If your hair will not grow, the cause is rarely the hair itself. In almost every case growth has stalled because something upstream has pushed your follicles out of their active growing phase too early, or slowed the rate at which new hair is made. The most common medical reasons are thyroid imbalance, iron or vitamin deficiency, hormonal shifts such as PCOS, menopause and the postpartum period, stress related telogen effluvium, scalp conditions, certain medications, and inherited pattern hair loss. Working out which one applies to you, ideally with a GP, is the single most important step, because the fix is almost always to treat the underlying trigger rather than to chase the hair.

How does hair actually grow, and how fast?

Every follicle runs on a repeating cycle with distinct phases. The growth phase (anagen) lasts roughly two to seven years and is when the hair actively lengthens. A short transition phase (catagen) of a couple of weeks follows, then a resting phase (telogen) of around three months, after which the old hair is released (shedding, or exogen) and a new hair begins to grow in its place.

On average scalp hair grows about 1cm each month, or roughly six inches a year. The maximum length you can reach is set mainly by how long your anagen phase lasts, and that is largely written into your genes. This is why some people can grow hair to their waist while others find it never passes their shoulders, even with perfect care. You carry somewhere between 100,000 and 150,000 follicles on your scalp, and losing 50 to 100 hairs a day is completely normal, because at any moment a share of your follicles is simply resting.

Is your hair really not growing, or is it breaking?

Before assuming a medical cause, it helps to separate three different problems, because they have different fixes.

• Slowed or stalled growth: new hair is coming through more slowly, or a large share of follicles has been pushed into the resting phase at once. This is where most medical causes sit.
• Excess shedding: you are still growing hair, but you are losing it faster than usual, so overall density drops. Telogen effluvium is the classic example.
• Breakage: the hair grows normally at the root but snaps partway along the strand, so it never seems to gain length. Heat, bleach, tight styling and over processing are the usual culprits here rather than anything medical.

A quick test: if you gently tug a small section and several hairs come away from the root with a tiny white bulb, that points to shedding. If strands snap in the middle and feel dry and rough, that points to breakage. If neither happens but length has plateaued for years, that is more likely your natural terminal length. If you are unsure, a GP or trichologist can tell the difference quickly.

What are the medical reasons your hair will not grow?

1. Thyroid imbalance

The thyroid gland sets your metabolic pace, and hair follicles are highly sensitive to it. Both an underactive thyroid (hypothyroidism) and an overactive one (hyperthyroidism) can push follicles into the resting phase, thin the hair evenly across the scalp, and slow regrowth. Tell tale extra signs include unexplained weight change, fatigue, feeling unusually cold or hot, and changes to your mood or periods. A simple blood test can confirm it, and hair usually recovers once thyroid levels are corrected. Our guide to thyroid related hair loss and whether it is reversible covers this in more detail.

2. Iron, ferritin and other nutrient deficiencies

Hair is one of the first places the body economises when a key nutrient runs low, because it is not essential for survival. Low iron, and specifically low ferritin (your stored iron), is one of the most common findings in women with diffuse thinning. Low vitamin D, vitamin B12, zinc and simply not eating enough protein can all push follicles into rest and slow the rate at which new hair is built.

The important point is that supplements only help when you are genuinely deficient. Taking high dose biotin or iron when your levels are already normal will not make hair grow faster, and excess iron can be harmful, so it is worth asking your GP for a blood test rather than guessing. A balanced diet with lean protein, leafy greens, eggs, oily fish, nuts and pulses covers most bases.

3. Hormonal shifts: PCOS, menopause and postpartum

Hormones are one of the biggest levers on the hair cycle. Polycystic ovary syndrome (PCOS) can raise androgen levels and gradually thin hair at the crown, while also causing acne or irregular periods. Around menopause, falling oestrogen changes the balance so that hair grows more slowly, feels finer and sheds more. After giving birth, the drop in pregnancy hormones triggers a temporary but sometimes dramatic shed a few months later that almost always recovers on its own. If this sounds familiar, read our guides to PCOS hair loss and what counts as normal hair loss for a woman after 40.

4. Telogen effluvium (stress, illness and surgery)

Telogen effluvium is a temporary but often alarming shed that happens when a large batch of follicles is pushed into the resting phase together. Common triggers include a high fever or infection (including COVID-19), major surgery, a serious emotional shock, a crash diet, or coming off certain medicines. The shed usually shows up two to three months after the trigger, which is why the cause is easy to miss.

The good news is that telogen effluvium is almost always self limiting: once the trigger passes, the follicles wake up and regrowth follows over the next six to twelve months. Managing stress through sleep, movement and calming routines genuinely helps here, because ongoing stress can keep the shed going. Our article on what causes telogen effluvium, its timeline and recovery walks through what to expect.

5. Scalp conditions

A follicle sitting in an inflamed or diseased scalp cannot do its best work. Seborrhoeic dermatitis (severe dandruff) and scalp psoriasis create flaking, itching and inflammation that can weaken growth. Fungal infections such as tinea capitis, more common in children, cause scaly patches and broken hairs. Alopecia areata is an autoimmune condition that produces sudden smooth, round bald patches. These conditions need a proper diagnosis, because the treatment is specific to each one, so a GP or dermatologist is the right first stop rather than a shop shelf.

6. Medications and medical treatments

A number of medicines list hair thinning as a side effect. Chemotherapy is the best known, and its hair loss is usually temporary. Others include some anticoagulants (blood thinners), certain antidepressants, beta blockers, high dose vitamin A derivatives (retinoids), and some hormonal treatments. Crucially, you should never stop or change a prescribed medicine on your own to protect your hair. Speak to the doctor who prescribed it: there is often an alternative, and in many cases the hair recovers once treatment ends.

7. Androgenetic alopecia (genetic pattern hair loss)

The most common cause of long term thinning is inherited pattern hair loss, known as androgenetic alopecia. It affects both men and women, and it works by gradually shrinking (miniaturising) follicles that are sensitive to a hormone called DHT, so each new hair grows finer and shorter until the follicle eventually stops. In men it usually shows as a receding hairline and crown thinning; in women it tends to be a widening parting with overall thinning. It is progressive, so early, clinician guided action gives the best result.

Temporary versus longer term causes at a glance

What actually helps your hair grow?

It helps to separate the options by how strong the evidence is, so you can spend your effort where it counts.

• Strong evidence, treat the cause: correcting a thyroid problem, replenishing low iron or vitamin D, and managing a hormonal condition such as PCOS all allow the hair cycle to return to normal. For genetic pattern loss, treatments such as minoxidil are established, but they should be started with a pharmacist or doctor rather than self prescribed.
• Sensible cosmetic and lifestyle support: a gentle scalp care routine, a protein rich balanced diet, reducing heat and tight styling, and managing stress all support the hair you have and reduce breakage. They will not override a medical cause, but they remove the everyday factors that make things worse.
• Limited evidence, low risk: scalp massage, rosemary and various oils, and general supplements may help some people at the margins, but the results are modest and inconsistent, so treat them as extras rather than a cure.

Gentle everyday scalp care: Grow Me® Shampoo

If you want a kind, sulfate free base for your routine while you deal with the underlying cause, our Grow Me Hair Growth Shampoo (£14.95) cleanses without stripping and includes biotin, caffeine, rosemary and niacinamide to help hair look and feel fuller. It is a cosmetic support for healthy looking hair, not a treatment for any medical condition, so pair it with proper medical advice where a cause is suspected.

Vegan, made in the UK, and part of a range with over 5 million bottles sold since 2012.

When should you see a GP or dermatologist?

Everyday thinning and slow growth are common and often harmless, but some signs deserve a professional opinion. Book an appointment if you notice any of the following:

• Sudden or rapid hair loss, or hair coming out in clumps.
• Smooth, round bald patches appearing on the scalp or beard.
• A scalp that is sore, scaly, red, intensely itchy or scarring.
• Thinning alongside other symptoms such as tiredness, weight change, irregular periods or new acne.
• Hair loss in a child.

A GP can arrange the right blood tests and examine your scalp, then refer you to a dermatologist or trichologist if needed. Getting a diagnosis early gives you the best chance of a full recovery, especially for conditions that are progressive.

Everyday habits that support healthy growth

• Eat enough protein and a varied diet rich in iron, zinc and vitamins.
• Stay hydrated and prioritise sleep, which is when much of your body repair happens.
• Use heat tools less often and always with a heat protectant.
• Avoid tight ponytails, braids and extensions that pull at the roots (traction).
• Massage your scalp for a minute or two while shampooing to support circulation.
• Be patient: because hair grows about 1cm a month, real progress takes several months to show.

Frequently asked questions

Why will my hair not grow past a certain length?

This is usually your natural terminal length, set by how long your genetically determined growth phase lasts. If the hair is snapping rather than plateauing, breakage from heat, colour or tight styling is the more likely reason, and gentler handling helps.

Is it normal to lose hair every day?

Yes. Losing 50 to 100 hairs a day is completely normal, because a share of your follicles is always resting and releasing old hairs. Losing noticeably more than that, or seeing thinning, is worth investigating.

Can a vitamin deficiency really stop hair growing?

It can slow it. Low iron, ferritin, vitamin D, B12 and zinc are all linked to increased shedding and slower growth. Supplements only help if you are genuinely deficient, so a blood test first is wise rather than guessing.

How long does hair take to grow back after shedding?

For a temporary shed such as telogen effluvium or postpartum shedding, regrowth usually begins within a few months of the trigger passing, with visible improvement over six to twelve months.

Can stress stop my hair from growing?

Significant physical or emotional stress can push follicles into their resting phase early, causing a shed a couple of months later. Managing stress and allowing time usually lets growth return.

Does shampoo affect hair growth?

Shampoo will not override a medical cause, but a gentle, sulfate free shampoo keeps the scalp clean and comfortable and reduces breakage, which supports the hair you have. Harsh, stripping products can make dryness and breakage worse.

Can hair loss from medication be reversed?

Often yes, once the treatment ends or is changed by your doctor. Never stop a prescribed medicine yourself; speak to your prescriber, who can advise on alternatives.

When is hair loss a sign of something serious?

See a GP promptly if loss is sudden or patchy, if your scalp is sore, scaly or scarring, or if thinning comes with fatigue, weight change or irregular periods, as these can point to a treatable underlying condition.

Understanding why your hair will not grow is the first real step to fixing it. Most causes are diagnosable and many are reversible once you know what you are dealing with, so pair good everyday scalp care with the right medical advice, and give it time.