Why hair thins, and what the science says about preventing hair loss

How hair grows, and why some shedding is normal

Every hair on your head grows from its own follicle, and each follicle works through a repeating cycle. At any given time, most of your hair is in the growth phase, while a smaller share is resting or shedding.⁴

Losing 50 to 100 hairs a day is normal, and you will notice more on the days you wash or brush.¹ The hairs that come out were already in the resting phase and would have shed anyway. Thinning becomes visible when that balance shifts: when more follicles drop into rest at once, when the growth phase gets shorter, or when follicles gradually shrink and produce finer hair.

Why hair thins: the most common causes

Thinning rarely has a single cause. Many people have two or more of the ones below.

1. Genetics and hormones (pattern hair loss)

Pattern hair loss, known medically as androgenetic alopecia, is the most common cause of thinning in both men and women.²³ In people who are genetically susceptible, the hormone dihydrotestosterone (DHT), made from testosterone by an enzyme called 5-alpha-reductase, gradually shortens the growth phase. Over many cycles, affected follicles shrink and produce shorter, finer hairs, a process called miniaturization.²

In men, it usually shows as a receding hairline or thinning at the crown. In women, it more often appears as a widening part and diffuse thinning over the top of the head, with the front hairline intact.³

2. Hormonal shifts in women

The drop in estrogen around perimenopause and menopause can make the effects of androgens on the follicle more noticeable.³ Many women also experience heavy shedding two to four months after giving birth, which typically settles on its own.⁴ Thyroid conditions and polycystic ovary syndrome (PCOS) are other common hormonal contributors, and both are worth ruling out with a doctor.

3. Stress, illness and major life events

A significant shock to the body, such as a high fever, surgery, severe illness, major emotional stress or a sudden change in diet, can push a large number of follicles into the resting phase at the same time. This is called telogen effluvium. Because the resting phase lasts around three months, the shedding usually starts two to three months after the event, which is why people often don’t connect the two.⁴

Telogen effluvium is usually temporary, and hair tends to recover within about six months once the trigger has passed.⁴ Research in mice has also shown how the stress hormone corticosterone can keep hair follicle stem cells in an extended resting state, which may be one reason long-term stress affects hair.¹⁰

4. Nutrition

Hair follicles are some of the most active cells in the body, so they are sensitive to shortfalls. Low iron, low vitamin D, low zinc, too little protein and rapid weight loss have all been linked to shedding.⁵ If you are not deficient, there is little evidence that extra supplements help, and too much vitamin A or selenium can cause hair loss.⁵ A blood test will show whether you are low in anything.

5. Styling habits and tension

Tight ponytails, braids, buns, extensions and weaves pull on the follicle over and over. Over time this can cause traction alopecia, usually along the hairline and temples. Caught early, it is reversible. If the tension continues for years, the damage can become permanent.¹¹

6. Scalp health

Researchers have linked oxidative stress, inflammation and long-running scalp problems such as flaking to poorer hair quality and more shedding.¹² Keeping the scalp clean and free of buildup makes sense as part of regular hair care.

7. Age

As we get older, the growth phase naturally shortens and individual hairs tend to become finer, so some reduction in volume is a normal part of ageing for everyone.²

Warning signs that deserve a doctor’s visit

Gradual thinning is rarely urgent. Some patterns should still be checked by your family doctor or a dermatologist. In Canada, your family doctor can order blood work and refer you to a dermatologist if needed. Book an appointment if you notice:

Preventing hair loss: what helps

Genes set your risk of pattern hair loss, and there is a lot you can do around them. For temporary shedding, dealing with the trigger usually lets hair recover. For pattern hair loss, starting early tends to keep more hair, because it is easier to keep existing follicles active than to revive ones that have already shrunk.⁶

Start with the cause

The most useful step in preventing hair loss is a diagnosis. A doctor can check for iron deficiency, thyroid problems and hormonal conditions, and tell pattern hair loss apart from temporary shedding.

Know the treatments with the strongest evidence

For pattern hair loss, European evidence-based guidelines recommend topical minoxidil for both men and women, and oral finasteride for men.⁶ In Canada, minoxidil is sold without a prescription, while finasteride requires one. Both work best when started early and must be used continuously to maintain results. Your doctor or pharmacist can explain the benefits and side effects for your situation.

Eat for your hair

A balanced diet with enough protein, iron-rich foods and a variety of fruit and vegetables supports healthy hair growth. If you suspect a deficiency, get tested before taking supplements.⁵

Go easy on styling

Loosen tight hairstyles, change your part and ponytail position regularly, give extensions a break, and limit high heat and harsh chemical treatments.¹¹

Manage stress and sleep

Major stress can trigger shedding months later, so sleep, exercise and managing stress count as hair care too.⁴¹⁰

Look after your scalp

Keep your scalp clean and comfortable, and take a few minutes to massage it. In one small study, nine men who had a four-minute standardized scalp massage every day for 24 weeks showed an increase in hair thickness, although the number of hairs did not change.¹³

Botanicals for hair: what the research says

Plant extracts have a long history in hair care, and researchers have studied several of them in human trials, animal studies and lab tests. Below is what they found for the botanicals people ask us about most. All of them are in our Hair Therapy formulas.

Rosemary

Research: a six-month human trial, plus lab and mouse research

In 2015, researchers randomly assigned 100 men with pattern hair loss to apply either rosemary oil or 2% minoxidil to the scalp twice a day for six months. Hair counts rose significantly in both groups at six months, with no significant difference between them.⁷ In mice, rosemary leaf extract has also been shown to block 5-alpha-reductase and promote regrowth.¹⁴ Our full guide to rosemary oil for hair covers the research in detail.

Saw palmetto

Research: human trials, mostly with oral supplements

Saw palmetto, from the berries of the Serenoa repens palm, is known for inhibiting 5-alpha-reductase, the same enzyme that finasteride targets. In a two-year study of 100 men with pattern hair loss, 38% of those taking 320 mg of saw palmetto daily improved, and 68% of those taking finasteride improved.⁸ An earlier trial of an oral saw palmetto and beta-sitosterol combination reported improvement in most participants.¹⁵ A 2020 systematic review found positive results across several studies of oral and topical products.¹⁶

G Ginseng

Research: cultured human hair follicles and mice

In a 2015 study, red ginseng extract and its active compounds, called ginsenosides, increased the activity of cultured human hair follicle cells and counteracted some of the effects of DHT in the lab. The extract also sped up hair growth in mice.⁹

Amla

Research: human follicle cells in the lab

Amla, or Indian gooseberry (Phyllanthus emblica), has a long history in Ayurvedic hair care and is rich in antioxidants. In the lab, amla fruit extract increased the growth of dermal papilla cells, the cells at the base of the follicle that help regulate the hair cycle.¹⁷

H Hibiscus

Research: animal and lab studies on a related species

Leaf and flower extracts of Hibiscus rosa-sinensis promoted hair growth in animal and lab testing.¹⁸ HUSSSH uses bark extract from a different species, Hibiscus syriacus, which was not part of that research.

C Cedarwood

Research: a human trial of a four-oil blend

In a 1998 trial, people with alopecia areata, an autoimmune form of hair loss, massaged a blend of thyme, rosemary, lavender and cedarwood essential oils into their scalp every night for seven months. 44% of that group improved, compared with 15% of those using carrier oils alone.¹⁹ Cedarwood was one of the four oils, and the study used Atlas cedarwood. HUSSSH contains Himalayan cedarwood (Cedrus deodara).

Argan oil

Research: antioxidant and conditioning research

Argan oil is rich in vitamin E and fatty acids, and research has focused on its antioxidant and nourishing properties.²⁰ In hair care it is valued for conditioning, softness and shine.

A scalp-first daily routine

Whatever the cause of your thinning, these habits are worth building.

1. Cleanse regularly and gently. Washing does not cause hair loss. If your scalp feels tight or dry, a milder sulphate-free cleanser may feel more comfortable.
2. Massage while you wash. Use your fingertips, not your nails, and take a few minutes over it.¹³
3. Condition the lengths. Conditioner reduces breakage from brushing and styling, which helps hair look fuller.
4. Style with less tension and heat. Rotate hairstyles and let your hair air-dry when you can.¹¹
5. Support it from the inside. Eat well, sleep well, and get blood work if you suspect a deficiency.⁵
6. Give it time. Hair grows about a centimetre a month, so any change takes months to show.

Frequently asked questions about preventing hair loss