Trichology News

Understanding Hair

Hair Shaft

General description of hair as a skin appendage By Marta Teixeira

This article will look at the general description of hair as a skin appendage, its normal growth phase, resting phase and shedding phase. It will also be approached the psycho social impact and psycho-social influences that hair loss patients have throughout their lives. Dermatology nurses should also be aware of the main hair loss and scalp conditions, so handy hints on what to do and what not to do to keep hair and scalp healthy will be mentioned in this article.

 

Introduction

There are a range of significant symptoms related to hair and scalp disorders that can lead to a change in the physical appearance and psychological distress in patients. The NHS (National Health Service) should provide these patients with a dermatological examination (including using a trichoscope on the consultation), arrange any necessary investigations to achieve a diagnosis (such as blood tests or a scalp biopsy) and advise patients on the appropriate treatment. This is a range of dermatology that is not as approached on the NHS, meaning that most patients will see themselves in the need to go to a hair loss specialist privately. Hair loss consultations are not a regulated area, meaning that anyone can call themselves a hair loss specialist or Trichologist. Many General Practitioners (GP) are not referring hair loss patients to a dermatologist and most hair loss treatments are also not available on the NHS (1). This article will provide an overview of the science of hair and hair care to dermatology nurses.

 

Structure of hair

Hair is only found in mammals, meaning that the growth cycle of hair follicles is synchronized regionally so that waves of hair loss and replacement go through the entire body. In the human body, each individual hair follicle has its own independent cycle. (2)

Although hair nowadays is seen as an inherited look, it also has very important roles, such as protecting the scalp from the UV light, protect the scalp from trauma, influence body temperature and have sensory functions. (3)

Each hair is made up by two separate structures: the hair shaft, which is the visible part outside the skin and the follicle, which is located underneath the surface of the skin. (3)

All hairs are keratised non-living structures and are formed in the hair follicle, a living follicle that enlarges at the base and forms the hair bulb, which is distributed all over the entire surface of the skin, except on the palms and soles. (4)

Each hair shaft is composed of a cortex, surrounding cuticle cells and a medulla that is only found on thicker hairs. It is this feature that plays an important role in determining the physical and mechanical properties of the hair, such as strength, texture and colour. (4)

Hair Shaft

(6)

The follicle is located underneath the surface of the skin and makes the hair grow. This structure is composed of the inner root sheath and the outer root sheath. (4)

The outer root sheath is the place where the stem cells are located and are responsible for differentiating cells such as melanocytes and keratinocytes. Most authors defend that these stem cells are located within the bulge area, between the arrector pili muscle and the ductal opening of the sebaceous gland. (4)

The inner root sheath consists of the Henle layer, the Huxley layer and the cuticle layer that helps to fix the hair that is growing onto the hair follicle. The cuticle is the most known hair shaft structure for cosmetic reasons, since it’s the main feature that if not cared for, it will show an odd appearance on the hair. Cuticles are like shingles on a roof, overlapping cells that protect the hair shaft from its hair follicle. (4)

 

Hair StructureThe hair bulb is the bottom region with a small mass of cells that produces hair. This structure extends into the dermal layer of the skin and surrounds the dermal papilla. The papilla is composed of connective tissue and is associated with nerve fibers and a loop of the capillaries that supplies nutrients. This is the main region important for the hair growth process, that will determine characteristics like size and colour of the hair shaft. The dermal papilla lies beneath the hair follicle, which makes it the main communication link between the hair follicle, the hair, and the rest of the body. This consists of a complex mix of growth factors, stem cell factors, keratinocyte growth factor and bone morphogenetic protein. (4)

The arrector pili muscle is controlled by the autonomic nervous system which makes the hair shaft elevate and trap air to maintain the body heat in cold conditions. The dermal papilla is trapped by small arterioles that originate from the subcutaneous fat. These capillaries nourish the hair follicle by delivering oxygen and nutrients. Just like the skin, hair is created from rapid division and differentiation of stem cells that turn into the keratinized cells. The hair shaft that grows on the surface of the skin is just composed of keratin. (4)

 

Types of hair

There are 3 types of hair based on their characteristics: terminal, vellus and lanugo. Hair that is darker, visible to the human eye, coarse, thick hair that is found on the scalp, underarms and pubic area is called terminal hair. In men, terminal hair is also found on the face and chest and this type of hair on these areas are related to androgen-dependent sites under the influence of testosterone. Areas of the body that look hairless, but with a closer look it can be seen shorter, finer, lightly pigmented that lack the medulla layer and are mainly found on the face, arms and stomach are called vellus hair. Lanugo hair is the type of name given for the fine, non-pigmented hair that lacks the medulla layer and covers the fetus. These hairs usually have some centimeters long and by the first weeks of life, lanugo hair is replaced by vellus hair on the body and by terminal hair on the scalp. (8)

The only parts of the external surface of the body that don’t have any hairs are the palms and soles of the hands and feet, lips, labia minora and glans penis.

 

Purpose of hair

Different evolutionary theories claim that humans were able to maintain the hair on the scalp because the head is directly exposed to the sun and to retain heat at night, since the brain is very metabolically active and is able to produce heat, and hair on the scalp is able to maintain warmth. (9)

As a physical blocker, hair does help shield the scalp from some of the sun’s ultraviolet (UV) rays. Studies show that hair provides a barrier against both UVB and UVA radiation which is significantly increased with respect to the hair density, thickness and the presence of melanin. When a person is standing, the scalp is perpendicular to the sun’s rays and therefore receives high doses of radiation, explaining the relatively high incidence of skin cancers in this area. (10)

Some authors mention that this also plays a big role on sexual selection. It was found that modern indigenous people with no contact with nowadays society style their hair, suggesting that ancestors should do this as well. (9)

Abrasions are not that common on the scalp because of the presence of thick hair, which tends to prevent or blur the patterned effect of blunt force injuries. It can be difficult to detect a bruise on the scalp because of hair. (11)

We must remember as well that the hairy skin of mammals represents one of the largest sensory surfaces, responsible for the ability to sense angular acceleration of the head (rotational movements), linear acceleration (translational movements), and postural orientation with respect to gravity. (12)

In human beings, specialized hairs such as eye lashes and hairs inside the nostrils and external ears afford some protection from the environment. Eyebrows prevent sweat from getting into the eyes. On the inner ears of human cadavers, sound entering the cochlea generates traveling waves along the length of the basilar membrane. Scalp hairs may assist in stabilizing the temperature of the brain. Hairs can also excrete toxic substances like arsenic, and are thus of use in forensic medicines. The hair follicle is an important model system for studying basic biological problems. Repigmentation in vitiligo patches often starts around hair follicles. So, even though hairs have no longer survival value, they do serve useful functions and are not completely vestigial. (13)

 

Variations in terminal hair colour

Colour contributes to the overall visual appearance of hair. Follicular pigmentation is responsive for numerous factors such as: hair cycle-dependent changes, body distribution, racial and gender differences, variable hormone responsiveness, genetic defects and age-associated change. The hair bulb is the only site of pigment production for the hair shaft and melanocytes are distributed just below the pre-cortical keratinocytes, from where melanin can be transferred to the hair shaft cortex. Melanocytes are located beyond the reach of direct stimulation by UV radiation – the principle regulator of melanocytes in the epidermis. (14)

Melanosome structure correlates with the main type of melanin produced:

Dark brown/black hair bulb melanocytes contain the largest number of melanosomes with a highly ordered fibrillar matrix. These melanosomes are termed true or eu-melanosomes and their melanin termed true or eu-melanin. (14)

Brown hair bulb melanocytes also contain eumelanosomes, but these are smaller than in black hair. (14)

Blond hair follicle bulbs produce weak melanized melanosomes, with so little eumelanin that their melanosomal matrix is visible as is not hidden by melanin.

Red hair bulb melanocytes produce the pheo-melanosome,  with a disordered internal structure. Unlike the fibrillar core of the eumelanosome, the pheomelanosome contains a vesicular matrix with red/yellow melanin deposited irregularly in a random fashion. Eumelanogenic and pheomelanogenic melanosomes often co-exist in the same normal human melanocytes. (14)

Hair colour also shows striking age-related changes, such as that hair colour in children usually darkens with advancing age. (14)

Scalp hair bulb melanocytes are at their most active during youth, when the follicular melanin unit is just a few hair growth cycles old and also when they are most responsive to the full post-puberty hormonal stimulus. There is experimental evidence to suggest that the melanocyte stem cell reservoir in adult hair follicles may be rather limited. (14)

The onset and progression of hair greying correlates closely with chronological ageing and occurs to varying degrees in all individuals, regardless of gender or race, being genetically controlled and inheritable. Scalp hair greying first appears usually at the temples, and spreads to the vertex and then the remainder of the scalp affecting the occiput last. Beard and body hair is usually affected later. Greying happens because of a marked reduction in melanogenically active melanocytes in the hair bulb of anagen hair follicles. (14)

 

Texture and shape

Hair fibres show a wide diversity across and within all human populations, although they typically have the same basic structure, the three-dimensional shape of the entire fibre varies considerably depending on ethnicity and geography, going from very straight hair with no rotational turn about the long axis, to the tightly sprung coils of hair. (15)

Genetic factors seem to play a major role in determining hair texture—straight, wavy, or curly—and the thickness of individual strands of hair. Studies suggest that different genes influence hair texture and thickness in people of different ethnic backgrounds. (15)

The dominating ancient hominid scalp hair form was curly because of the ability of the curved shape to raise the fibre root away from the skin, thereby delivering both UV protection and scalp cooling. With migration from the hot climate into colder areas, evolutionary adaptation is thought to have caused changes in hair shape and colour. (16)

Some authors mention that changes throughout life in the intrinsic hair form may be related to a health condition or drug effect. Woolly hair may point to certain autosomal recessive hair disorders, and changes in hair shape have been observed from treatment of certain conditions, such as chemotherapy, the so called “chemo curls”. (16)

Early studies on follicle morphology described a direct correlation between follicle shape and race. It has also been demonstrated that curly fibres, emerging angularly from the scalp, are generated by curved follicles (that have a retrocurvature at the bulb). Straight hair, on the other hand, emerges from collinear follicles that are embedded at approximately right angles with the scalp. Besides having a curved follicle contour, the bulb and other curly fibres also exhibit an asymmetry in shape and cellular distribution, as opposed to symmetry and homogeneous cellular dispersal in straight hair fibres. (16)

Breaking and reformation of disulfide bonds on the hair are processes that are closely associated with changes of fibre curliness (such as straightening hair or chemical treatments) so this means that these bonds are believed to help on hair curvature. (16)

 

Normal Hair growth:  Phases of hair growth

The growth of the hair follicle is cyclical. Stages of rapid growth and elongation of the hair shaft alternate with periods of quiescence and regression driven by apoptotic signals. This cycle can be divided into three phases: anagen (growth), catagen (transition), and telogen (rest). (4)

Anagen growth is the active phase where the hair follicle works to produce the hair fibre, this means that the follicle starts proliferating hair progenitor cells and also begins the process of differentiation. Under normal conditions, 85% of hairs on an adult human scalp are in the anagen phase, and this can last up to 2 to 6 years. Hairs in the eyebrows and eyelashes only need a couple of months to grow. To signal the beginning of the anagen phase, the dermal papilla signals the multipotent epithelial stem cells in the bulge. Once these stem cells are stimulated, the inferior segment of the hair follicle can now grow downwards, forming a bulb around the dermal papilla. Now, the dermal papilla can signal matrix cells in the bulb to proliferate, differentiate, and grow upwards, forming a new hair. (4, 6)

The catagen phase starts when the anagen phase finishes. This phase can last just a few weeks and the hair follicle undergoes apoptosis-driven regression and loses about one-sixth of its standard diameter. Usually about 1% of hairs are in the catagen phase on a normal adult hair scalp. During this phase, cell division in the matrix ceases, and the inferior segment of the hair follicle begins to regress. Eventually, the inferior segment of the follicle no longer exists, and the dermal papilla has moved upwards to contact the bulge once again. During this process, a club hair is formed with a white, hard node on the end. (4, 6)

The last phase is called the Telogen phase, which means that this is the resting phase of the hair cycle. In this phase the hair follicle is dormant and the growth of a new hair shaft doesn’t occur. This phase can last from a few weeks for eyelashes to about 3 to 4 months in scalp hair. About 10% to 15% of all hairs in the body are in this resting phase at any given time and can remain in this state for a variable amount of time, depending on its location. (4)

The bulge activation theory posits that growth factors produced in the dermal papilla stimulate bulge stem cells to proliferate and modulate growth-phase transitions. Because these cells are transient amplifying cells, they only can go through a limited number of mitoses, thereby setting the duration of anagen and onset of catagen phases. (6)

At birth, all hairs begin in the anagen phase; the human scalp contains over 100,000 hairs. At any one point in time, most hairs (85% to 95%) are commonly found in the anagen phase and these hairs can grow approximately 1 cm per month. Meanwhile, hair loss is continuous, meaning that losing about 100 hairs per day on average is normal. (6)

 

Signs and symptoms of poor skin/hair health.  Indicators of comorbidity or underlying medical problems.  How stress or environmental factors affects hair health

Hair has many areas of clinical significance which include diseases of hair loss, excess, alterations due to nutritional deficiencies, infectious causes, and effects of drug reactions. The unwanted loss of hair, known as alopecia, is a widespread condition affecting both sexes, occurring in numerous patterns, and classified into non-scarring and scarring (cicatricial) subtypes. (4)

The most common non-scarring type of alopecia is androgenetic or “pattern” hair loss which develops due to a combination of genetic predisposition. This condition is also known as female or male pattern hair loss and is caused by androgens in genetically susceptible women and men. Androgenetic alopecia means that there is a genetic predisposition to reduced hair volume. It is characterized by progressive hair loss, especially of scalp hair, and has distinctive patterns of loss in women versus men, but in both genders the central scalp is most severely affected. It often begins around puberty, though its prevalence in this younger population is not known, and its incidence is reported to be 50% in Caucasian men and 19% in Caucasian women. The inheritance pattern is polygenic and is known to effect self-esteem and the individual’s quality of life. (18)

In this condition, hair follicles on the scalp are genetically predisposed to be sensitive to normal levels of circulating androgens, causing hair follicles to gradually shrink and produce strands of a finer diameter, also known as hair miniaturization. (4)

Approved pharmacologic treatment options are limited, but there are numerous nonprescription products claimed to be effective in restoring hair in androgenetic alopecia with no relevant scientific data. (18)

Alopecia areata is nonscarring patchy hair loss, usually on the scalp, which often has the characteristic “exclamation point” hairs that are short and broken and appear to be floating exclamation marks. It may be patchy, involve the entire scalp (alopecia totalis) or the whole body (alopecia universalis). (4)

Patients may recover spontaneously, but the disorder can follow a course of recurrent relapses or result in persistent hair loss. Alopecia areata can cause great psychological distress, and the most important aspect of management is counseling the patient about the unpredictable nature, chronicity and course of the condition as well as the available effective treatments, with details of their side effects. (17)

Scarring alopecia can arise from cutaneous manifestations of lupus, auto immune or a bacterial inflammatory condition known as dissecting folliculitis. These patterns of alopecia exhibit patches of shiny, bare scarring tissue on the scalp, or, bare skin and result in permanent hair loss in the affected areas. (4)

Telogen Effluvium is when hair roots are pushed into the telogen resting phase. This usually occurs after some stress, poor diet, hypo or hyperthyroidism, anemia, some specific types of pharmaceutical drugs, illness, post-pregnancy and cessation of contraceptive pill and can be acute or chronic. (4)

Traction alopecia is caused by hair under strain and is seen in people who wear their hair and tight braids and ponytails, cornrows and hair extensions. (4)

Hair loss can also be due to an infection, like tinea capitis, a fungal infection that results in a patch of hair loss on the scalp. (4)

 

Psycho-social influences/fashion/ trends/issues

Hair plays an important role in determining self-image, social perceptions, and psychosocial functioning in both men and women. Several authors confirm that the experience of hair loss is psychologically damaging, causing intense emotional suffering, and often leading to personal, social, and work-related problems. People with severe hair loss are more likely to experience psychological distress than those with mild hair loss. The loss of hair changes a person’s looks, particularly when the eyelashes and eyebrows are affected. (20)

The relationship between hair loss and psychosocial consequences may be complicated by hair loss that can arise from a stressful life event, which leads to further distress, anxiety, and depression. Women who experience high levels of stress are 11 times more likely to experience hair loss than those who do not report high stress levels. (20)

Compared with the general population, people with hair loss have an increased prevalence of psychiatric disorders, including a major depressive episode, an anxiety disorder, social phobia, or a paranoid disorder. Anxiety and depression caused by hair loss can be treated using cognitive behavioural therapy and support groups, as well as by medication such as antidepressants. Psychological treatment is important for people with hair loss, but the best method is not certain and will differ from patient to patient. Research has predominantly been focused on the general issues of coping with hair loss rather than on specific psychological treatment strategies. (20)

The most important effect is a loss of self-confidence. This is enhanced by an insecure or ambivalent attachment pattern. Two psychiatric syndromes that are most mentioned is most studies is: the body dysmorphic syndrome (very slight or imaginary defect in appearance) and trichotillomania. Androgenetic alopecia leads to an important suffering in women mostly, since men deal with this condition by shaving their hair. Alopecia induced by cancer chemotherapy has been reported to cause changes in self-concept and body image, since that sometimes hair does not return to the previous state after regrowth of hair for a majority of patients. Alopecia areata has an important psychiatric comorbidity: mostly anxiety and depression. (21)

Self-consciousness about body image is consistently portrayed and commented upon in the media. The role of the media in emphasising an expectation of a full head of hair should be explored, as well as how it can be used to educate society about hair loss and tolerance of people’s physical differences. (20)

 

Hair care: for normal scalp and hair conditions, dry scalp conditions and oily scalp conditions.    ‘Handy Hints’ for hair and scalp care

Every woman and man need hair care and cosmetics in this area are widely available, although the medical literature is rather scarce in this field. Excessive or repeated chemical treatments, grooming habits, and environmental exposure produce changes in hair texture and if extreme can result in hair breakage, tangling and frizz. If the cuticle is removed, the exposure of the cortex and further cortex damage may lead to hair fiber fracture, so the use of hair cosmetics may restore hair cuticle damage temporarily and prevent hair breakage by reducing friction. (22)

Shampoo must aim to cleanse the scalp more than the hair. Many scalp diseases are treated by active ingredients that are added to the shampoo’s formulations. It is desirable that whatever may the disease or condition be (dermatitis, seborrhea, alopecia, psoriasis), the hair strands are kept aesthetically presentable, preserving its softness, combability and shine while treating the scalp. (22)

Shampoos are typically composed of 10–30 ingredients that are grouped into: cleansing agents, conditioning agents and special care ingredients, designated to treat specific problems, such as dandruff and greasy hair. Although considered as safe products, very rarely, shampoos can cause contact dermatitis. (22)

The use of anti-dandruff shampoos can make hair more difficult to comb. High cleansing shampoos remove surface oils and increase chargeability by depositing small amounts of anionic surfactants onto the hair. Less frizz is achievable by lubricating the fiber surface and decreasing static charge with conditioners, deep conditioners and leave in products. (22)

Conditioners are used to decrease friction, detangle the hair, minimize frizz and improve combability. Conditioners act by neutralizing the electrical negative charge of the hair fiber from the shampoo by adding positive charges and by lubricating the cuticle to ease the process of detangling hair. They contain anti-static and lubricating substances that are divided into 5 main groups: polymers, oils, waxes, hydrolyzed aminoacids and cationic molecules. Depending on the capacity of entering the fiber, the conditioner may reach the cuticle surface or the inner part of the cortex. (22)

Deep conditioners most of the times contain more concentrated ingredients or just more viscosity. Some polymers are reported to build-up the hair and to resist shampooing from hair. Leave in creams, gel or mousse are designed to be applied on wet or dry hair and left without rinsing. They are aqueous based or alcohol-water solvent systems and these products act by enhancing interfiber forces and by providing a detangling effect to facilitate combing and style retention. (22)

The small angle of the waves of very curly hair makes it more susceptible to damage, making curly hair more difficult to comb without breakage. Wavy, curly and afro hair are more prone to have oily scalp but dryer hair fiber, while fine straight hair can transport sebum very well throughout the hair fibre. Abrasion and friction are important factors that cause hair damage by protein loss, so the use of conditioners with oils and silicones are important to minimize the rubbing and friction of the cuticle cells for chemical treated hair and after the use of anti-dundruff shampoos. (22)

A good hair care routine should mean that the entire scalp has been rubbed with the shampoo from the front to the back, and small amounts of shampoo had been applied on each region of the head under the hair. Appling the shampoo on the top of the head will increase hair friction and cause hair tangling. After full rinse of the shampoo, the conditioner and/or deep conditioner should be applied on the hair length avoiding the scalp. The conditioner has to be completely rinsed out. Wet hair is more fragile so it is recommended that every step should be very gentle; the shampooing, towel drying and brushing/combing. If the hair is wavy or curly, leave-in products should be used while hair is wet to increase texture and shine while drying. Grooming with a hair dryer or flat iron requires a heat protector that will spread the heat along the hair fiber surface avoiding water boiling and the development of hair. (22)

Although using a hair dryer causes more surface damage than natural drying, some scientific articles concluded that using a hair dryer at a distance of 15 cm with continuous motion causes less damage than drying hair naturally, since it’s less time exposed to the swelling caused by water. (22)

Marta Teixeira

Marta Teixeira

Adult Nursing Degree, BSc (Hons)

Postgraduate Certificate Anaesthetic Course

Trichology Certificate Course by the International Association of Trichologists

MSc in Dermatology in Clinical Practice

Non-Medical Prescribing V300 Course

 

 

References

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‌10 – de Gálvez, M.V., Aguilera, J., Bernabó, J.-L., Sánchez-Roldán, C. and Herrera-Ceballos, E. (2015). Human Hair as a Natural Sun Protection Agent: A Quantitative Study. Photochemistry and Photobiology, [online] 91(4), pp.966–970. Available at: https://pubmed.ncbi.nlm.nih.gov/25682789/ [Accessed 14 Dec. 2021].

11 – Vij, K. (2011). Textbook of Forensic Medicine and Toxicology : Principles and Practice, 5/e. [online] Google Books. Elsevier India. Available at: https://books.google.es/books/about/Textbook_of_Forensic_Medicine_and_Toxico.html?id=pOd2EVL5xAwC&redir_esc=y [Accessed 14 Dec. 2021].

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15 – Westgate, G.E., Ginger, R.S. and Green, M.R. (2017). The biology and genetics of curly hair. Experimental Dermatology, 26(6), pp.483–490.

16 – Cloete, E., Khumalo, N.P. and Ngoepe, M.N. (2019). The what, why and how of curly hair: a review. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 475(2231), p.20190516.

‌17 – Garg, S. and Messenger, A.G. (2009). Alopecia Areata: Evidence-Based Treatments. Seminars in Cutaneous Medicine and Surgery, 28(1), pp.15–18.

‌18 – Varothai, S. and Bergfeld, W.F. (2014). Androgenetic Alopecia: An Evidence-Based Treatment Update. American Journal of Clinical Dermatology, [online] 15(3), pp.217–230. Available at: https://link.springer.com/article/10.1007%2Fs40257-014-0077-5. [Accessed 14 Dec. 2021].

19 – Alfonso, M., Richter-Appelt, H., Tosti, A., Viera, M.S. and García, M. (2005). The psychosocial impact of hair loss among men: a multinational European study. Current Medical Research and Opinion, 21(11), pp.1829–1836.

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‌22 – Gavazzoni Dias, M.F. (2015). Hair cosmetics: An overview. International Journal of Trichology, [online] 7(1), p.2. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4387693/.  [Accessed 15 Dec. 2021].

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