毛囊是小而複雜的結構，存在於哺乳動物，包括人類的皮膚中。它們負責生產毛髮並分佈於全身，除了手掌和腳掌等特定區域。毛囊包括多個層次，包括毛球、毛幹、內根鞘、外根鞘和真皮乳頭，每個層次在毛髮生長週期中扮演特定角色。
　　毛髮再生主要受到毛囊幹細胞控制。這些幹細胞位於稱為隆起的區域，位於豎毛肌和皮脂腺之間。毛囊幹細胞在毛髮生長週期中扮演關鍵角色，該週期包括三個階段：1.生長期：也就是活躍的生長階段；2.退化期：此時毛髮基質處會開始凋亡退化；3.休止期：此時毛髮再生會暫時休息。休止期結束後，毛髮脫落，週期以新的生長期重新開始。
　　毛囊幹細胞負責在這些週期中維持和再生毛髮。在生長期，毛囊中的幹細胞分裂和分化，產生新的毛髮細胞。當毛髮進入休止期時，幹細胞保持休眠，直到下一個生長期開始。
　　近年來，毛髮再生和幹細胞研究引起了極大的興趣，科學家們探索可能的治療方法來處理落髮和毛髮疾病。已進行了多項研究，探討刺激毛囊幹細胞或引入外源性幹細胞促進毛髮生長和再生的方法。然而，值得注意的是，儘管一些治療方法顯示出潛力，完全和持續的毛髮再生仍然是一個具有挑戰性的目標。
　　Hair follicles are small, complex structures found in the skin of mammals, including humans. They are responsible for producing hair and are distributed throughout the body, except for certain areas like the palms of the hands and soles of the feet. A hair follicle consists of several layers, including hair bulb, hair shaft, inner root sheath, outer root sheath and dermal papilla, each of which plays a specific role in the hair growth cycle:
　　Hair regeneration is mainly controlled by hair follicle stem cells. These stem cells are located in a region known as the bulge, which lies between the arrector pili muscle and the sebaceous gland. Hair follicle stem cells play a crucial role in the hair growth cycle, which consists of three phases: 1. Anagen Phase: The active growth phase; 2. Catagen Phase: A transitional phase; 3. Telogen Phase: The resting phase. After telogen phase, the hair sheds, and the cycle restarts with a new anagen phase.
　　Hair follicle stem cells are responsible for maintaining and regenerating hair throughout these cycles. During the anagen phase, stem cells in the hair follicle divide and differentiate to produce new hair cells. When the hair enters the telogen phase, the stem cells remain dormant until the next anagen phase begins.
　　Hair regeneration and stem cell research have gained significant interest in recent years, as scientists explore potential therapeutic approaches for hair loss and hair disorders. Several studies have been conducted to investigate ways to stimulate hair follicle stem cells or introduce exogenous stem cells to promote hair growth and regeneration. However, it is essential to note that while some treatments show promise, complete and consistent hair regeneration remains a challenging goal.