The catagen phase is the shortest stage of the hair growth cycle, lasting only about 2 to 3 weeks. For comparison, the growth phase (anagen) runs 2 to 6 years on scalp hair, and the resting phase (telogen) lasts 3 to 6 months. Catagen is a brief but critical transition period where the hair follicle shuts down active growth and prepares to release the strand.
The Four Stages of Hair Growth
Every hair on your body cycles through four distinct phases, each with a different job and timeline. Understanding all four puts catagen’s brevity into perspective.
Anagen (growth phase): This is when the follicle actively produces new hair cells, pushing the strand longer. On your scalp, anagen lasts 2 to 6 years, which is why head hair can grow so long. For eyebrows, it lasts only 4 to 8 weeks, and for eyelashes, roughly 1 to 2 months. The length of anagen is the single biggest factor determining how long any given hair can get.
Catagen (transition phase): At just 2 to 3 weeks, this is the shortest stage regardless of where the hair grows. Interestingly, catagen takes about the same amount of time for scalp hair, eyelashes, and eyebrows. While anagen and telogen vary dramatically by body location, catagen stays remarkably consistent.
Telogen (resting phase): The follicle sits dormant for 3 to 6 months on the scalp, or 2 to 3 months for eyebrows and eyelashes. The old hair strand stays anchored in place but is no longer growing.
Exogen (shedding phase): The old hair finally releases from the follicle and falls out, often as a new anagen hair is already forming beneath it. This is the shedding you notice in your brush or shower drain.
What Happens During Catagen
Catagen is essentially a controlled shutdown. The follicle stops producing new cells, and the lower portion of the follicle shrinks and detaches from its blood supply. Without that blood flow, the hair strand can no longer receive the nutrients it needs to grow. The strand becomes what’s called a “club hair,” anchored loosely in the follicle but disconnected from the growth machinery below.
During these 2 to 3 weeks, cells in the lower follicle undergo programmed cell death. The follicle can shrink to roughly one-sixth of its original length. This isn’t damage. It’s a tightly regulated process that allows the follicle to reset before entering the resting phase and eventually producing a brand-new hair.
How Many Hairs Are in Catagen Right Now
Because catagen is so short, very few of your hairs are in this stage at any given moment. The traditional estimate holds that 85% to 90% of scalp hairs are in anagen, 10% to 15% are in telogen, and only 1% to 2% are in catagen. With roughly 100,000 hairs on the average scalp, that means somewhere around 1,000 to 2,000 follicles are transitioning at any one time.
That said, newer research has challenged these long-accepted numbers. A study examining the back of the scalp in men with pattern hair loss found catagen hairs made up about 7.5% of follicles, while telogen accounted for only 3.5%. This suggests the catagen phase may be more common than previously thought, at least in certain populations and scalp regions. The traditional percentages were based on older counting methods, and more precise techniques are starting to revise the picture.
Why Catagen Matters for Hair Loss
Most hair loss doesn’t happen because catagen itself malfunctions. It happens because something pushes hair out of the growth phase too early, forcing it through catagen and into the resting and shedding phases ahead of schedule. Several factors can trigger this premature transition.
Hormonal shifts are a major driver. A hormone called DHT, which the body converts from testosterone, binds to receptors in the hair follicle and shortens the anagen phase while extending telogen. Over repeated cycles, this produces thinner, shorter hairs, which is the mechanism behind pattern hair loss in both men and women. Thyroid disorders (both overactive and underactive) can also push hairs prematurely out of growth, as can the drop in estrogen that comes with menopause.
Stress triggers a condition called telogen effluvium, where a large number of follicles exit anagen simultaneously. The stress hormone cortisol disrupts the hair cycle’s normal timing. Physical or emotional stress, major illness, surgery, or crash dieting can all set this off, typically causing noticeable shedding 2 to 3 months after the triggering event.
Chronic inflammation from autoimmune conditions or other systemic disorders can also force hairs from anagen into telogen prematurely, bypassing a normal growth timeline. Chemotherapy drugs work by targeting rapidly dividing cells, and because hair follicle cells divide faster than almost any other cells in the body, these medications can accelerate the transition out of anagen on a massive scale.
Nutritional Factors That Disrupt the Cycle
What you eat plays a real role in how long your hair stays in its growth phase. Iron deficiency is the most common nutritional deficiency worldwide, and it contributes to telogen effluvium. Zinc supports the protein synthesis and cell division that hair follicles depend on during anagen, and people with low zinc levels are more prone to shedding and brittle hair. Deficiencies in essential amino acids (the building blocks of the protein that hair is made of) are common across different types of hair loss.
Low levels of omega-3 and omega-6 fatty acids may increase the proportion of follicles sitting in the resting phase rather than actively growing. Even vitamins that are generally good for hair can cause problems in excess. Too much vitamin A can damage hair growth despite its role in stimulating follicle stem cells, and excessive vitamin E can lower thyroid hormone production, indirectly promoting hair loss.
How the Cycle Differs by Body Location
The catagen phase stays at 2 to 3 weeks no matter where the hair grows, but the other stages vary enormously. Scalp hair spends years in anagen, which is why it can reach shoulder length or beyond. Eyebrow hair has an anagen phase of just 4 to 8 weeks, and eyelash growth is similarly brief at 1 to 2 months. This is why your eyebrows and eyelashes never grow as long as the hair on your head.
The percentage of follicles in each phase also shifts by location. On the scalp, 80% to 90% of hairs are in anagen at any time. For eyebrows and eyelashes, that number drops to as low as 18% and tops out around 41%. This means a much larger share of brow and lash hairs are resting or transitioning at any given moment, which is why these hairs take longer to recover when they’re lost and why overplucking eyebrows can have lasting effects.
The total cycle from start to shed for a single scalp hair runs 2 to 8 years. For an eyelash, the full cycle averages about 4 months. For an eyebrow hair, 3 to 4 months. In every case, catagen occupies the same narrow 2 to 3 week window, a brief but essential reset that keeps the entire system running.