Chapter 6 - Section 6.2 - Study Guide - Assess Your Learning Outcomes - Page 199: 7

The hair growth cycle consists of three main stages: anagen, catagen, and telogen. These stages are part of the natural process of hair growth and shedding, and they occur in a cyclic manner. Here are the events of each stage, along with the typical lifespan and growth rate of scalp hairs: **1. Anagen Stage (Growth Phase):** - **Duration:** The anagen stage is the active growth phase of a hair follicle. - **Duration on the Scalp:** This phase can last for several years on the scalp, with the exact duration determined by genetics. - **Events:** - During anagen, the hair follicle is actively producing new hair cells. - The hair shaft grows longer during this phase, and it can continue to lengthen as long as the anagen stage persists. - Approximately 85-90% of the hairs on the scalp are in the anagen stage at any given time. - The hair matrix at the base of the hair bulb actively divides, producing the hair shaft. - Hair cells are filled with keratin, and the hair becomes stronger and thicker. **2. Catagen Stage (Transitional Phase):** - **Duration:** The catagen stage is a transitional phase between growth and rest. - **Duration on the Scalp:** This stage lasts for a few weeks. - **Events:** - During catagen, the hair follicle begins to shrink and detach from the dermal papilla, which is responsible for nourishing the hair. - Hair growth stops during this phase. - Approximately 1-2% of the hairs on the scalp are in the catagen stage at any given time. - The hair follicle is preparing to enter the telogen phase. **3. Telogen Stage (Resting Phase):** - **Duration:** The telogen stage is a resting phase where the hair is no longer actively growing. - **Duration on the Scalp:** This stage can last for a few months. - **Events:** - In telogen, the hair follicle remains dormant and detached from the dermal papilla. - The hair is fully formed but not actively lengthening. - Approximately 10-15% of the hairs on the scalp are in the telogen stage at any given time. - Eventually, the old hair shaft is pushed out by the growth of a new anagen hair from beneath it. - This phase precedes the shedding of the old hair. **Typical Lifespan and Growth Rate of Scalp Hairs:** - **Lifespan:** The average lifespan of a scalp hair is about 2-7 years. This lifespan is largely genetically determined, which is why some people can grow their hair longer than others. - **Growth Rate:** The average hair growth rate is approximately 0.3 to 0.5 millimeters per day, or about half an inch per month. However, individual variations in growth rate exist, and factors like age, genetics, and health can influence the speed of hair growth. It's important to note that not all hairs on the scalp are in the same stage of the hair growth cycle at the same time. This is why we don't lose all of our hair at once but continually shed and replace hairs as they go through the various stages of the cycle. The proportion of hairs in each stage at any given time can vary among individuals.

The hair growth cycle consists of three main stages: anagen, catagen, and telogen. These stages are part of the natural process of hair growth and shedding, and they occur in a cyclic manner. Here are the events of each stage, along with the typical lifespan and growth rate of scalp hairs: **1. Anagen Stage (Growth Phase):** - **Duration:** The anagen stage is the active growth phase of a hair follicle. - **Duration on the Scalp:** This phase can last for several years on the scalp, with the exact duration determined by genetics. - **Events:** - During anagen, the hair follicle is actively producing new hair cells. - The hair shaft grows longer during this phase, and it can continue to lengthen as long as the anagen stage persists. - Approximately 85-90% of the hairs on the scalp are in the anagen stage at any given time. - The hair matrix at the base of the hair bulb actively divides, producing the hair shaft. - Hair cells are filled with keratin, and the hair becomes stronger and thicker. **2. Catagen Stage (Transitional Phase):** - **Duration:** The catagen stage is a transitional phase between growth and rest. - **Duration on the Scalp:** This stage lasts for a few weeks. - **Events:** - During catagen, the hair follicle begins to shrink and detach from the dermal papilla, which is responsible for nourishing the hair. - Hair growth stops during this phase. - Approximately 1-2% of the hairs on the scalp are in the catagen stage at any given time. - The hair follicle is preparing to enter the telogen phase. **3. Telogen Stage (Resting Phase):** - **Duration:** The telogen stage is a resting phase where the hair is no longer actively growing. - **Duration on the Scalp:** This stage can last for a few months. - **Events:** - In telogen, the hair follicle remains dormant and detached from the dermal papilla. - The hair is fully formed but not actively lengthening. - Approximately 10-15% of the hairs on the scalp are in the telogen stage at any given time. - Eventually, the old hair shaft is pushed out by the growth of a new anagen hair from beneath it. - This phase precedes the shedding of the old hair. **Typical Lifespan and Growth Rate of Scalp Hairs:** - **Lifespan:** The average lifespan of a scalp hair is about 2-7 years. This lifespan is largely genetically determined, which is why some people can grow their hair longer than others. - **Growth Rate:** The average hair growth rate is approximately 0.3 to 0.5 millimeters per day, or about half an inch per month. However, individual variations in growth rate exist, and factors like age, genetics, and health can influence the speed of hair growth. It's important to note that not all hairs on the scalp are in the same stage of the hair growth cycle at the same time. This is why we don't lose all of our hair at once but continually shed and replace hairs as they go through the various stages of the cycle. The proportion of hairs in each stage at any given time can vary among individuals.