Your hair is not growing all at once. Right now, while you read this, some strands on your head are pushing out fresh length, a few are quietly winding down, and others are sitting still before they fall out and make room for the next one. This is the hair growth cycle, and once you understand how it works, a lot of the worry around shedding, length and "slow" growth starts to make sense.

This guide walks through the four phases in plain language, the honest truth about how fast hair actually grows, and what can knock the cycle off course. No marketing spin, just how the biology behaves on a normal head of hair.

The four phases of the hair growth cycle

Every hair on your scalp moves through a repeating loop. Scientists give the stages names borrowed from Greek, which is where the jargon comes from. Here they are without the mystery: anagen, catagen, telogen and exogen. Each follicle runs this loop independently, then starts again from the top.

Anagen: the phase that decides your length

Anagen is where the real work happens. During this stretch the follicle pumps out keratin and the strand gets longer, day after day, for years at a time. The length of your anagen phase is mostly written into your genetics, which explains why some people can grow hair to their waist while others find it never passes their shoulders no matter what they do.

If your anagen phase runs for two years, your hair simply has less time to grow before it moves on. If it runs for seven, you have a much longer window. This is also why eyebrows and eyelashes stay short. Their anagen phase lasts only a month or two, so they reach their full length quickly and then stop.

Catagen and telogen: winding down and resting

Once anagen ends, the follicle moves into catagen, a brief transition that lasts only a few weeks. Growth halts, the lower part of the follicle shrinks, and the strand becomes what is sometimes called a club hair, no longer connected to the blood supply that fed it.

Then comes telogen, the rest phase, which lasts around three months. The strand stays anchored in place but does nothing. Underneath it, a fresh hair has already started forming in the same follicle. The resting strand is essentially holding the spot until the new one is ready to take over.

Exogen: why you shed every day and stay perfectly normal

Exogen is the shedding step. The old, rested strand finally releases and drops out, often while you brush, wash or run your fingers through your hair. Losing somewhere between 50 and 100 strands a day is completely ordinary for most people.

Here is the part that puts a lot of minds at ease. Because every follicle is on its own clock, only a small slice of your hair is shedding at any given moment. The vast majority is still happily growing. You do not go bald from daily shedding because for every strand that leaves, another is already pushing through underneath. The cycle is staggered across hundreds of thousands of follicles, so the loss never lands all at once.

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How fast does hair actually grow

This is where a lot of marketing falls apart. On average, scalp hair grows about 1 to 1.5 centimetres a month, which works out to roughly 12 to 15 centimetres a year. That rate is set largely by your genetics, age and overall health, and it does not change much in response to most products.

When you see a claim promising to "make your hair grow faster," treat it with healthy suspicion. A serum cannot rewrite the speed your follicles produce keratin. What good care can do is help you keep the length you grow, which matters more than most people realise. If your hair grows 12 centimetres in a year but breaks off 10 along the way, you see almost no progress. Reduce that breakage and the same growth rate suddenly looks a lot more impressive.

• Genetics set your baseline growth rate and your maximum length.
• Age tends to slow growth gradually over the decades.
• General health, including iron levels and nutrition, supports a normal cycle.
• Hair care does not speed growth, but it protects the length you already have.

What pushes hair out of its cycle early

The cycle usually hums along quietly, but several things can shove a larger share of follicles into telogen ahead of schedule. When that happens, you get a noticeable wave of shedding a couple of months later, a condition called telogen effluvium. It looks alarming, though it is almost always temporary.

Common triggers include:

• Significant emotional or physical stress, which can interrupt the growth signal to many follicles at once.
• Illness or a high fever, particularly anything that runs your body down for a stretch.
• Childbirth, where the hormonal drop after pregnancy sends a large batch of resting hairs into shedding together.
• Crash diets and sudden weight loss, which starve follicles of the fuel they need.
• Iron deficiency, a frequent and often overlooked cause, especially in menstruating women.

The pattern with telogen effluvium is delay. The stress or illness happens, and the extra shedding shows up about two to three months later, once those follicles finish their rest phase and reach exogen. Because the trigger has often passed by then, the connection is easy to miss. The reassuring part is that the follicles are not damaged. Once the underlying cause settles, most of them return to anagen and start growing again. If heavy shedding carries on for more than six months, that is worth a conversation with your GP, since persistent loss can point to something like low iron or a thyroid issue that benefits from testing.

Breakage is a different problem from the cycle

Here is a distinction that gets blurred constantly. When your hair feels like it is not getting any longer, the cause is often not your growth cycle at all. It is breakage. A strand can be growing perfectly well at the root while snapping off partway down the length, so you never see the benefit of all that anagen.

Picture a single strand on a four year anagen run. To reach its full potential length, that fibre has to survive four years of brushing, heat styling, colouring, sun, friction against pillows and clothing, and every wash in between. That is a lot of wear for one strand to carry. The internal bonds that hold keratin together are what keep the fibre strong enough to last the distance.

When those bonds break down, through bleach, heat or repeated chemical processing, the strand weakens and eventually snaps. The follicle is doing its job, but the length never accumulates because the fibre keeps giving out before its anagen phase is finished. This is why bond health sits at the centre of long, healthy hair. It is not about growing faster. It is about keeping each strand intact long enough to reach the length your cycle is already trying to give you.

This is the science behind the K18PEPTIDE, which works at the level of the keratin chains inside the strand to support the bonds that hold a fibre together. Keep those bonds in good shape and your hair has a far better chance of completing its full anagen run without snapping along the way.

Working with your cycle, not against it

Once you understand the cycle, the goal shifts. You stop chasing impossible promises about speed and start protecting what you grow. Be gentle with wet hair when it is most fragile, ease off the hottest heat settings, give bleached and coloured hair extra support, and look after the basics like iron and nutrition that keep the cycle running normally.

We are building on this thinking with Future IQ, a science-led range launching in July that focuses on strand strength and long-term hair health. It is designed around the same principle covered here, that healthy bonds let each strand live out its full growth phase. More on that closer to launch.

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Your hair growth cycle is mostly out of your hands. Genetics decide the pace and the maximum length, and no product changes that. What you can influence is how much of that growth you actually keep, and that comes down to looking after the strength of every strand from root to tip.