The anagen phase is the active growth stage of the hair cycle, when cells in the hair follicle divide rapidly and produce new hair. On your scalp, this phase lasts anywhere from two to eight years, which is why head hair can grow so long compared to hair on other parts of your body. At any given time, roughly 85% to 90% of your scalp follicles are in anagen, with the rest in transitional or resting stages.
How the Growth Cycle Works
Every hair follicle on your body cycles independently through three main phases: anagen (growth), catagen (transition), and telogen (rest). During anagen, cells at the base of the follicle divide at a remarkable rate, building the hair shaft from the bottom up and pushing it outward through the skin. This is the only phase during which your hair is actually getting longer.
Once anagen ends, the follicle enters catagen, a brief transition period lasting a couple of weeks. The lower part of the follicle shrinks, and the hair detaches from its blood supply. Then comes telogen, a resting phase that lasts a few months before the old hair sheds and a new anagen phase begins. Only about 1% to 2% of your scalp follicles are in catagen at any moment, while 10% to 15% are in telogen.
What Happens Inside the Follicle
The engine of anagen is the dermal papilla, a cluster of specialized cells at the very base of the follicle. These cells release growth signals that trigger surrounding stem cells to start multiplying. One of the most important signals is a growth factor called IGF-1, which does several things at once: it drives cell division, delays programmed cell death, and keeps the follicle in its growth phase longer.
IGF-1 also boosts the production of another signaling molecule, VEGF, which stimulates the formation of tiny blood vessels around the follicle. This expanded blood supply delivers the oxygen and nutrients that rapidly dividing cells demand. As anagen winds down and the follicle transitions to catagen, VEGF levels drop and the blood vessel network around the follicle shrinks. This vascular cycle is part of why healthy circulation matters for hair growth.
How Fast Hair Grows During Anagen
Scalp hair grows an average of 0.5 to 1.7 centimeters per month during anagen, roughly 0.2 to 0.7 inches. That works out to about 6 to 20 centimeters (2.4 to 8 inches) per year, depending on the individual. Genetics, age, hormones, and nutrition all influence where you fall within that range.
The maximum length your hair can reach is determined almost entirely by how long your anagen phase lasts, not by how fast your hair grows per month. Someone whose scalp follicles stay in anagen for eight years can grow hair past their waist. Someone with a two-year anagen phase will find their hair plateaus at shoulder length or shorter, even if their monthly growth rate is identical.
Why Body Hair Stays Short
The reason your eyebrows never grow to your chin is simple: their anagen phase lasts only two to three months. Eyelashes follow a similar short cycle. Arm and leg hair also have brief growth windows, typically a matter of months rather than years. Each follicle is genetically programmed for a specific anagen duration based on its location, which is why different parts of your body have such different hair lengths even though the growth mechanism is the same everywhere.
Factors That Shorten or Disrupt Anagen
Several things can cut the anagen phase short or damage follicles mid-growth, leading to noticeable hair loss. The medical term for hair loss during the growth phase is anagen effluvium, and it looks different from the more common shedding that happens when too many hairs enter the resting phase at once.
Chemotherapy is the most well-known cause. Because cancer drugs target rapidly dividing cells, they hit hair follicle cells especially hard. The rate of hair loss varies by drug type. Antimicrotubule agents cause hair loss about 80% of the time, while certain antimetabolites trigger it in only 10% to 20% of patients. Hair loss from chemotherapy typically begins within weeks of starting treatment and can affect the scalp, eyebrows, eyelashes, and body hair.
Other triggers include heavy metal exposure (thallium, mercury, and cadmium are among the worst offenders), severe protein-energy malnutrition, autoimmune conditions like alopecia areata, and radiation. Some less obvious medications have also been linked to anagen effluvium, including drugs used for gout, tuberculosis, and organ transplant rejection. The good news is that in most of these cases, once the triggering factor is removed, follicles re-enter anagen and hair regrows.
What Keeps Anagen Healthy
Because the anagen phase depends on rapid cell division, anything that supports cellular health tends to support hair growth. Adequate protein intake matters because hair is made almost entirely of a protein called keratin. Iron, zinc, and B vitamins all play roles in the metabolic processes that fuel follicle activity. Deficiencies in any of these can push follicles out of anagen prematurely.
Blood flow to the scalp also plays a direct role. Since VEGF-driven blood vessel growth is what keeps active follicles nourished, anything that improves scalp circulation can help sustain the growth phase. This is part of why scalp massage has shown modest benefits in some small studies, and why conditions that impair circulation can contribute to thinning hair.
Hormones are another major influence. Androgens (the group of hormones that includes testosterone) can shrink follicles on the scalp over time, progressively shortening their anagen phase. This is the mechanism behind pattern hair loss in both men and women: follicles don’t die, but their growth phase gets shorter and shorter with each cycle, producing thinner and shorter hairs until the visible hair is barely noticeable.