The Life Cycle of Hair

Did you know the average person loses 50-100 strands of hair daily? This is also called natural hair fall during the life cycle of hair. The three stages of hair growth are easy to remember if you had to take the ACT in high-school! "A" is Anagen, "C" is for Catgen and "T" is for Telogen! Now let's break it down!

This is when hair actively grows. Its duration varies among individuals, typically lasting between 2 to 7 years. The length of this phase determines how long hair can grow. For instance, scalp hair follicles can remain in the anagen phase for 2 to 8 years, allowing for significant length in some individuals.
source: healthline.com

A brief period lasting about 2 weeks where hair growth stops, and the follicle shrinks.

Lasting around 3 months, this phase involves the shedding of hair and the resting of the follicle before a new hair begins to grow.

After a severe bodily trauma or stress, sometimes MANY more strands than usual are zapped into Telogen. When people talk about "all their hair falling out", it is typically 3 months after the event.

Same applies to postpartum hair loss in women. Many strands hold onto Anagen phase during pregnancy due to hormones, nutrients etc. Birthing a baby also will "zap" some strands into telogen as well. So the usual daily hair fall of 50-100 strands builds up over 9 MONTHS in conjunction with the "zapped" strands. Hair appears to be SUPER thin and that is because of these factors. Usually within 12 months postpartum, hair stabilizes and returns to normal. There is texture change sometimes, and than can be due to the "restart" follicles of Anagen changing SHAPE due to the hormonal shift in the body. I will go into follicular shape soon!  

On average, scalp hair grows approximately 0.5 inches (1.25 cm) per month, equating to about 6 inches (15 cm) per year. 

philipkingsley.com

• 2-Year Anagen Phase: 6 inches/year × 2 years = 12 inches (30 cm)
• 7-Year Anagen Phase: 6 inches/year × 7 years = 42 inches (107 cm)

Therefore, an individual with a 2-year anagen phase would achieve a maximum hair length of approximately 12 inches, which often reaches around shoulder length. Conversely, someone with a 7-year anagen phase could grow their hair up to 42 inches, potentially reaching waist length or longer.

Genetics play a crucial role in determining the duration of the anagen phase. Conditions like Short Anagen Syndrome are characterized by a shortened growth phase, leading to an inability to grow hair beyond a certain length. In this syndrome, the hair shaft is otherwise normal, apart from its length. 

dermnetnz.org

The length of the anagen phase is a key determinant of how long hair can grow. A genetically shorter anagen phase results in shorter maximum hair length, as hair follicles transition more quickly through the growth cycle. Therefore, if someone's DNA causes all their hair strands to enter the shedding phase after 2 years, their hair would likely not grow much past shoulder length.