A Review of Hair Anatomy and Animal Models for Alopecia

Hair is part of the integumentary system and it sits in the hair follicle, which extends into the skin. Hair serves several functions, including protecting the skin and regulating body temperature. Understanding the hair growth cycle is crucial as it is a complex process that involves four distinct phases: Anagen, Catagen, Telogen, and Exogen. These phases are regulated by various factors, such as hormones and genetics. An imbalance in the hair growth cycle can lead to hair loss or Alopecia, Various etiological factors cause hair loss; these include genetic factors, hormonal imbalances, medication, poor diet intake, smoking and environmental factors. In general, alopecia classified into Alopecia areata, Androgenic alopecia, Alopecia universalis, Involutional alopecia, Telogen effluvium, Trichotillomania, and Scarring alopecia. Several animal models have been utilized to study the pathophysiology of Alopecia. These models include mice, and rats similar to human hair and physiology used to study the pathway of Alopecia. Based on the type of Alopecia, animal models differ as androgenic Alopecia occurs due to testosterone sensitivity or due to the Dihydrotestosterone (DHT) hormone, chemotherapy-induced alopecia and alopecia areata by using transgenic animals and C3H/HeJ mice models. The present review provides insight into the anatomy and physiology of the hair and utilizes animal models which can aid in developing new treatment approaches for Alopecia.