Your Hair Grows for 2 to 7 Years, Then Rests for 3 Months. That Is Why Length Has a Ceiling
Every hair on your head is on a schedule, and the schedule is why your hair has a maximum length that no product can change. The hair cycle has three phases. Anagen is the growth phase, and it lasts 2 to 7 years, with about 90 percent of your scalp hairs in it at any given moment. Catagen is the transition phase, and it lasts 2 to 3 weeks, during which the follicle shrinks and detaches from the blood supply. Telogen is the resting phase, and it lasts about 3 months, with 10 to 15 percent of your scalp hairs in it, waiting to shed and be replaced by a new anagen hair. The cycle repeats for the life of the follicle, and the length of your anagen phase is the ceiling on how long your hair can grow. Hair grows about 0.35 millimeters a day, about 1 centimeter a month, about 15 centimeters a year. Multiply that by your anagen length and you get your maximum hair length. Someone with a 2-year anagen phase caps out around 30 centimeters. Someone with a 7-year anagen phase can reach a meter. That difference is genetic, and it is why some people can grow waist-length hair and others cannot, no matter what they put on it.
The numbers are consistent across sources. The American Academy of Dermatology says the average person sheds 50 to 100 hairs a day, and that shedding is the telogen hairs leaving on schedule, not a sign of hair loss. Telogen effluvium, the diffuse shedding that follows a trigger, starts 2 to 3 months after the trigger, because that is how long the telogen phase lasts: the hairs that were pushed into telogen by the illness, the surgery, or the stress take three months to shed, which is why the shedding feels delayed and disconnected from the event that caused it. The anagen phase is where the growth happens, and it is also where the vulnerability is: chemotherapy, severe illness, and crash dieting can push anagen hairs into telogen early, which is why the shedding after a major event is so dramatic. The follicle is not dead. It is resting, and it will grow again, on the schedule of the cycle, not on the schedule of your anxiety.
What the cycle means for your routine
The cycle sets the timeline for everything you do to your hair. A treatment that claims to grow hair in a month is lying, because a month of anagen growth is one centimeter, and a new anagen hair takes weeks to emerge from the follicle after the telogen hair sheds. Minoxidil, the treatment with the strongest evidence for pattern hair loss, takes three to six months to show visible results, because that is how long it takes for enough follicles to shift into anagen and grow enough length to be visible. A supplement that claims to work in two weeks is selling a calendar, not a cycle. The practical implication is patience, and it is the hardest part of hair care, because the cycle is slow and the marketing is fast. If your hair is shedding more than 100 hairs a day for more than a few weeks, or if the shedding started two to three months after an illness, a surgery, or a major stress, see a dermatologist, because the cause is usually identifiable and often treatable. The cycle is not a mystery. It is a schedule, and once you know it, the claims that violate it are easy to spot.
Keep reading: Seasonal Shedding in Autumn: Why the Drain Fills Up Every October, Postpartum Hair Shedding: The Timeline, and When It Stops Being Normal, and Telogen Effluvium: The Shedding That Starts Two Months After the Illness cover the nearby cases in this series.
Frequently asked questions
How long does the anagen growth phase last?
Anagen, the growth phase, lasts 2 to 7 years, and about 90 percent of your scalp hairs are in it at any given moment. The length of your anagen phase sets the maximum length your hair can reach, because hair grows about 0.35 millimeters a day, or about 1 centimeter a month.
How many hairs do you shed per day normally?
The American Academy of Dermatology says the average person sheds 50 to 100 hairs a day. That shedding is the telogen hairs leaving on schedule, not a sign of hair loss. Shedding above that range for more than a few weeks is worth seeing a dermatologist about.
Why does hair shedding start months after an illness?
Telogen effluvium shedding starts 2 to 3 months after the trigger, because that is how long the telogen resting phase lasts. The hairs pushed into telogen by the illness, surgery, or stress take three months to shed, which is why the shedding feels delayed and disconnected from the event.
How long does it take for a hair treatment to work?
Three to six months for visible results, because that is how long it takes for enough follicles to shift into anagen and grow enough length to be visible. A treatment that claims to grow hair in a month is lying, because a month of anagen growth is about one centimeter.