Hair loss: common causes and what treatments actually work

While losing your hair can be distressing, it’s also very common.

The reasons for sudden or gradual hair loss can be wide-ranging. It isn’t automatically a cause for concern and can be temporary – due to lifestyle issues such as stress, illness or nutrient deficiencies, for example. But it can be stressful and upsetting, and it can impact your confidence.

Navigating treatment options is no picnic, either. From hair growth serums and tablets to caffeine shampoos, LED hair therapy and supplements – the range of hair loss treatments available is mind-boggling.

We asked hair loss experts for their insights on some of the most common causes, which treatments are backed by science, what to steer clear of, and the ones which might actually be worth a try.

One thing they all agreed on: it's important to understand what's triggering your hair loss first before splashing the cash on any products and treatments, so you don't waste time or money on something not suitable for you.

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Our hair loss experts

We got the lowdown from trichology experts, as well as from our in-house nutrition and supplements expert, Shefalee Loth:

• Neil Harvey is chairman of the Institute of Trichologists and has worked in the hair industry for nearly 40 years.

• Kate Holden is a trichologist and a qualified hairdresser. She’s also a registrant of the Institute of Trichologists.

• Shefalee Loth is a public health nutritionist with 20+ years at Which? and the NHS, delivering evidence-based food and nutrition insights to help you live better.

What causes hair loss?

A wide range of factors can cause hair loss and thinning. Some are preventable, but others are genetic (inherited). Equally, some are permanent, while others are temporary.

Some of the most common causes include genetics, stress, cancer treatment, weight loss, iron deficiency, tight hairstyles, illness, side effects of certain medications and hormonal fluctuations.

Understanding what's going on is the first step to getting the right treatment. It's sensible to visit your GP in the first instance to rule out any health issues that might be causing or contributing to your hair loss.

How do I know if my hair shedding levels are normal?

Some people may appear to shed more hair than others. It may be more noticeable, for example, if you have long or dark hair. What really matters is what's normal for you.

There are some key differences between normal shedding, excessive shedding and hair loss. Knowing them can help you spot when something isn’t quite right.

Neil Harvey has provided the following helpful breakdown to help you tell the difference:

• Normal shedding is part of the hair cycle: every day, approximately 50-100 hairs fall out and are replaced by new hairs growing back. Scalp coverage and hair density shouldn’t appear noticeably different.
• Excessive shedding is a temporary increase in hairs coming out all over the scalp, often noticed in the shower, brush, or on a pillow. It commonly shows up a couple of months after illness, high fever, surgery, major stress, rapid weight loss, or childbirth. The follicles can still produce hair, so fullness usually returns once the trigger has passed.
• Hair loss (alopecia) means growth is being interrupted or follicles are being damaged. Clues include a widening parting, gradual thinning, a receding hairline, distinct patches of hair loss, or no recovery over time. Causes include inherited pattern hair loss, autoimmune alopecia, medication or treatment effects, traction from tight styles, and inflammatory or scarring scalp disease.

Male hair loss vs female hair loss

‘Men tend to develop receding hair at the temples and thinning around the crown, whereas women more commonly notice diffuse thinning over the top of the scalp and a widening parting,’ explains Kate Holden.

Shared triggers include pattern hair loss (hereditary), stress-related shedding, nutritional deficiencies and hair loss linked to illness or medication.

How can stress and illness cause you to lose hair?

Some people may experience hair loss after a bout of illness or stress. 

‘A significant illness is a physical shock to the body,’ says Neil. ‘Fever, inflammation, reduced food intake, surgery, certain medicines and the stress of recovery can trigger hair follicles to stop active growth.’

This also happens after a particularly stressful event.

You may find that hair starts thinning around two to three months after illness or a stressful period. ‘The delay happens because hair stays in its ‘resting phase’ before it falls out,’ says Neil.

‘You might notice more hair in the hairbrush or in the shower, and some people experience a tingling or itchy scalp,’ says Kate.

This type of hair loss is usually temporary. Once the cause has settled, new growth generally starts back up again – unless there’s another underlying issue.

Do weight-loss jabs like Mounjaro cause hair loss?

Hair loss has been reported by some people using weight-loss jabs, but it’s not necessarily a direct side effect. 

‘They can be linked with increased shedding, but often it's the weight loss or reduced calorie and nutrient intake that is the trigger, rather than the medication itself,’ Kate explains.

‘I see this particularly when people lose weight rapidly or go very low carb. Making sure you're getting enough protein, iron and overall nutrition is important.’

This is also important for preventing loss of muscle mass while on the jabs. Find out more in our full guide to weight-loss injections and tablets.

Can menopause cause hair loss?

Yes. Fluctuating hormone levels during perimenopause and menopause can have a significant impact on your hair.

‘Falling oestrogen levels can cause hair to become finer and less dense, and can also make pattern hair loss more noticeable in women who are genetically predisposed to it,’ explains Kate.

‘Women may notice that their hair texture changes and products don't work the same as they used to,’ says Kate. 

Some forms of HRT can help, if this is right for you. However, hormones only form part of the picture. Kate adds that ‘other factors can also play a role, such as stress and general health’.

Best menopause supplements: we've analysed the scientific evidence behind active ingredients so that you know which are actually worth buying

Which vitamin deficiencies can cause hair loss?

‘Hair loss can be caused by many factors, but diet can play a major part,’ explains Which? principal researcher and nutritionist, Shefalee Loth. Iron and zinc are especially important for hair health.

‘An iron deficiency affects haemoglobin production, which in turn impacts oxygen transport around the body, including to hair follicles,’ explains Shefalee. 

‘Hair follicle cells are some of the fastest-dividing cells in the human body and need a continuous supply of oxygen. So, when iron levels drop, this process is affected and hair follicles are deprived of oxygen, resulting in weaker hair and slowed growth.’

When deprived of oxygen, hair follicles enter the ‘resting’ stage of the hair cycle, which can lead to hair loss a few months later.

‘Similarly, zinc is essential for cell repair and tissue growth,’ says Shefalee. A deficiency can lead to brittle hair and hair loss too.

Other important nutrients for hair health include vitamins C, D, biotin, folate (vitamin B12) and protein.

It's worth ruling out these causes before turning to expensive products and growth serums, when a basic supplement might do. 

Iron deficiency is one of the most common nutrient deficiencies in the UK, particularly among women, and it has broader health implications too, so it's worth getting checked out.

Best iron supplements – we’ve reviewed high street options from BetterYou, Holland & Barrett and more to uncover the best

Is seasonal hair shedding really a thing?

It’s not in your head. While not a major cause of hair loss, some evidence suggests shedding can increase at certain times of the year, says Kate.

‘Late summer and early autumn seem to be a peak time for seasonal shedding,’ she tells us. So, don't immediately assume the worst if you notice an uptick in hair loss.

But equally, Kate adds: ‘If someone has a significant or prolonged increase in shedding, I wouldn’t simply put it down to the time of year.’ If you have concerns, it's worth getting checked out.

Which hair loss treatments really work, and which ones don’t

This really depends on the type of hair loss you have. Our experts all agreed it's crucial to identify the cause first for the greatest chance of seeing long-term improvement. 

Too often, they warn, people start with a product first, before identifying the root cause of their hair loss. This can lead to money, time and energy being spent on treatments that may not be right for your needs.

Here's what our experts said about popular hair loss treatments:

Does minoxidil work for hair loss?

Our experts agree that minoxidil is one of the best treatments for male and female pattern hair loss.

It’s available as low-dose, prescription-only oral tablets, as well as over-the-counter topical treatments (such as Regaine), designed to be applied directly to the scalp to help encourage blood supply to hair follicles. 

Kate and Neil highlight how minoxidil has some of the strongest evidence for helping to improve pattern hair loss. ‘It can slow loss and improve density, but it takes six to 12 months and must be continued to maintain its benefit,’ says Neil.

What are the side effects of minoxidil?

There are also some side effects to bear in mind, depending on the type and dosage.

‘Minoxidil can cause some initial shedding, scalp irritation and greasiness,’ says Kate.

An increase in your hair shedding cycle can come as a surprise for many people, but it normally settles within the first six weeks of treatment.

Topical minoxidil can potentially also cause other possible side effects, including irritation, dandruff and unwanted hair growth.

According to the NHS, oral minoxidil is generally well tolerated, particularly if you’re on a low dose. There are more potential side effects if you’re on a higher dose, though, including palpitations, chest pain, dizziness, rashes and more.

It also many not suitable if you have health issues like high blood pressure or if you’re on certain types of medication. It should be avoided if you’re pregnant or breastfeeding, too.

Speak to your pharmacist, GP or a health professional before starting minoxidil treatment to chat through any concerns you may have. It’s also important to buy via reputable retailers rather than unvetted sellers on social media or online marketplaces (and the tablets should only be bought via a registered pharmacy).

Does finasteride work for hair loss?

Finasteride (also known as Proscar and Propecia) is another common treatment for male pattern hair loss. It's available via private prescription as tablets.

‘Finasteride is one of the most effective evidence-based treatments for male pattern hair loss,’ says Neil. ‘It’s not a general remedy for hair shedding from illness, stress, or nutritional deficiency though.’

Finasteride helps to reduce hair loss by stopping testosterone from turning into another hormone called dihydrotestosterone (DHT). DHT can stop your hair from growing.

Improvements can be seen between three and six months, according to the NHS. However, it requires careful monitoring. ‘Finasteride can slow further loss but needs to be assessed by a clinician regarding possible sexual and mood side effects,’ Neil cautions.

Side effects of finasteride are estimated to affect more than one in 100 people, according to the NHS. These include erectile dysfunction and loss of libido. In rare cases, it can cause breast cancer and depression.

‘UK guidance was strengthened in 2026,’ says Neil. ‘Discuss personal and family mental health history, fertility plans, other medicines, and side effects with your prescriber before starting.’

Again, it's very important to only get it from a reputable pharmacy or GP to ensure it's appropriate for you and you are taking it safely. 

Can supplements help with hair loss?

Potentially. However, only if you have a deficiency in a key nutrient like iron. ‘Supplements are useful when someone has a genuine deficiency, but they aren't a solution for every type of hair loss,’ says Kate. ‘As a trichologist, I look at the whole picture.’

‘If you're experiencing hair loss, I recommend speaking to your doctor before taking supplements,’ says Shefalee. ‘They may request blood tests to see whether the cause is identifiable.’

‘If nutritional deficiencies are identified from a blood test, your GP will be able to advise you on dietary changes and supplements if appropriate. Or you could speak to a dietitian or registered nutritionist.’ 

Having a blood test in the first instance could help you save money in long-term and find the supplements best suited for your needs. 

Can biotin supplements help your hair grow?

Often touted as the ‘beauty vitamin’, biotin (also known as vitamin B7) can be found in many supplements with claims that it can support hair health. This is because biotin helps produce keratin, which is the main protein in hair.

However, there is no strong evidence that biotin supplements can increase hair growth, and it's not an approved claim on the UK Health claims register. Look carefully and you'll see the wording is usually around supporting normal maintenance, rather than boosting anything. 

Shefalee says: ‘We need around 50mcg of biotin a day – a tiny amount – and it's found in plenty of foods, including eggs, salmon, pork, beef, nuts and seeds, sweet potatoes, avocados, peanut butter, soya beans, brown bread and oats. As a result, deficiencies are rare and most people don't need supplements.’

‘Biotin supplements often contain more than the daily amount needed, but it's a water-soluble vitamin so your body can't retain it, and excess amounts are excreted in urine.’

In other words, there’s a good chance you're flushing any money spent on high-strength biotin supplements down the toilet. It could also impact blood test results. Find out more in our full story on biotin beauty supplements.

Do hair growth serums work?

Hair growth serums are big business. From high street to high-end, The Ordinary to Kérastase, they’ve seen a surge in popularity. But can any of them actually help with hair loss?

Our experts say it's a bit too early to tell from an evidence-based perspective:

‘Some ingredients have promising early research, and they have a place for people who want to improve their hair and scalp health or support their hair after a period of temporary stress-related hair loss,’ says Kate.

‘However, they simply don't have the same level of evidence as established treatments such as minoxidil.’

‘Peptides, caffeine and certain plant extracts are interesting, and my general take is that they may help and are unlikely to do any harm, so they can be a good first step.’

If you’re looking for a topical treatment, however, Neil believes that minoxidil is the gold standard. ‘A 2% or 5% leave-on solution/foam has substantially stronger evidence for pattern thinning than cosmetic 'growth serums'. It supports growth and helps maintain density – but needs consistent use for months and its benefit fades if stopped.’

Until more research is conducted, he’s dubious about the lofty promises of certain high street tinctures. ‘For peptides and branded blends, I’d be cautious. They may improve scalp comfort, hair-fibre quality, and sometimes the look of density, but independent, high-quality evidence of meaningful follicle regrowth is limited.’

If you're interested in trying a hair growth serum, key brands are generally readily available in supermarkets and pharmacies, as well as online. We've rounded up some of the most popular hair growth serums containing ingredients such as peptides and caffeine below. 

Please note that we haven't tested or reviewed these products, so inclusion here doesn't constitute a recommendation.

Can rosemary oil help hair growth?

Rosemary oil peaked in popularity as a hair booster on social media a couple of years ago, becoming the viral 'go-to' home remedy for hair loss. 

There isn’t a lot of data to back up its claims for hair growth. Those who are fans often cite the de-stressing ritual of massaging it into their scalp as beneficial for circulation.

Is that enough, though?

‘I think the hype has gone further than the evidence, and I find lots of people don't stick with it because of how oily it makes their hair, and it can irritate your scalp too,’ says Kate. ‘I wouldn't recommend rosemary oil as a replacement for an evidence-based treatment, particularly for significant hair loss.’

Neil expresses similar concerns: '"Natural" ingredients such as rosemary can also irritate or trigger contact dermatitis,’ he cautions.

Does caffeine shampoo help hair loss?

Caffeine shampoos, such as Alpecin and Plantur 39, have cult followings because they claim to re-energise roots, help hair appear fuller and offer an entry-level price point (around £8-£12).

But can they make significant changes to hair loss? ‘There is some research around caffeine and hair growth, but we have to remember that shampoo is rinsed off quite quickly,’ says Kate.

‘I wouldn't rely on a caffeine shampoo to treat significant hair loss, although there's no reason it can’t form part of a general haircare routine.’

Neil is also keeping an eye on caffeine in leave-on products. ‘Topical caffeine is the non-prescription ingredient I’d view as potentially promising, but not proven enough to put beside minoxidil,’ he says.

‘Recent reviews find small favourable studies and good tolerability, yet many trials lack rigorous controls or use poorly defined formulations. It may be a reasonable add-on if the scalp tolerates it, but not a replacement for diagnosis or established treatment.’

If you’re interested in trying a caffeine shampoo, you can find them at most supermarkets, pharmacies and online. We've rounded up some of the most popular caffeine shampoos below. 

Please note that we haven't tested or reviewed these products, so inclusion here doesn't constitute a recommendation.

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Can LED light therapy help hair growth?

The NHS says UV light treatment is a potential treatment for hair loss. It involves shining ultraviolet light on areas of concern to encourage regrowth, but it comes with associated risks and is usually done only in certain circumstances for conditions such as alopecia and psoriasis.

More recently, LED light therapy hair devices have emerged as a new treatment option, known as LLLT (low-level light therapy). These use safer red LED light to stimulate hair growth.

Both Kate and Neil agree that they can be effective for certain cases.

‘I recommend using low-level light therapy for mild pattern hair loss or as a supplementary treatment for other types of hair loss, although the results tend to be fairly modest,’ says Kate.

‘The key is consistency, as these devices need to be used regularly for several months. I'd also look for a device with proper clinical evidence behind it.’

Neil also highlights that there’s evidence to show that low-level light therapy can improve hair density and shaft thickness in male and female pattern hair loss. ‘It’s non-invasive and generally well tolerated, but results are gradual and variable.’

He recommends it as a helpful, low-risk add-on, especially for those who can’t use prescription treatments. It isn't cheap though. 

Before buying one, he advises checking that the device is intended for hair loss and has realistic before-and-after evidence.

Where to buy LED hair masks

LED hair masks are relatively new to the market. However, they are becoming more widely available at established health and beauty retailers like Cult Beauty and Selfridges. Prices start from around £300.

We've rounded up some of the most popular LED hair growth masks below. 

Please note that we haven't tested or reviewed these products, so inclusion here doesn't constitute a recommendation.

• CurrentBody LED Hair Growth Helmet - 620-660nm red light therapy emitted from 120 red light LEDs, SQUIRREL_TEXT_50029923 
• Higherdose Red Light Hat - uses 650nm red light. Its LED bulbs are tucked inside a cotton cap, SQUIRREL_TEXT_50029924 
• Beauty Pie H-Wave LED Hair and Scalp Treatment - powered by 125 LED lights that deliver 655nm red light therapy inside a baseball cap, available from Beauty Pie (£332)
• Nooance Laser and LED Hair Helmet - emits 650nm wavelength red light through a combination of 82 low-level lasers and 200 LEDs, available from Selfridges (£945)