How does the hair growth cycle work?
Your hair growth cycle is the constant process of your hair replacing itself with new hair. The average human head has about 100,000 hairs2, and every strand moves through its own cycle independently – which is why hair falls out at different times, rather than all at once.
Before we get into what causes hair fall, read on to first understand how your hair growth cycle works.
The growth phase
This is when your hair is actively growing, also known as the anagen phase. During this time, the hair follicle is fully active and firmly connected to your scalp3. Around 85 to 90% of scalp hairs are in this phase at any given time, and it can last anywhere from two to seven years, depending on genetics, age, and gender3.
The transition phase
Also called the catagen phase, this is a short transitional period that typically lasts two to three weeks and signals the end of active growth3. During this time, the hair follicle begins to shrink, cutting the hair off from its blood supply and preparing it to enter the next phase3.
The resting phase
Known as the telogen phase, this is when your hair is still attached to your scalp but is no longer growing. Instead, it's "resting" while the follicle prepares to start a new growth cycle3. This phase typically lasts two to four months, and around 10 to 15% of your hair is in this phase at any given time3.
The shedding phase
Referred to as the exogen phase, this is when the hair is finally released from the follicle and sheds, making way for new hair already growing beneath it3. As the new strand grows in, it gradually pushes the old one out3. This is a completely normal part of the hair cycle and once a hair sheds, the cycle starts all over again3.
Hair fall vs hair breakage: how can you tell the difference?
Hair fall and breakage can look similar, but they happen for very different reasons.
Hair fall is the shedding of a hair strand from the root, while breakage happens when a weakened strand snaps somewhere along the hair shaft. Look closely, though, and you'll notice the difference:
Feature | Hair fall | Hair breakage |
The root | Features a small white or pale bulb at one end. | No bulb: the end may look blunt, frayed, or jagged. |
Strand length | Usually close to your overall hair length. | Varied and uneven, often much shorter than the rest of your hair. |
When it happens | Often noticed daily, especially in the shower or while brushing your hair. | Often increases when handling, styling, or detangling hair. |
What are the most common hair fall causes?
Hair fall often happens when the natural hair growth cycle is disrupted, causing more strands than usual to enter the shedding phase at once.
Below, we explain what causes hair fall, from genetics and hormones to stress, nutrition, and styling habits, so you can better understand what may be affecting your hair.
Genetics and pattern thinning
Genetics are the most common hair fall cause. If your follicles are sensitive to hormones – something you inherit, not something you cause – they shrink a little more with each cycle4.
Smaller follicles can only produce smaller hair, so it grows back finer, shorter, and eventually harder to see4. Because it happens so gradually, a doctor can help confirm that your hair fall is genetic and talk you through your available options.
Stress or major changes to the body
Significant stress on your body – such as illness, surgery, rapid weight loss, or major life events – can increase hair fall4. This is because stress raises cortisol levels (the stress hormone), which can disrupt the normal hair growth cycle and push more hairs into the shedding phase earlier than usual4.
Hormonal changes
Childbirth and menopause both bring hormonal shifts that affect hair fall. Oestrogen – which rises during pregnancy – keeps hair in its renewal phase for longer (which is why hair grows faster during pregnancy)5. After birth, oestrogen levels drop quickly, and those hairs shed all at once5. Menopause works in a similar way: as oestrogen and progesterone decline, the renewal phase shortens and regrowth slows6.
Nutritional changes or deficiencies
Hair follicles are some of the most metabolically active cells in your body, which means what causes hair fall can sometimes come down to your diet7.
Your hair needs a constant supply of protein, iron, zinc, and key vitamins to support growth7. When your diet falls short on these nutrients, your body shifts into survival mode, redirecting resources to vital organs first and leaving hair growth low on the priority list.
Medications, rapid weight loss, or GLP-1-related changes
Rapid weight loss, significant dietary changes, and some medications can place stress on the body and affect the hair growth cycle. In some cases, this can trigger a temporary increase in shedding known as telogen effluvium8. People taking GLP-1 medications may also notice hair shedding if weight loss occurs quickly or overall nutrient intake decreases8.
If this applies to you, speak with a healthcare professional for personalised guidance.
Chemical processing, heat styling and tension
Bleaching, colouring, chemical straightening, heat styling, and tight hairstyles can weaken the hair fibre itself, leading to breakage4.
Inside each strand are millions of hair bonds that give your hair its strength and structure. Repeated chemical and heat damage can break these bonds, making hair more fragile and likely to snap before it reaches its full length4.
Does hair fall mean your hair has stopped growing?
No – hair fall doesn't necessarily mean your hair has stopped growing. Some causes of hair fall can mean a follicle has stopped producing hair, but in many cases, the follicle is still active.
If your hair feels like it is stuck at the same length, it is usually because of one of two things: either your hair is damaged and dry – so it's prone to split ends that travel up the hair shaft – or your hair growth cycle has been disrupted. Either way, the result can feel the same – thin and fragile hair that feels difficult to manage.
How can you support stronger, fuller-looking hair?
When hair feels thin or flat, and you're trying to grow your hair longer and stronger, you need hair care that supports your scalp without weighing fine hair down at the roots.
Our Acidic Grow Full System range is a four-step routine designed for thin, flat hair. Powered by densifying complexes with azelaic acid, it supports scalp care, helps reduce breakage, and creates the appearance of fuller-looking hair.
Below, we explain how to use this range for the best results.
Step 1: Cleanse with Acidic Grow Full System Densifying Shampoo
Start with our Acidic Grow Full System Densifying Shampoo, specifically designed for thin, flat hair that's prone to breakage and hair fall. It’s formulated with azelaic acid to help rebalance your scalp's pH – which is important, because an imbalanced scalp can leave strands feeling weaker and more prone to hair fall. It also includes caffeine and probiotics to awaken and moisturise the scalp, helping create the appearance of density from the root.
Apply directly to your scalp and massage the lightweight shampoo in with your fingertips until it builds into a lather. This helps lift away excess oil, product buildup, and impurities from the scalp while ensuring the formula is distributed evenly. Then rinse.
Step 2: Condition with Acidic Grow Full System Densifying Conditioner
Fine or thinning-feeling hair still needs moisture through the lengths, but heavy conditioners can weigh hair down and leave it looking flatter. That's why our Acidic Grow Full System Densifying Conditioner is formulated to deeply hydrate and moisturise your hair with a lightweight formula that won’t compromise volume. Powered by a 7% Densifying Care Complex with azelaic acid, it instantly helps hair appear thicker and fuller, giving flat lengths a more lifted, bouncy appearance.
After rinsing out your shampoo, apply the conditioner through your mid-lengths and ends, where hair is usually driest and most prone to breakage. Leave on for one to three minutes, then rinse thoroughly.
Step 3: Apply Acidic Grow Full System Scalp & Hair Serum
To build even more volume into your routine, use our Acidic Grow Full System Scalp & Hair Serum – a leave-in serum you can apply to damp hair straight after washing, or to dry hair any time. Formulated with our 5% azelaic acid complex, it offers lightweight support to the scalp to help promote the appearance of thicker hair and reduce hair breakage in the strands, which is especially helpful when you’re growing out damaged hair and want to protect your lengths as they get longer.
Hold the hair serum about 2cm from your scalp, then massage it in with your fingers to distribute it evenly around the roots. Leave in and style as usual.
Step 4: Finish with Acidic Grow Full System Instant Densifying Spray
Finish your routine with our Acidic Grow Full System Instant Densifying Spray. It uses our 5% densifying complex to deliver an instant, fuller-looking finish – while doubling as a heat protectant up to 230°C. Use just before heat styling, or whenever your hair needs a volume boost.
Hold the spray around 15cm away from your hair and mist through your lengths and ends, distributing the formula evenly without overloading any one section. This gives hair a light, flexible finish, while helping protect the fibre from damage.
When should you seek advice about hair fall?
If your hair fall is sudden, severe, patchy, or ongoing – or it's starting to affect how you feel – it's worth seeking expert advice.
Speak to a GP, dermatologist, or professional stylist, depending on your concern. They can help investigate the underlying hair fall cause and point you towards the right next steps.
Now you know what causes hair fall, next learn more about how to fix damaged hair with our ABC 24/7 Night and Day Serum.
1 https://health.clevelandclinic.org/how-much-hair-loss-is-normal
2 https://pmc.ncbi.nlm.nih.gov/articles/PMC9836136/
3 https://pmc.ncbi.nlm.nih.gov/articles/PMC9917549/
4 https://www.mayoclinic.org/diseases-conditions/hair-loss/symptoms-causes/syc-20372926
5 https://www.hopkinsmedicine.org/health/wellness-and-prevention/postpartum-hair-loss
6 https://www.sciencedirect.com/science/article/pii/S0378512225001860
7 https://pmc.ncbi.nlm.nih.gov/articles/PMC5315033/
8 https://pmc.ncbi.nlm.nih.gov/articles/PMC12530271/