The active growing stage of hair is called the anagen phase. At any given time, about 90% of the hair on your scalp is in this phase, actively producing new cells and lengthening the hair shaft. The anagen phase is the longest part of the hair growth cycle, typically lasting two to seven years for scalp hair, and it’s the single biggest factor determining how long your hair can grow.
What Happens During the Anagen Phase
During anagen, cells in the hair bulb (the rounded base of the follicle buried in your skin) divide rapidly, stacking on top of each other to form the hair shaft. As new cells push upward, older cells harden, die, and become the visible strand of hair you see. This process also produces melanin, the pigment that gives hair its color.
Healthy hair grows about half an inch per month during this phase. That rate is remarkably consistent across most people, so the main variable in how long your hair can get isn’t growth speed. It’s how long your anagen phase lasts. Someone whose anagen phase runs seven years can grow hair past their waist. Someone with a two-year anagen phase will find their hair plateaus around 12 inches no matter what they do.
The Other Stages of the Hair Cycle
Hair doesn’t grow continuously. Each follicle cycles through three distinct phases independently of its neighbors, which is why you don’t shed all your hair at once.
- Catagen (transition phase): Lasting about two to three weeks, this is when active growth stops. The lower part of the follicle shrinks and detaches from its blood supply, forming what’s called a club hair.
- Telogen (resting phase): The follicle sits idle for roughly three months. The old hair stays loosely anchored while a new hair begins forming beneath it. Only about 9% of scalp hair is in this resting stage at any time. On body hair, however, 40 to 50% of follicles are resting, which is why body hair stays short.
In healthy people, the ratio of anagen hairs to telogen hairs on the scalp runs about 12:1 to 14:1. When that ratio shifts and too many hairs enter telogen at once, the result is noticeable thinning or shedding, a condition called telogen effluvium.
What Determines How Long Your Anagen Phase Lasts
Genetics is the primary driver. Your DNA sets the baseline duration of anagen for each body region, which is why eyelash follicles have an anagen phase of only a few months while scalp follicles can stay active for years. This is also why some people can grow very long hair effortlessly while others hit a natural ceiling.
Hormones play a significant role too. Androgens (hormones like testosterone and its derivative DHT) can shorten the anagen phase in genetically sensitive scalp follicles, gradually producing thinner, shorter hairs with each cycle. This is the mechanism behind pattern hair loss in both men and women. Thyroid imbalances and the hormonal shifts after pregnancy can also push follicles out of anagen prematurely.
Nutrition matters, though less dramatically than genetics. Iron deficiency, very low protein intake, and crash dieting can all cut the anagen phase short. Chronic stress triggers a similar effect by pushing a larger-than-normal percentage of hairs into telogen ahead of schedule.
Why the Anagen Phase Matters for Hair Removal
If you’ve ever been told you need multiple laser hair removal sessions spaced weeks apart, the anagen phase is the reason. Laser energy targets melanin inside the hair shaft, and that pigment connection to the follicle only exists during active growth. Research published in the journal Dermatologic Surgery found that laser treatment on anagen hairs caused them to rapidly shift into telogen and shed, while telogen hairs showed no response at all and stayed in place after treatment.
Because only a portion of follicles are in anagen at any appointment, you need several sessions to catch each follicle during its active window. The same principle applies to electrolysis and IPL treatments. Areas with a higher percentage of anagen hairs, like the scalp, respond more noticeably per session than areas like the legs, where more follicles are resting at any given time.
Signs Your Anagen Phase May Be Shortening
The clearest sign is that your hair no longer grows as long as it used to. If your ponytail has gotten thinner or your hair seems to stall at a shorter length than it reached a few years ago, your follicles may be spending less time in anagen. Increased daily shedding (well beyond the normal 50 to 100 hairs per day) is another indicator that hairs are cycling out of the growth phase faster than usual.
Miniaturization is a more subtle clue. When the anagen phase shortens progressively over many cycles, each new hair grows in finer and shorter than the last. You might notice wispy, almost transparent hairs around your temples or part line before outright thinning becomes visible. This gradual process is the hallmark of androgenetic hair loss and can begin years before noticeable density changes.