Finding hair on your pillow can be unsettling. But shedding is a normal part of how hair works. Each follicle on your scalp runs its own cycle of growth, rest and renewal. Understanding that cycle is the single most useful thing you can learn about hair, because it explains why hair falls, why it thins and why any genuine improvement takes months.
The follicle: a mini-organ that regenerates itself
A hair follicle is not a passive tube. It is a miniature organ that rebuilds itself again and again throughout life, cycling through phases of growth, regression and rest. Its behaviour is controlled by signalling families with names like Wnt, FGF, TGF-β and Sonic hedgehog, which tell the follicle when to grow and when to stop.
At the base of the follicle sits the dermal papilla, a cluster of specialised cells that acts as the control centre. Many hair-care studies, including research on minoxidil, placenta extracts and botanicals, measure effects on dermal papilla cells for this reason.
Phase 1: Anagen, the growth phase
Anagen is when the hair is actively made. Cells at the base of the follicle divide rapidly, building the hair shaft upwards.
The length of anagen largely decides how long your hair can grow. It is also the phase most affected by pattern hair loss, where anagen becomes progressively shorter.
Phase 2: Catagen, the transition
When anagen ends, the follicle enters catagen. Growth stops and the lower part of the follicle regresses through a tightly controlled process of programmed cell death. Catagen lasts about three to six weeks.
Phase 3: Telogen, the resting phase
In telogen, the follicle rests. The old hair, now called a club hair, stays anchored while the follicle prepares for a new cycle.
Shedding and renewal
At the end of telogen, the old club hair is released as a new anagen hair starts to grow beneath it. This is normal shedding. Because every follicle runs on its own schedule, you shed some hairs every day without your overall density changing.
When clinicians want to measure shedding objectively, they can use a standardised hair-wash test; shedding of more than 100 hairs in that test points towards telogen effluvium.
When the cycle goes wrong
Most hair loss is, at heart, a disruption of the hair cycle. The two most common patterns work in very different ways.
Androgenetic alopecia: a shrinking cycle
With each cycle, anagen gets shorter and telogen relatively longer, so the hair produced becomes shorter and finer. The condition is polygenic, involving many genes, with major contributions from the androgen receptor gene on the X chromosome and a region on chromosome 20. Low-grade inflammation around the follicle has also been described.
This is why pattern hair loss tends to look like gradual thinning rather than sudden shedding.
Telogen effluvium: a synchronised rest
In telogen effluvium, a trigger such as a high fever, illness, surgery, childbirth, crash dieting, certain medicines or major stress pushes a large number of follicles into telogen at the same time. Because telogen lasts months, the extra shedding appears later, typically two to four months after the trigger.
Acute telogen effluvium usually settles once the trigger is removed. Shedding that lasts more than six months is described as chronic. Telogen effluvium can also occur alongside androgenetic alopecia.
Seasons, scalp and lifestyle
The cycle is also influenced by things around it.
- Seasons. In a Swiss study of 823 healthy women, the proportion of resting hairs followed an annual rhythm and peaked in summer.
- Scalp health. Over 20 epidemiological studies link poor scalp condition, such as dandruff, to impaired hair, and in a treatment study the effects on hair were reversed when scalp condition was normalised.
- Oxidative stress. Reactive oxygen species from UV, smoking, pollution and scalp inflammation can affect the follicle and hair fibre.
- Nutrition. Iron, zinc, vitamin D and B vitamins all play roles in the follicle cycle, and genuine deficiency may be a modifiable risk factor for hair loss.
How treatments act on the cycle
The best-studied topical, minoxidil, works directly on the cycle: in animal studies it shortens telogen so resting follicles re-enter anagen earlier, and it may prolong anagen and enlarge follicles. This also explains the temporary shedding some people notice when they start: old resting hairs are released as new growth begins.
Other ingredients, from placenta extracts to green tea catechins, have been studied for effects on the dermal papilla and the timing of anagen, mostly in laboratory and animal research so far. These are interesting leads, but they are not equivalent to clinical proof in people.
Why patience is a scientific necessity
Put the numbers together: anagen lasts years, telogen lasts three to five months, and changes in the cycle take time to become visible. That is why reputable treatments describe results in months, not days. With minoxidil, for example, labelling states that results may appear from two months and some men need at least four months.
When to see a doctor
See a doctor if hair loss is sudden, patchy, painful, accompanied by scalp redness or scarring, or comes with other symptoms such as fatigue or weight change. These can signal conditions that need medical assessment, including nutritional deficiencies.
What are the three phases of hair growth?
Anagen (growth), catagen (transition) and telogen (rest). On the scalp, anagen lasts about two to five years, catagen three to six weeks and telogen three to five months.
Why does hair loss show up months after a stressful event?
Because of the length of telogen. A trigger pushes follicles into the resting phase, and the extra shedding appears about two to four months later.
Does pattern hair loss make hair fall out faster?
Not mainly. Pattern hair loss shortens the growth phase and miniaturises follicles, so hairs become progressively shorter and finer.
Is shedding more in summer normal?
It can be. A Swiss study of 823 women found the proportion of resting hairs peaked in summer.
Can you speed up the hair growth cycle?
Some treatments can influence it. Minoxidil shortens telogen in animal studies and may prolong anagen, but changes still take months to see.
