Hair Regrowth Decoded: The Deep Guide to Scalp & Hair Science

Written by our senior scientist Sunbin Song, PhD, and edited for clarity by Bradley Yim, our Head of Formulation. You can read more about them on our Team Page.

To achieve a thicker, fuller head of hair, it is important to rejuvenate the scalp skin and hair follicles as well as to protect and condition the visible hair shafts. The only living, growing part of your hair is inside your scalp skin where the hair follicles reside. Hence, to grow thicker hair at a higher density, a scalp serum or other product targeting the scalp is recommended. That is why we created the Full Follicle haircare line which includes a scalp serum, a scalp stimulating shampoo, and an advanced treatment conditioner (learn more).

The visible hair shafts you can see are not composed of living cells. However, these cells have a protective waterproof coating that can get easily damaged by combing, styling, blow-drying, coloring, and improperly cleansing. Modern shampoos and conditioners aim to prevent the stripping of waterproofing while also repairing damage and re-coating hair with waterproofing.

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Hair Follicle Structure

Most of the hair on our body surface is tiny and virtually colorless (vellus hair). However, the hair in places such as our scalp, eyelashes, and eyebrows is longer, thicker, and highly pigmented (terminal hair). Your genetics determine the color of your hair, as well as whether it is straight, helical or wavy, as well as its length, diameter, density and cross-sectional shape. No matter your starting point, as you age, factors come into play that lead to loss of pigmentation resulting in greying, a loss of hair thickness resulting in thinning, slower hair growth, decreased hair density, and in some cases balding (Buffoli et al. 2014).

These aging-related changes are all taking place inside your scalp skin within the dermal layer where the hair follicle resides. The visible part of hair growing outside of your scalp is called the hair shaft, and is made up of dead hair cells. Inside the skin is where all the living hair growth (and resultant hair thinning and hair loss) occurs.

The hair bulb is the part of the hair follicle which is actively producing growth of the hair shaft. It contains the matrix and dermal papilla cells (DPCs), mucopolysaccharide-rich stroma, nerve fibers and a capillary loop that provides the blood supply. Here, melanocytes produce the melanin pigments which give hair its color. Growth factors are also produced to stimulate hair growth. The new hair cells are born in the lower part of the hair bulb and as they move upwards, they increase in volume and become vertically elongated. Finally they are hyalinized so that the keratin of the hair is stabilized (Ohn et al. 2019, Buffoli et al 2014).

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Hair Follicle Growth Stages

The lower part of the follicle shrinks and regenerates according to the phase of growth the follicle is in. At any given time, your hair follicle can be in one of three stages that represent either a growth phase (anagen), or a period of non-growth (catagen, telogen). Catagen is a period of regression and telogen a period of rest. Some also describe a fourth stage — the period in which the hair sheds and the follicle transitions back to anagen (called exogen or regeneration phase).

Hair follicles have a bulge area where the arrector pili muscle inserts. The duct of the sebaceous gland also empties here. The sebaceous gland secretes oily sebum which is what makes your hair and scalp oily. The upper part of the bulge is the infundibulum and the isthmus region. The lower part is the supra-bulbar area and the hair bulb region. The upper part of the follicle is permanent but the lower part regenerates cyclically based on the growth phase.

Throughout these regions of the hair follicle are two layers called the outer root sheath and the inner root sheath. The inner root sheath holds the hair shaft. On the skin side of the outer root sheath there is also a connective tissue layer consisting of two layers of collagen fibers — called the glassy layer or dermal sheet.

The inner root sheath has three sublayers (Henle's layer, Huxley's layer, and the cuticle layer). The inner root sheath anchors the hair shaft to the follicle and produces keratins and trichohyalins that act like cement between cells. Its rigid casing determines the shape of the hair as it grows, guiding its upward movement and determining whether it is curly or straight.

In the scalp, the anagen (growth) phase typically lasts for 2–8 years with a hair growth rate of approximately 1 cm per month. The anagen phase eventually ends and hair growth stops to enter the catagen (regression) phase. Catagen lasts for several weeks, facilitating transition to the telogen (rest) phase which lasts for 2–4 months.

At any given moment approximately 10–15% of hairs are in the telogen resting phase. At the end of telogen, the hair falls out (exogen phase) and a few weeks later, the follicle re-enters the anagen phase. Most individuals have about 100,000 scalp hairs at any time, with a normal shedding rate of 100–150 telogen hairs per day (Buffoli et al. 2014, Natarelli et al. 2023).

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Changes in Hair with Aging and Other Factors

Now that you understand how the hair follicle is structured and how growth and rest phases determine growth and density, you can understand better how aging can lead to hair thinning, greying, and loss.

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Sex Hormones and Hair

Androgenic Alopecia (Male Pattern Baldness)

Hormonal changes, and in particular changes in sex hormones, lead to age-related changes in hair. In simplistic terms, 'male hormones' help males grow beards but can also lead to loss of hair in the scalp regions. Meanwhile, 'female hormones' promote hair growth on the scalp. Much of these hormones are synthesized by the skin and hair follicles themselves.

The androgens are colloquially known as "male hormones" although they are also found in women at much lower levels. The best known androgen is testosterone, but the most potent is dihydrotestosterone or DHT.

DHT is largely responsible for 'male pattern baldness,' also known as 'androgenic alopecia.' DHT directly affects dermal papillae cells (DPCs) to signal a shortened anagen phase and a prolonged telogen phase. This leads to the production of shorter, thinner hair shafts. DHT also enhances apoptosis of hair cells, and the hair follicle miniaturizes — a process called follicular miniaturization. The hair then converts from a terminal hair into a vellus hair (Deng et al. 2022, Ohn et al. 2019, Bansal et al. 2012).

With male pattern baldness, there is a genetically determined increased production of DHT in the frontal scalp. Specifically, the enzyme 5α-Reductase which converts testosterone into DHT is increased above normal levels (Liang et al. 2023). Androgens act through a single nuclear receptor, the androgen receptor (AR), which is present in follicular keratinocytes and dermal papilla cells where a large proportion of receptors are located (Price 1975, Deng et al. 2022).

The majority of testosterone in men is secreted by the testes and testosterone levels in men decrease with age — which might seem counterintuitive, since hair thinning increases with age. This is because testosterone availability is not necessarily the rate-limiting factor. The adrenal glands also secrete androgens including DHEA-S (which has by far the highest serum concentration in both sexes). These weaker androgens are converted into testosterone and DHT by enzymes in the sebaceous glands, epidermal keratinocytes, sweat glands, and hair follicles (Zouboulis 2007).

Second, the impact of DHT on hair follicles combines with other aging factors including senescence, inflammation, and oxidative stress — all detailed below. It is this combination of factors that drives hair loss (Deng et al. 2022).

Men and women show different patterns of androgenic alopecia. Men typically experience bitemporal recession of the frontal hair line followed by diffuse thinning of the vertex. Women have diffuse apical hair loss with a much milder presentation (Villani et al. 2022).

Estrogens, Pregnancy and Menopause

In contrast to androgens, estrogen leads to increased lushness in hair growth. Estrogen receptors are found in hair follicles and notably the hairs on your scalp. This is why there is increased lushness in your mane during pregnancy — estrogen increases the number of hairs in the anagen growth phase. Postpartum, this hair sheds as estrogen levels drop.

Women have higher expression of aromatase enzymes in the scalp hair follicles, meaning more estrogens are produced there. This can protect women from balding and encourage hair lushness. The two principal types of ovarian estrogens are estradiol and estrone — estradiol is seven to ten times more potent than estrone (Cui et al. 2013).

After menopause, estradiol (the primary form of estrogen during reproductive years) drops to near zero. This drop leads to many symptoms of perimenopause and menopause, including thinning hair as hair follicles lose this major estrogen input. Estrogen is also important for the integrity of the skin around the hair follicles, and so post-menopausal loss of collagen, elastin, GAGs, and vascularization of the dermis may also contribute indirectly to thinning hair.

Post-menopause, additional estrogens are produced by peripheral organs including fat tissue, liver, heart, brain, and of course, the skin. The skin's aromatase enzyme can convert circulating androgens into estrogens, so post-menopause the level of estrogens in your body does not drop to zero and can still support hair growth (Cui 2013).

Ultimately, the combination of (1) loss of estrogens with perimenopause and menopause, (2) the relative levels of circulating androgens and estrogens and the enzymes that convert them into their more potent forms, and (3) the levels of receptors as determined by genetics can have a large impact on hair thinning in women. Around menopause, women experience a decline in hair thickness, sebum production, and hair luster from an increase in hair fiber curvature (Villani et al. 2022).

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Senescence

As you age, all the cells in your body undergo a process called "senescence" — a gradual deterioration in a cell's ability to function, divide, and grow. This may be due to telomere damage, accumulated DNA damage, mitochondrial dysfunction, growth arrest, and secretion of proinflammatory factors (Deng et al. 2022).

There is a general decline in growth factors and hair follicle stem cell (HFSC) activity with aging that decreases the ability of the hair follicle to regenerate. In vitro, aged HFSCs show decreased activity even when isolated compared to young HFSCs (Jang et al. 2023). This can be explained in part by altered responsiveness to cell signals that should lead HFSCs to enter a growth stage (Deng et al. 2022).

In senescent cells, there is a decrease in mitochondrial efficiency which leads to greater production of free radicals. Simultaneously there is a drop in activity of free radical-scavenging enzymes, increasing oxidative stress. Melanocyte stem cells (MeSCs) that make pigment also decline — their number decreases rapidly with aging until entirely depleted, likely related to oxidative stress (Jang et al. 2023).

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Chronic Inflammation

With aging there is an increase in levels of inflammatory cytokines around the hair follicles. Age-dependent chronically elevated levels of inflammatory cytokines in the epidermal layer of aged skin inhibit HFSC function. Animal studies show that reversing inflammation can lead to some hair regrowth in aged mice (Jang et al. 2023).

Inflammation can also impair melanocytes contributing to hair graying. Other factors such as obesity, psychological stress, or diseases such as progeria can also drive chronic inflammation around the hair follicle to drive hair thinning, loss and graying (Liang et al. 2023).

Bacteria, fungi and mites live in the scalp feeding off sebum and contribute to conditions like dandruff. As you age, you are worse at fending off microbes. Demodex mite infestation can increase with aging and contribute to inflammation leading to hair thinning (Liang et al. 2023).

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Oxidative Stress

There is increased oxidative stress in the hair follicle with aging. As the ability to clear reactive oxygen species (ROS) declines, this buildup leads to hair graying. Studies show a buildup of ROS such as hydrogen peroxide in up to millimolar concentrations in white hair shafts, with almost absent expression of enzymes that repair oxidized protein residues. Without these repair enzymes, there is a loss of tyrosinase enzyme function in melanocytes and a decline in melanocyte number, leading to loss of pigment (Trueb 2009).

Genetic factors are heavily involved — Asian and African people have later onset and less grey hair than Caucasians. Environmental factors that drive oxidative stress include UV rays, pollution, smoking, nutritional deficiency, emotional factors, and inflammation (Kumar et al. 2018, Villani et al. 2022). For example, studies show smokers are at increased risk of earlier hair graying than nonsmokers (Villani et al. 2022).

Oxidative stress also affects hair quality, linked to decreased keratin-associated proteins and lipid peroxidation in the hair shaft. This leads to hair that is less shiny and more brittle (Liang et al. 2023).

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Reduced Blood Flow Through Dermis with Age

Dermal microcirculation is essential for hair maintenance. It is important for delivery of growth factors, nutrients, cytokines, other bioactive molecules, and for removing waste metabolic products. During anagen, there is high metabolic activity of hair follicle matrix cells and an insufficient blood supply leads to hair follicle diseases. Vascular endothelial growth factor (VEGF) regulates angiogenesis and hair follicle size (Bassino et al. 2020).

Blood flow to the dermis decreases with age. Cigarette smoking also causes changes in the microvasculature of the dermal hair papilla, with negative consequences for hair including thinning and greying (Trueb 2009).

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Hair Follicle and Skin ECM Changes with Aging

Hair follicle and skin aging is associated with a loss of extracellular matrix (ECM) integrity. ECM loss can contribute to premature shedding and also leads to elevated stiffness in the basement membrane which deactivates HFSCs (Jang et al. 2023).

We lose many structural proteins in the ECM with aging — including collagen, elastin, and hydration-boosting glycosaminoglycans. Photoaging accelerates this process and leads to elastosis, where degraded elastin molecules accumulate. Solar elastosis can precede hair thinning and decreases in hair diameter. Bald regions of the scalp often show signs of solar elastosis, suggesting UV skin damage can accelerate balding in those with androgenic alopecia (Trueb 2009).

Autoimmune, Drug-Induced, and Other Causes

Autoimmune disorders such as Alopecia Areata (AA) can also lead to hair loss and usually strike during the early adult phase of life. Lifetime prevalence is 1.7% in both men and women (Rinaldi et al. 2019).

Frontal Fibrosing Alopecia is a scarring alopecia that involves the frontotemporal hairline and eyebrows. It is often found in postmenopausal females with mean onset of 60 years old. Immune cells gather around outer root sheaths and there is scarring around the hair follicles (Villani et al. 2022).

Many drugs can also induce hair loss. In drug-induced telogen effluvium, hair loss is evident 2–4 months after starting treatment and is temporary, disappearing with drug discontinuation (Villani et al. 2022). Hypo- and hyperthyroidism can also cause telogen effluvium and reversible diffuse hair loss. Dietary deficiencies in essential amino acids histidine, leucine, and valine and non-essential amino acids alanine and cysteine can also lead to hair loss (Natarelli et al. 2023). Chemotherapy can lead to hair loss; scalp cooling is a technique which decreases the delivery of cancer-fighting drugs to the scalp, mitigating chemotherapy-induced hair loss (Natarelli et al. 2023).

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FDA-Approved Treatments for Hair Loss

A. Drug Treatments for Androgenic Alopecia

For androgenic alopecia, topical minoxidil (for men and women) and oral finasteride (Propecia) (for men only) are the only FDA-approved prescription medications.

Minoxidil relaxes blood vessels and increases blood flow to increase hair follicle size. Additionally, it is an anti-inflammatory and an anti-androgen. However, there can be contact dermatitis including skin itching (Ohn et al. 2019, Natarelli 2023). For males, a topical 2–5% solution or 5% foam used twice daily can improve or prevent the progression of androgenic alopecia. For women, a 2% solution or 5% foam once daily is recommended. About 60% of males respond to topical minoxidil treatment (Liang et al. 2023).

Finasteride inhibits 5-alpha reductase, the enzyme that converts testosterone into DHT. Studies show 99% of men with male pattern baldness respond positively to finasteride (Natarelli et al. 2023). However, continuous use is necessary as hair regrowth will be reversed when treatment is stopped (Liang et al. 2023). Dutasteride is another 5-alpha reductase inhibitor prescribed off-label.

B. Drug Treatments for Androgenic Disorder–Related Alopecia

For women, androgenetic alopecia along with hirsutism (beard) and acne may actually be due to an androgenic disorder. 90% of cases are due to polycystic ovary syndrome. This condition may be treated with estrogen and progestin combination pills, which enhance gonadotropin suppression of ovarian androgen secretion. Cyproterone acetate and spironolactone can also be given as anti-androgens in this population (Zouboulis 2007).

C. Light Therapy for Alopecia

Light therapy — also known as photobiomodulation therapy (PBMT) or low level laser therapy (LLLT) — is an FDA-approved treatment for hair loss. Devices do not require a prescription and several have shown efficacy. Red light can penetrate the scalp and be absorbed by enzymes in the mitochondria of hair follicles so that they function better, increasing growth factors and blood flow and prolonging the anagen growth phase.

D. Hair Transplantation

Hair transplantation therapy can also be employed to help treat bald areas. However, since these hair follicles are still subject to the aged skin environment and hormonal factors, they remain subject to some of the same factors that led to hair loss in the first place (Jang et al. 2023).

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Non-Prescription Topical Scalp Actives That Can Improve Hair Thickness and Density

Many topicals are not FDA approved but have shown efficacy in studies. These include anti-fungals such as ketoconazole (a cortisol inhibitor that can help increase hair density) and prostaglandins such as bimatoprost and latanoprost which are popular in eyelash growth serums (Natarelli et al. 2023). Here we go over the evidence supporting modern topicals that use actives such as peptides, growth factors, caffeine, vitamins, and botanicals. Where relevant, we detail the actives found in our Full Follicle line (learn more).

A. Peptides (Acetyl Tetrapeptide-3)

Acetyl tetrapeptide-3 can be found in lash, brow, and hair growth serums. In the Full Follicle line, it is just one of 14 actives.

Acetyl tetrapeptide-3 stimulates dermal papilla cells to increase hydroxyproline, collagen type 3 and laminin production for better ECM integrity and better hair anchoring to reduce shedding, as well as increased hair follicle size. Treatment has been shown to stimulate hair growth and increase hair length compared to no treatment.

In a clinical study of 32 patients with mild to moderate androgenic alopecia, acetyl tetrapeptide-3 combined with ginseng extracts and biochanin A demonstrated comparable efficacy at 24 weeks to 3% minoxidil in increasing terminal hair counts (8.3% compared to 8.7%) (Lueangaran and Panchaprateep 2020).

In another industry-sponsored clinical study, acetyl tetrapeptide-3 in combination with red clover extract was found to boost the percent of hair follicles in anagen by 15% and decrease hair follicles in telogen by 52% compared to placebo after 4 months of daily application in lotion form — boosting hair density. It was found to have similar benefits in rinse-off form as well (Capixyl).

B. Growth Factors and Platelet Rich Plasma (PRP)

The Full Follicle line uses a growth factor complex of five growth factors (EGF, aFGF, IGF-1, VEGF, bFGF) derived from vegan lab-derived sources.

A diverse array of growth factors regulate the stages of hair growth. Growth factors such as epidermal growth factor (EGF) have been found to operate like a biological switch that turns on hair follicle growth to mark the beginning of anagen (Mak and Chan 2002). Deficiency of insulin-like growth factor 1 (IGF-1) is implicated in androgenic alopecia — balding scalp follicles secrete significantly less IGF-1 than non-balding scalp follicles (Trueb 2018).

Due to synergies between growth factors, a combination of growth factors rather than a singular one is more effective (Krane et al. 1991).

Platelet rich plasma (PRP) is one popular route by which these growth factors have been delivered to hair follicles. PRP is naturally rich in platelets and several growth factors found in plasma. Clinical studies have shown increased hair density and diameter in men, and an increase of hair diameter in women (Natarelli et al. 2023).

However, PRP therapy is costly and time consuming as well as being human sourced. For this reason, topical serums containing synthesized growth factors have been developed. Industry-sponsored clinical studies using a topical mixture of 5 different synthesized growth factors (sh-Polypeptide-1/IGF-1, sh-oligopeptide-2/bFGF, sh-Polypeptide-9/VEGF, sh-Oligopeptide-10/EGF, sh-Polypeptide-11/aFGF) demonstrated decreasing scalp sensitivity and increasing hair thickness after 4 weeks of regular use, with even greater benefit after 30 weeks (Bio-placenta Hair).

C. Caffeine

Caffeine counteracts DHT-induced miniaturization of the hair follicles and is included in our Full Follicle line. Caffeine inhibits phosphodiesterase and increases cAMP levels promoting cell proliferation — the mechanism by which it counteracts DHT-induced follicular miniaturization. In one in-vitro study using scalp hair follicle biopsies from male subjects, caffeine stimulated hair follicle growth and counteracted the negative effects of testosterone on the hair follicle (Fischer et al. 2007).

Clinical studies show caffeine can penetrate into hair follicles after topical application. Topical caffeine was found to be more effective than 5% minoxidil in men with androgenic alopecia, and in women, a shampoo with caffeine was found to significantly reduce hair loss (Bansal et al. 2012, Bassino et al. 2020).

D. Vitamins

Vitamins are crucial to healthy skin and hair. The Full Follicle line contains panthenol (Vitamin B5) and biotin (Vitamin B7).

Deficiencies in B vitamins including B2 (riboflavin), B7 (biotin), B9 (folate), and B12 have been associated with hair loss. However, dietary deficiencies in these vitamins are extremely rare in the US and supplementation usually does not improve thinning hair. The exception is biotin, which can occur in pregnant women — some studies find up to 50% of pregnant women deficient in biotin (Almohanna et al. 2019).

Vitamin B5 (panthenol) deficiency is not associated with hair loss, but studies show benefits of panthenol supplementation for aging-related hair thinning. One study showed it helps the survival of hair dermal papilla cells and outer root sheath cells. Panthenol reduced markers for apoptosis (cell death) and senescence (aging) in aged and telogen hair follicles, and triggered or elongated the anagen phase by stimulating anagen-inducing factors, B-catenin and versican, and increased VEGF growth factor expression (Shin et al. 2021).

Panthenol is also common in hair products because it can both coat the hair shaft forming a protective film and penetrate the hair shaft where it strengthens hair. Other vitamins and minerals whose deficiency is linked to hair loss include Vitamin D and Iron (with Vitamin C), and oral dietary supplementation is recommended in those cohorts (Almohanna et al. 2019).

E. Botanicals and Phytocompounds

The Full Follicle line contains Swiss apple stem cells, Red Clover, Rosemary, Ginseng and Eucalyptus, along with Green Tea, Grapeseed and Aloe.

F. Ketoconazole

Ketoconazole is an ingredient in medicated anti-fungal shampoos. It is also a cortisol inhibitor and partly through this inhibition, it can help increase hair density. Studies suggest that continual ketoconazole application is required to maintain hair regrowth (Natarelli et al. 2023).

G. Prostaglandins

Prostaglandins such as bimatoprost and latanoprost can promote eyelash hair growth and are popular in eyelash growth serums. They have also been applied to the scalp with positive results for hair density and hair growth (Natarelli et al. 2023), though they can cause darkening of eyes and skin around the eyes.

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Taking Care of the Hair Shaft with Proper Washing and Conditioning

Though all the good stuff that will lead to thicker, denser, fuller hair happens in the living part within the scalp skin, a beautiful head of hair also requires maintenance care of the visible hair shaft.

Harsh cleansers as well as styling, coloring, perming, and blow-drying will damage your hair — removing the waterproofing coating and leaving it brittle. Without proper conditioning, hair is difficult to comb and rough combing will also damage the cuticle. Proper cleansing and conditioning should leave hair looking sleek and shiny and easy to comb.

Hair Shaft Structure and Sources of Damage

The visible hair shaft has three concentric layers: the medulla on the inside, then the cortex, and finally the cuticle on the surface.

The cuticle is a very resistant layer that consists of overlapping cells arranged like shingles on a roof. This is the hair's protective barrier. The cuticle has sublayers: the endocuticle, the exocuticle, and the outer epicuticle. The epicuticle is the waterproof hydrophobic lipid layer made of 18-methyleicosanoic acid (18-MEA) that is bonded to the fiber — it is anchored firmly in place and does not easily wash off (Gubitosa et al. 2019).

Nonetheless, repeated washing with harsh shampoos will start to remove these lipids from the epicuticle and slowly the hair loses its waterproof quality, then swells from water absorption when wet — damaging the inner parts of the hair. Chemical procedures like perms or coloring will also damage the cuticle. Rough brushing and combing causes further cuticle damage.

Why Proper Scalp Cleansing Matters

The hair follicles contain glands that produce sebum, a waxy lipid substance that deposits on the skin and hair surface. The scalp is also dark due to the hair covering it. Hence, the scalp is a dark, moist and sebum-rich environment — ideal growing conditions for microbes like Malassezia, a type of yeast. Without cleansing, your scalp becomes infested with these microbes which play a role in dandruff and seborrheic dermatitis. Folliculitis can also result. Malassezia also oxidizes sebum and these oxidized lipids are irritating to skin. All this will harm hair growth.

Studies looking at extreme low wash-frequency conditions in an Antarctic research team and in International Space Station astronauts found increases in scalp itch and flakes and a dramatic rise in scalp Malassezia levels. Less extreme studies also find lower wash-frequency associated with increased prevalence of dandruff and seborrheic dermatitis (Punyani et al. 2021).

One study by Punyani and colleagues of 1500 men and women found that scalp flaking, dandruff, itch, and dryness were much lower for those who washed at least 5–6 times a week. Compared to a period of no washing for seven days, daily washing with a scalp care shampoo produced less oxidized lipids, less flaking, and less odor. Hair itself had less oxidized sebum and was less greasy.

Keep in mind this study only looked at those of Chinese ethnicity who have a specific hair type. The AAD has different advice based on hair type, ethnicity, and how treated your hair is. For those with oily hair, washing once a day may be appropriate. For chemically treated hair, less frequent washing is suggested. For Black hair, the AAD recommends washing just once a week or every other week (AAD).

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Picking the Right Shampoo and Conditioner

When choosing a shampoo, focus should be on the scalp. The right shampoo will thoroughly cleanse your scalp while minimally damaging your hair. Conditioners are mainly meant for the hair — to coat, waterproof, fix damage, and make hair easier to comb.

How Mild Shampoos Differ from Harsh Ones

You should avoid any shampoo that contains soaps as a cleansing agent. Soaps can leave behind soap scum when mixed with hard water, and both the scalp (pH 4.5–6.2) and the hair shaft (pH ~3.67) are naturally acidic and harmed by the alkaline pH of soaps (Cline et al. 2018, Dias et al. 2014).

Shampoos are typically synthetic detergents (syndets). Some syndets are harsher than others — avoid harsher ones like sulfates (SLS and SLES). Milder sulfate-free formulas use syndets like 'isethionates' or 'sulfonates' (Draelos 2010, D'Souza and Rathi 2015).

Anionic surfactants (sulfates and sulfate-free syndets alike) are good at removing sebum and dirt but can leave a negative charge on the hair surface increasing frizz and friction. This is why nonionic or amphoteric surfactants may be added to shampoo formulas — most mild shampoos contain a blend of anionic, nonionic, and amphoteric surfactants (Dias 2015, Draelos 2010, Gubitosa et al. 2019).

Those drawn to "natural" cleansing may be interested in products containing natural saponins from sarsaparilla, soapwort, soap bark, ivy agave, or Indian herbs like soapnut (Reetha), Amla, and Sheekakai. However, herbal saponins alone are generally poor cleansers, and when you find herbal shampoos touting these ingredients, they are typically mixed with the same syndets found in non-herbal shampoos (Dias 2015).

Liquid shampoos contain other additives beneficial to scalp and hair. pH adjustors like citric acid may be added (hair is more damaged by alkaline products). Sequestrant agents remove minerals from hard water that can lead to scalp scum. Medicated shampoos may contain zinc pyrithione, salicylic acid, selenium sulfide, or other anti-dandruff/antifungal actives for conditions like seborrheic dermatitis or psoriasis. Those with thinning hair may also want a thickening shampoo that contains additional actives such as caffeine, peptides, and botanicals (Draelos 2010).

How Conditioners Work to Repair and Protect Hair

No matter how mild the shampoo, washing hair makes hair rough. That is where conditioners come in. The right conditioner can restore hair waterproofing, help repair damage, reduce frictional forces, and minimize static electricity.

Conditioners neutralize the negative charge left by anionic surfactants by adding positive charges (cationic syndets and polymers). Damaged hair also carries a negative charge; cationic molecules in conditioners bind to this negatively charged damaged hair. Neutralizing this charge diminishes static, frizz and friction.

Panthenol (Provitamin B5) is popular in conditioners as it can stick to hair and absorb into the deeper layers where it acts as a humectant. Plant oils and butters contain fatty acids which can also penetrate and coat the hair shaft improving its waterproofing.

Silicones are in the majority of conditioners due to their ability to coat hair strands and make them shiny and frizz-free. However, we believe silicone-free hair products are better for thinning hair or haircare systems with scalp actives. Silicone coatings may build up on hair leading to a heavy, weighed-down look. For those with thin hair, this may lead to hair that is flat and lifeless. For those with damaged hair, the silicone coating can prevent absorption of beneficial ingredients into hair strands and scalp, reducing the ability of hair damage to be fixed from the inside (Dias 2019).

How to Properly Use Shampoo and Conditioner