ideal phase for **hair transplantation** → follicles are in **active growth**. ✅ Prolonged anagen phase = **better donor area density**. ❌ In **AGA**, the anagen phase progressively **shortens** → hair thins over time. ✅ Treatments like **Minoxidil** prolong the anagen phase. --- ### **2. Catagen (Regression Phase)** - Short-lived **transition phase**. - The **hair detaches from dermal papilla** (stops growing). - Follicle **shrinks** but remains under the skin. 💡 **Clinical Relevance:** ❌ **Transplanting catagen-phase follicles** results in poor growth. ✅ Rarely a concern, since **only ~1% of hairs** are in catagen at a time. --- ### **3. Telogen (Resting & Shedding Phase)** - **Follicle remains inactive**, preparing for the next cycle. - Old hair **sheds** and a new hair begins growing **underneath**. - Normal daily shedding: **50–100 hairs**. 💡 **Clinical Relevance:** ❌ **Telogen Effluvium (TE)**: **Stress, illness, or surgery** can push follicles into telogen prematurely → **increased shedding**. ❌ **Shock Loss After Transplant**: Some native hairs enter telogen due to surgical trauma but **regrow within 3–6 months**. ✅ **PRP therapy** can shorten telogen and **restart anagen faster**. --- ## **3️⃣ Hair Cycle Disruptions in Hair Loss Disorders** |**Condition**|**Effect on Growth Cycle**| |---|---| |**Androgenetic Alopecia (AGA)**|Anagen shortens, Telogen prolongs, Follicles miniaturize| |**Telogen Effluvium (TE)**|Sudden shift from anagen to telogen → rapid shedding| |**Alopecia Areata**|Autoimmune attack stops follicles from entering anagen| |**Scarring Alopecia**|Follicles permanently destroyed (no new growth)| 💡 **Clinical Implication:** - In **AGA**, transplanted hair **retains its original anagen duration** from the donor area. - **Telogen Effluvium is reversible**, but **scarring alopecia is not**. --- ## **4️⃣ Optimizing Transplant Outcomes Based on Hair Cycle** ### **Preoperative Phase** ✔ **Assess anagen percentage** in the donor area using **trichoscopy**. ✔ **Pre-treat with Finasteride/Minoxidil** (stabilizes miniaturization, prolongs anagen). ✔ **Avoid transplanting telogen hairs** (higher risk of shedding). ### **Postoperative Phase** ✔ **PRP & Low-Level Laser Therapy (LLLT)** → Stimulate anagen regrowth. ✔ **Educate patients on shock loss (temporary telogen phase transition after surgery).** ✔ **Monitor hair regrowth over 12 months**, as follicles re-enter anagen at different times. --- ## **📌 Key Takeaways** ✅ **Anagen phase** is the ideal transplant phase for graft survival. ✅ **Minoxidil & Finasteride prolong anagen and reduce telogen phase.** ✅ **Shock loss occurs when transplanted & native hairs enter telogen after surgery.** ✅ **Hair cycle disorders like AGA and Telogen Effluvium affect transplant outcomes.** --- # **1.2.1 How to Differentiate Anagen vs. Telogen Hair with the Naked Eye** Differentiating **anagen (growth phase) hairs** from **telogen (resting/shedding phase) hairs** is **crucial** in hair transplantation, trichology, and diagnosing hair disorders like **telogen effluvium and androgenetic alopecia**. --- ## **1️⃣ Key Differences Between Anagen and Telogen Hair** |**Feature**|**Anagen Hair (Growing Hair)**|**Telogen Hair (Shedding Hair)**| |---|---|---| |**Length**|Long (actively growing)|Shorter (no growth)| |**Root Shape**|**Tapered, rounded root with sheath**|**Club-shaped bulb (white tip)**| |**Color**|Dark (contains melanin)|White or translucent (keratinized bulb)| |**Texture**|Thick, strong|Thin, fragile| |**Attachment**|Firmly attached to the scalp|Loosely attached, easily shed| --- ## **2️⃣ How to Identify Hair Phases with Naked Eye** ### **A. Root Examination (Most Reliable Method)** 1. **Gently pluck a hair** from the scalp using tweezers. 2. Observe the **root end** under good lighting. 🔹 **Anagen Hair (Growing Phase)** - Root is **tapered, elongated, and dark-colored**. - Often surrounded by **root sheath material** (visible debris around the root). - Difficult to remove manually—**strong attachment to the scalp**. - Found mainly in **healthy donor areas**. 🔸 **Telogen Hair (Shedding Phase)** - Root is **club-shaped, white/translucent**, and lacks a sheath. - Falls out easily **without pain or resistance**. - Found in patients with **telogen effluvium or post-transplant shock loss**. --- ### **B. Hair Pull Test (Quick In-Clinic Test)** **Purpose**: To assess excessive shedding and detect telogen effluvium. **How to Perform:** 1. Grasp **~50–60 hairs** between thumb and forefinger. 2. Gently pull while applying slight traction. 3. Count the number of extracted hairs. ✅ **Normal Shedding:** **0–2 telogen hairs**. ❌ **Telogen Effluvium (>10% shedding):** **5–10+ telogen hairs** → Suggests **acute hair loss**. --- ### **C. Washing and Comb Test** **Purpose**: Evaluate **shedding patterns**. - **Anagen Hair Loss:** Few hairs lost per day, **mostly tapered roots**. - **Telogen Hair Loss:** **Excessive hair loss** in the shower or when combing. Shed hairs **have club-shaped roots**. 💡 **Key Insight:** Patients with **telogen effluvium or post-transplant shock loss** will report seeing **many club-shaped white hairs on their pillow, comb, or shower drain**. --- ## **3️⃣ Clinical Relevance in Hair Transplantation** 1️⃣ **Donor Site Selection:** - Ideal donor area has **90%+ anagen hairs**. - Avoid extracting telogen hairs (they will **shed and not regrow** after transplantation). 2️⃣ **Postoperative Shedding (Shock Loss):** - Normal post-FUE/FUT shedding occurs in **1-3 months** due to a shift from anagen → telogen. - **Telogen hairs in the recipient area will regrow after re-entering anagen (~4–6 months post-op).** 3️⃣ **Hair Loss Diagnosis:** - **AGA (Male/Female Pattern Baldness):** Miniaturization, shortened anagen phase. - **Telogen Effluvium:** High proportion of club hairs in shedding. --- ## **📌 Key Takeaways** ✅ **Anagen hairs** = Tapered root, firmly attached, dark, long. ✅ **Telogen hairs** = Club-shaped white bulb, shed easily, shorter. ✅ **Hair Pull Test** helps assess excessive telogen hair shedding. ✅ **Post-transplant shock loss** mainly affects telogen hairs, which regrow later. --- ### **Next Steps** Would you like to: 1️⃣ Study **1.3 Hair Follicle Anatomy** next? 2️⃣ Analyze **real case images of anagen vs. telogen hairs**? 3️⃣ Learn how to prevent **shock loss after hair transplant**? Let me know how you'd like to proceed! 🚀