The hair cycle is a three-phase process, one that takes place over a number of years. However, in this article I’m going to look more closely at the second phase, catagen.
First, I’ll outline the entire hair cycle, from anagen to catagen to telogen. This will provide you with the necessary background information. Then, I’ll discuss catagen hair loss (How common is it? What does it mean? Why does it happen?).
The Hair Growth Cycle
In mammals, the process of hair growth is not something that takes place all at once. Instead, it happens over a longer period of time (a few years, at most) and takes place in three different stages.
This is the stage of the hair growth cycle that’s most commonly referred to when people speak of the growth process. Actually, this is the only phase where active growth takes place.
Anagen phase growth begins when a telogen phase hair strand is pushed from the hair follicle and completely detaches. There is now room for new hair to grow, so in comes the anagen phase hair strand.
However, before that hair strand takes root, there are a few steps that must occur first.
- The hair follicle enlarges and deepens as it seeks to gain nutrients and blood supply from the dermal papilla (the structure at the very bottom of the hair follicle).
- Once the follicle has reached an appropriate depth, a hair bulb forms at the base of the follicle. This is where the new hair will grow from.
- With the bulb in place, the follicle is now able to fully attach to the dermal papilla. It’s at this point that full delivery of blood and nutrients is taking place.
- The hair strand grows upwards and, eventually outwards.
This stage of growth can last anywhere from two to six years.
Once the period of active growth has ceased, the transitional phase between anagen (active growth) and telogen (rest) takes place. This is known as catagen phase, and it can last from a few days to a few weeks.
The exact mechanism through which anagen phase ceases is unknown. However, it’s known that this signal alerts the hair bulb to detach from the blood supply (courtesy of the dermal papilla) and move upwards from the base.
Interestingly, the hair follicle shrinks in order to more easily push the shaft from the scalp. This results in the bulb becoming club-shaped, which is appropriately known as club hair.
At this point, the hair strand is held in place by the follicle. However, normal activity can easily dislodge the strand naturally.
The last stage of the hair cycle, the telogen phase of “growth” finishes up what catagen phase began. This is known as keratinization, and it’s the process in which hair changes from “terminal” to “club”.
The beginning of anagen phase and the ending of telogen phase tend to coincide, and for good reason. As the hair follicle widens during anagen phase to enable new hair to grow, this also allows the keratinized hair strand to fully shed.
In fact, shedding during telogen phase is so common that each person loses about 100 telogen phase hairs per day.
How can you tell it’s a telogen hair? Look at the strand.
It’s at this point in the hair cycle that the bulb and the hair shaft have fully fused. As such, if there’s a white bulb at the very bottom, this is a telogen phase hair.
Catagen Phase vs. Telogen Phase: What’s the Difference?
For many, the difference between the catagen and telogen phases of hair growth seem miniscule. However, there’s quite a bit that takes place between these two stages.
The main difference is that the process of keratinization begins in catagen phase but is complete in telogen phase. Once the hair has fully keratinized and become a club hair, catagen phase is complete and telogen has begun.
Hair Loss During Catagen Phase: Is It Normal?
There are two main categories of hair growth disorders. Those that occur during anagen phase, and those that occur during telogen phase. But, can hair loss take place during catagen?
The answer, of course, is yes.
Hair shedding can take place at any time during the hair cycle. And, while there are no particular conditions associated with catagen phase, you can still experience some catagen hair fall.
In the majority of cases, this is nothing to be worried about.
As catagen phase hairs are only loosely held by the hair follicle, it’s not uncommon for them to come out. So, when should you worry?
There are a few signs of early balding, including:
- Excessive shedding
- Noticeable thinning
- Reduced hair quality
- Slowed regrowth
- Hairline recession
Hair Loss and Catagen Phase: What’s the Link?
Unlike anagen phase and telogen phase, catagen phase doesn’t have any particular hair conditions associated with. So, what’s the link between catagen phase and hair loss?
Hair loss can have a number of causes. However, the majority of individuals with it suffer from a condition called Androgenetic Alopecia (AGA).
This is more commonly referred to as male-pattern baldness (or female-pattern baldness), and it affects over 80 million men and women in the United States alone.
While the exact mechanisms behind AGA aren’t known, it is known that DHT is a major trigger. This is a hormone – one that occurs naturally in both men and women – that is created through the interaction between testosterone and 5-alpha-reductase (an enzyme).
Unfortunately, some people are sensitive to this hormone, and this triggers irritation, hair miniaturization, and (eventually) baldness.
When miniaturization occurs, the hair follicle begins to spend less and less time in anagen phase. Instead, it transitions to catagen phase too quickly, and then enters telogen phase as a result.
In this way, catagen doesn’t play a direct role in hair loss, but it is part of the overall process.
Hair loss can happen at any stage in the hair cycle, though the two stages where shedding is most likely to occur is catagen (the transitional phase) and telogen (the resting phase).
This is because the hair is less firmly held in place by the follicle, and instead the hair is beginning to keratinize.
Remember to always talk to a qualified medical professional before you get started with any new hair loss treatment and go with FDA approved treatments when appropriate.