Why is hair curly?—Deductions from the structure and the biomechanics of the mature hair shaft

The final shape of a head hair is predetermined through a variety of factors during its formation in the follicle. These are genetic pathways, specific growth factors, cell differentiation and segregation, etc, with spatial as well as chronological dynamics. The cortex of hair consists of two major cell groups. These are characterized by parallel (para-type) or roughly helical arrangements (ortho-type) of the intermediate filaments (IF). There are also cell-specific differences in the disulphide content, that is, of the cross-link density of the IF-associated matrix proteins. Given the current state of the academic discussion, we consider it as timely to support and broaden the view that, the structural differences of the cell types together with their lateral segregation are the main driving factor of curl formation. The mechanical effects, which derive thereof, are triggered in the transition zone of the follicle, that is, upon formation of the mature hair shaft. Furthermore, an irregular, “flat” cross section of the hair shaft is shown to be a synergistic but not determining factor of curl formation. The degree of cell type segregation along the mature hair shaft together with dynamic changes of the location of the plane of segregation, namely in a non-circular cross section can account for very complex curl patterns. Against the background of these views, we argue that contributions to hair curl are implausible, if they relate to physical mechanisms which are active below the transition zone from the living to the mature (dead) hair.     

Red hair − a desirable mutation?

Red hair is one of the most striking variants of human hair coloration and has historically been of profound social importance. Red hair in man is due to certain loss of function mutations of one of the peptide products of the pro-opiomelanocortin (POMC) gene, the melanocortin-1 receptor (MC1R, MIM 155555). Such functional mutations enable the melanocyte to produce red-yellow pheomelanin in preference to the default, black-brown eumelanin. This paper reviews the path of discovery of the MC1R in control of animal coat colour, the subsequent role of MC1R in human physiology and possibly wider role of MC1R in human skin carcinogenesis and human development through history.     

Kenogen. A new phase of the hair cycle?

BACKGROUND: A novel phenomenon has been described by the phototrichogram: the emptiness of the follicle after teloptosis. We called this phenomenon kenogen, from the Greek kappaepsilonnuóvarsigma, 'empty'. OBJECTIVE: To describe the kenogen phase in its details. METHODS: Analysis of the existing literature. RESULTS: The original observation in 2 women was confirmed in 10 balding and non-balding males studied for 14 years in whom kenogen lasted about 4 months increasing up to about 7 months and affecting 80% of all hair cycles. In 2 women with progressing androgenetic alopecia studied for 2 years, kenogen involved 22% of the hair follicles, lasting from 3 months to 1 year. In a prepubertal boy studied for 1 year, it involved 8% of hairs and lasted about 2 months. CONCLUSION: During kenogen, the hair follicle rests physiologically, but duration and frequency are greater in androgenetic alopecia, possibly accounting for baldness. In addition to the classical cycle, the hair follicle may follow an alternative route during which the telogen phase, not accompanied by a coincident new early anagen, ends with teloptosis leaving the follicle empty.     

Baseline sebum IL‐1α is higher than expected in afro‐textured hair: a risk factor for hair loss?*

Objective To investigate changes in sebum cytokines in response to hair cosmetics. Design and setting A prospective study at a University hospital. Methods We used a novel method for scalp surface sebum collection (Sebutape^®) on three visits, sequentially a week apart, to investigate changes in six cytokines in 36 healthy women before and after shampoo and compared various chemical treatments (ammonium thioglycolate, “lye” sodium hydroxide and “no‐lye” guanidine hydroxide relaxers) performed by a professional hairdresser. Results Significant levels detected were IL‐1 alpha (IL‐1α) and IL‐1 receptor antagonist (IL‐1ra), which were higher in untreated scalp vs. forehead: P < 0.001. Baseline levels of scalp sebum IL‐1α were 18 times higher than IL‐1ra. The levels of IL‐1α decreased uniformly after shampoo (visit 1) and various chemical treatments (both crown and vertex all P < 0.001 – visit 2) but increased on follow‐up at visit 3. Decreases in IL‐1ra mimicked IL‐1α at the vertex [after shampoo (P = 0.018) and visit 3 (P = 0.014)], but not on the crown, a finding which may suggest site‐specific scalp predisposition to inflammation. The ratio of IL‐1ra/IL‐1α increased in all groups after all chemical treatments and on follow‐up (all P < 0.001) but was surprisingly not significantly different from natural hair that underwent shampoo. Limitations A wider cytokine panel may reveal response differences in treatment groups. Conclusions Baseline inflammatory scalp cytokines are higher than expected and reduce with shampooing. Scrutiny of the influence of hair moisturizer formulations and shampoo intervals and studies investigating pro‐fibrotic cytokines are required. This may elucidate the predilection of afro‐textured hair to scarring alopecia.     

Mechanobiology and cell tensegrity: the root of ethnic hair curling?

Background The hair shape, either straight, crimp, or curly, is basically under genetic influence. It is possibly altered by some drugs such as cytostatic agents. In addition, specific innate molecular characteristics are modulated by some cosmetic procedures to reshape the hair shafts. Aim To revisit the possible implication of mechanobiology and cell tensegrity in shaping ethnic hair. Materials and methods Optical and scanning electron microscopy of hairs. Results It is generally held that the cross‐section shape of hair is related to differences in the global aspect of the hair shaft. A possible biologic link between these features may rely on shaping cell tensegrity at any portion of the hair shaft. Cell tensegrity encompasses all intrinsic and extrinsic forces responsible for the three‐dimensional arrangement of intracellular macromolecules. Conclusion We offer as a hypothesis that the hair shape in part depends on the organization of the cell proliferation in the hair matrix. This review gathers observations supporting the involvement of cell tensegrity in shaping the hair shaft.     

Complications of laser hair removal—How we could reduce them?

Laser hair removal became a very popular intervention, with a permanently increasing number of procedures being performed worldwide. The procedure is often performed by nonmedical personnel, and even by untrained personnel, that could be associated with different kind of adverse events, from mild to serious. The complications associated could be lower if the operators understand the basic of laser physics and the working principles of devices. We propose a simple acronym, WATCH, in order to increase the safety and efficiency of laser interventions.     

Is the loose anagen hair syndrome a keratin disorder? A clinical and molecular study

OBJECTIVES: To report the clinical features of the loose anagen hair syndrome and to test the hypothesis that the typical gap between the hair and the inner root sheath may result from hereditary defects in the inner root sheath or the apposed companion layer. DESIGN: Case series. SETTING: A pediatric dermatology unit (referral center). PATIENTS: A consecutive sample of 17 children (13 girls). For 9 of them and their first-degree relatives, molecular analyses were performed in the K6HF gene with 50 appropriate controls. INTERVENTION: Minoxidil therapy (5% lotion) in 11 patients for 1 to 12 months. MAIN OUTCOME MEASURES: Clinical and follow-up features and determination of mutations in the K6HF gene. RESULTS: Most patients had easily pluckable hair with no sign of scalp inflammation or scarring. Ten patients seldom cut their hair, and 4 had unmanageable hair. One patient had hypodontia. Two patients had an additional clinical phenotype of diffuse partial woolly hair. The family history was positive for loose anagen hair syndrome in 5 patients. Marked improvement was noted after treatment with 5% minoxidil lotion in 7 of the 11 patients treated. Polymerase chain reaction analysis of the gene segments encoding the alpha-helical 1A and 2B subdomains of K6hf, the type II cytokeratin exclusively expressed in the companion layer, was performed in 9 families. In 3 of these 9 families, a heterozygous glutamic acid and lysine mutation, E337K, was identified in the L2 linker region of K6HF. CONCLUSIONS: Diffuse partial woolly hair can be associated with loose anagen hair syndrome. A keratin mutation, E337K in K6HF, was possibly causative in 3 of the 9 families studied. Another keratin, and possibly the type I partner of K6hf, could be responsible for loose anagen hair syndrome in other patients, or the gene involved may be a minor gene.     

Platelet rich plasma for the management of hair loss: Better alone or in combination?

Platelet‐rich plasma (PRP) and autologous protein‐based treatments have recently emerged as a potential therapeutic approach for hair loss‐related disorders including androgenetic alopecia and alopecia areata. The safety and efficacy of repeated intradermal injections of PRP has proved to promote hair growth in a number of randomized clinical trials. Biologically active proteins and cytokines released upon platelet activation have shown to induce folliculogenesis and activate the anagen growing phase of dormant bulbs. Interestingly, further studies have revealed that combining PRP with other hair loss‐related products may enhance the final performance of the treatment. These synergistic approaches include Food and Drug Administration (FDA) approved drugs such as finasteride or minoxidil, bioactive macromolecules and cell‐based therapies. Here, recent research involving alone or combined therapy with platelet‐rich plasma for the management of hair loss‐related disorders are outlined and future prospects are discussed.     

What s new in hair transplants?

As hair transplant surgery has evolved, combinations of micrografting and minigrafting have enabled physicians to produce ever more natural combinations of both. A wide range of men and women can now receive significant aesthetic benefits from hair transplants. In recent years, practitioners have further refined hair transplant techniques to ensure that the hairs available for transplantation are used most efficiently. Specifically, methods of harvesting hair, preparing grafts, creating recipient sites, and placing grafts are designed to permit the maximum percentage of hairs to survive and thrive after transplantation. Careful planning, close cooperation with the patient, and a staged surgical approach can also result in hair conservation and optimal cosmesis.     

Do androgens influence hair growth by altering the paracrine factors secreted by dermal papilla cells?

Androgens regulate many aspects of human hair growth in both sexes. After puberty they transform tiny vellus follicles in many areas, e.g. the face, to terminal ones producing long, thick, pigmented hairs. In genetically predisposed individuals, androgens also cause the reverse transformation of terminal scalp follicles into vellus ones, causing balding. In the current hypothesis for androgen action, androgens control most follicular cells indirectly acting via the mesenchyme-derived dermal papilla which regulates many aspects of follicular activity. In this model androgens binding to androgen receptors in dermal papilla cells alter their production of regulatory molecules which influence other follicular components; these molecules may be soluble paracrine factors and/or extracellular matrix proteins. This hypothesis is supported by immunohistochemical localisation of androgen receptors in dermal papilla cell nuclei and the demonstrations that androgen receptor content and testosterone metabolism patterns of cultured dermal papilla cells from various body sites reflect hair growth in androgen-insensitivity syndromes. The next question is whether androgens alter the paracrine factors secreted by dermal papilla cells. Cultured dermal papilla cells do release soluble, proteinaceous factors into their media which stimulate the growth of keratinocytes and other dermal papilla cells. This mitogenic potential can cross species from humans to rodents. Importantly, testosterone in vitro stimulates the mitogenic potential of beard cells, but in contrast inhibits production by balding scalp cells reflecting their in vivo androgenic responses. Since androgens in vitro do alter the secretion of paracrine factors the current focus lies in identifying specific factors produced, e.g. IGF-I and stem cell factor (SCF), using ELISA and RT-PCR, and comparing their expression in cells from follicles with varying responses to androgens in vivo or under androgen stimulation in vitro. This should lead to greater understanding of androgen action and enable the development of better treatment for androgen-potentiated disorders.     

What is new in genetically-induced hair diseases?

A profound knowledge of specific genetically determined anomalies of the hair may be of considerable value in the diagnosis of genetic syndromes. We give a review of a few recent developments in the field of genetic hair diseases. For example, the brittle hair due to sulphur deficiency (trichothiodystrophy) is nowadays regarded as genetically heterogeneous; three different syndromes can be distinguished: BIDS syndrome, Tay syndrome, and PIBIDS syndrome. Polarization microscopy revealed a striking resemblance of the hair anomalies found in trichothiodystrophy syndromes and those in acrodermatitis enteropathica. This surprising result indicates similar pathophysiological mechanisms. The Comèl-Netherton syndrome--long regarded as representing two different diseases--has recently been recognized as a clinically variable, but genetically homogeneous syndrome, which is most likely based on a single mutation ("lumping"). Minor's sweat test allows the recognition of women heterozygous for X-linked hypohidrotic ectodermal dysplasia and may help to appreciate seemingly non-specific hair findings, such as diffuse alopecia.     

The phenomen of sudden graying of the hair in the poem "Die Füsse im Feuer" by Conrad Ferdinand Meyer

In his poem "Die Füsse im Feuer" Conrad Ferdinand Meyer (1825-1898) describes in detail the phenomenon of sudden graying of the hair. The protagonist is a Huguenot nobleman who hosts the man who has tortured to death his wife some years ago without killing him despite ample opportunities. Sudden whitening of the hair has been used as literary stylistic means with the aim to demonstrate extreme psychological stress to the world, without confirmation of its occurrence in each case.