Androgenetic alopecia and microinflammation
Yann F. Mahé,PhD, Jean-François Michelet,MSc, Nelly Billoni, MSc, Françoise Jarrousse, BTS , Bruno Buan, BTS , Stephane Commo, BTS, Didier Saint-Léger,PhD and Bruno A. Bernard,PhD
International Journal of Dermatology
Volume 39 Issue 8 Page 576 - August 2000
Today, androgenetic alopecia (Androgenetic Alopecia) is considered to be an alteration of hair growth and/or a premature aging of the pilosebaceous unit with a multifactorial and even polygenic etiology. 1 The fact that the success rate of treatment with either antihypertensive agents, or modulators of androgen metabolism, barely exceeds 30% means that other pathways may be envisioned. The implication of various activators of inflammation in the etiology of Androgenetic Alopecia has progressively and recently emerged from several independent studies. 2,3,4,5,6,7,8,9,10,11 A fibroplasia of the dermal sheath, which surrounds the hair follicle, is now suspected to be a common terminal process resulting in the miniaturization and involution of the pilosebaceous unit in Androgenetic Alopecia. 2 8 We review here several observations underlining the possible implication of a slow, silent, and painless process in Androgenetic Alopecia. Because we think that it should not be confused with a classical inflammatory process, we have called it microinflammation. An early study referred to an inflammatory infiltrate of mononuclear cells and lymphocytes in about 50% of the scalp samples studied. 2 Another more recent study by Jaworsky et al . 3 confirmed an inflammatory infiltrate of activated T cells and macrophages in the upper third of the hair follicles from transitional regions of alopecia (i.e. which are characterized by actively progressing alopecia). This study also reported the occurrence of a developing fibrosis of the perifollicular sheath, together with the degranulation of follicular adventitial mast cells. The miniaturization of the hair follicles was found to be associated with a deposit of so-called "collagen or connective tissue streamers" beneath the follicle, 2,7 as well as a 2 2.5 times enlargement of the follicular dermal sheath composed of densely packed collagen bundles. 3 This thickening of the dermal sheath in progression zones of Androgenetic Alopecia has also recently been observed in our laboratory using immunohistochemical staining ( Fig. 1 ).
Horizontal section studies of scalp biopsies indicate that the so-called perifollicular fibrosis is generally mild, consisting of loose, concentric layers of fibrotic collagen that must be distinguished from cicatricial alopecia. 4 It is unclear whether or not the fibrosis seen in follicular streamers (stelae or fibrous tracts) is permanent and/or alters the downgrowth of anagen hair follicles. Only 55% of male pattern Androgenetic Alopecia patients with microinflammation had hair regrowth in response to minoxidil treatment, which was less than the 77% of patients with no signs of inflammation, 4 suggesting that, to some extent, perifollicular microinflammation may account for some cases of male pattern Androgenetic Alopecia which do not respond to minoxidil. 4 Another study on 412 patients (193 men and 219 women) confirmed the presence of a significant degree of inflammation and fibrosis in at least 37% of Androgenetic Alopecia cases. 5 The upper location of the infiltrate near the infrainfundibulum 2 7 clearly distinguishes Androgenetic Alopecia from alopecia areata (AA), the latter disease being characterized by infiltrates in the bulb and dermal papilla zone. 12
The aim of this review is to determine the location and chronology of the microinflammation process within the complex pathophysiology of the human pilosebaceous unit in order to improve the possible approaches for the reduction or prevention of the development of Androgenetic Alopecia.
Classically, an inflammatory process is ascribed to a central major mediator or pathway. Such a monofactorial vision has been historically well exemplified by the famous interleukin-1 (IL-1) scheme developed by Oppenheim et al . 13 which is still valid even after 13 years. In fact, many inflammatory agents are at the center of a huge array of effects, involving cells, enzymes, adhesion molecules and other biological mechanisms. The identification of the effects of isolated factors is only part of the problem; it may be more important to determine when and where the individual factors are involved in the complex sequence. This pathway has been clearly identified, and several inhibitory anti-inflammatory drugs acting on this aspect of inflammation have been developed and clinically evaluated. 14,15 , 16,17
The cytokine/chemokine side of microinflammation
Why does microinflammation take place in the pilosebaceous unit and for what benefit and purpose? Fig. 2 and Fig. 3 show, in a simplified sequence, that inflammation is a multistep process which may start from a primary event. Let us look at the clues at the "crime scene" of Androgenetic Alopecia: we observe a perifollicular infiltrate in the upper follicle near the infundibulum. 2 7 This suggests that the primary causal event for the triggering of inflammation might occur near the infundibulum. 3,7 Supporting this point of view, improvement of the inflammatory aspect of Androgenetic Alopecia has been reported in a pilot study with an antimicrobial lotion. 7 One could speculate that several inhabitants of the scalp, such as the "triad" ( Propionibacterium sp.; Staphylococcus sp.; Malassezia ovalis ) or other members of the transient flora, could be involved in this complex inflammatory process. 7 The presence of porphyrins (produced by Propionibacterium sp.) in the pilosebaceous duct of 58% of Androgenetic Alopecia patients (compared with 12% of control subjects), which are able to induce the production of complement (C5) chemotactic factor, is considered to be a possible cofactor of this initial pro-inflammatory stress. 6,7 Keratinocytes are also known to respond within minutes to chemical stress, pollutants, UV irradiation or even mechanical stress. 37 Not only are radical oxygen species, 38 NO, 39 PGs, and histamine 40 produced, but also intracellularly stored IL-1 is released 37,41 (see Fig. 2 and step 1 of Fig. 3 ). By itself, this pro-inflammatory cytokine (as well as IL-1 which binds to the same receptor) is able to inhibit the growth of isolated hair follicles in culture in vitro. 9 11 This concentration-dependent inhibition of human hair elongation and survival indicates a high sensitivity to IL-1 of the isolated organ in culture in vitro (IC 50 = 10 pg/mL 11 ). In vivo , transgenic mice which overexpress IL-1 in the basal epidermis and in the outer root sheath of their pelage hair follicles exhibit a spontaneous cutaneous phenotype characterized by a sparseness of hair. 42 As a response to an IL-1 signal, adjacent keratinocytes which express receptors for IL-1 start to engage the transcription of IL-1 responsive genes 41 ( Fig. 3 , step 2). In vitro , following IL-1 stimulation, this transcriptional activation cascade is induced within 6 h in plucked human hair follicles. 11
Alternatively, skin keratinocytes, which may also have antigen presenting capabilities, could theoretically induce T-cell proliferation in response to bacterial antigens. 51 These antigens, once they have been "tagged," are then selectively destroyed by infiltrating macrophages, Langerhans cells, or natural killer cells. 50,52 On many occasions, however, the causal agent persists, resulting in sustained inflammation ( Fig. 3, step 4). This corresponds partly to the situation which has been pictured in the progression zone of roughly one-third of alopecia cases: infiltrating T lymphocytes, together with mastocytes and macrophages, located in the upper perifollicular adventitial dermal sheath perpetuate a local inflammatory stage. 27 This phase of inflammation often results in tissue remodeling, where collagenases, such as matrix metalloproteinase (MMP)-9 (transcriptionally activated by pro-inflammatory cytokines) or MMP-8 (directly produced by infiltrating cells), may play an active role. 5355 Thus, collagenases are suspected to contribute to the tissue changes and the so-called "perifollicular fibrosis" by "preparing" tissue matrix and basal membranes for macrophages and T-cell adhesion. Accordingly, this scenario facilitates the secretion of membrane-anchored cytokines, such as TNF-. 55 Other factors, such as MCP-1, have been directly suspected to contribute to organ fibrosis in an experimental model of renal inflammation. 56 As MCP-1, together with other chemokines, was found to be expressed in human hair follicles in vitro, 11 as well as in the eccrine ducts of sebaceous glands in vivo, 57 it might also be actively involved in the progression of perifollicular fibrosis detected in Androgenetic Alopecia. 26 The development of perifollicular fibrosis might thus appear as the signature of a disequilibrium between pro-and anti-inflammatory pathways.
Relations between inflammation and steroidogenesis: the missing link
There is no question that androgens are major modulators of hair loss. Recently, it was shown that testosterone inhibited the growth of outer root sheath keratinocytes only when they were cocultured with dermal papilla cells derived from the bald scalp of an adult macaque, 58 reinforcing the hypothesis of an androgen influence on hair growth via the dermal papilla. 59 The potent metabolite of testosterone (i.e. 5-dihydrotestosterone, 5-DHT) is considered as a "culprit". 60 5-DHT is generated from testosterone through the activity of 5-reductase (5-R). Two active isoforms of 5-R, which differ both in tissue site distribution as well as in optimal pH for enzymatic activity, have been identified and cloned. 61,62, 63 While the type II isoform is considered to be the major isozyme in genital tissues, 61 the type I isoform is considered to be the major isoform expressed in skin and in the pilosebaceous unit. 64,65 Isoform II, however, has recently been detected in the inner root sheath of the pilosebaceous unit by immunohistochemistry, 66,67 Northern blotting, 67 and the pH dependence of optimal enzymatic activity. 67 Thus, the contribution of both isoforms in the regression of the pilosebaceous unit is still a matter of debate. Recently, a clinical study using finasteride, a strong inhibitor of 5-RII (and weak inhibitor of 5-RI), showed that intervention in androgen metabolism could, to some extent, modulate the progression of Androgenetic Alopecia, when the drug was given by the oral route, 68 but not topically. 69 After oral ingestion, an improvement of hair growth was observed, which was associated with a drastic reduction of serum levels of 5-DHT, corresponding to those observed in castrates. 68 Despite such a reduction of circulating 5-DHT levels, however, a number of individuals (60-70%) still remained unresponsive to this treatment, indicating again that simple dysregulation of 5-DHT synthesis levels or a genetic polymorphism of 5-R genes cannot account for all cases of Androgenetic Alopecia, and a polygenic etiology should be considered. 1
Thus, to date, the only evident link that can be established between androgen metabolism and the complex inflammatory process is sebum production which is controlled by androgens. 70 As sebum harbors a large amount of microorganisms which use lipids as nutrients, 8 it cannot be excluded that, at least for some individuals, androgen metabolism might facilitate the colonization of the sebaceous infundibulum and sebaceous ducts by such microorganisms which may be involved in the first steps of pilosebaceous unit inflammation.
We propose here working hypotheses which do not invalidate the contribution of a hereditary genetic androgen imbalance in Androgenetic Alopecia, 60 but rather attempt to integrate the neglected microinflammatory aspects of alopecia into the complex etiology of Androgenetic Alopecia. On the one hand, excessive local and/or endocrine, genetically exacerbated 5-DHT synthesis results in sebaceous gland enlargement; 2,60 as a consequence, some scalps might offer more comfortable niches to harbor the previously mentioned pro-inflammatory microorganisms. 6,7 On the other hand, androgen imbalance and metabolism may be locally exacerbated by pro-inflammatory cytokines. For example, gingival fibroblasts have been reported to modify their androgen metabolism through the action of several growth factors, such as epidermal growth factor (EGF), transforming growth factor beta (TGF-), and the pro-inflammatory cytokines IL-1 and TNF-. 71 Therefore, one could speculate that, once the inflammatory process has been triggered, the androgenetic mechanism of alopecia could subsequently be locally amplified. This upregulation of androgen metabolism by pro-inflammatory cytokines remains, however, to be established at the pilosebaceous unit level.
Our visit to the "crime scene" of Androgenetic Alopecia yielded many clues ( Fig. 4 ). We know now that, at least in about one-third of cases, the tool which causes the lethal damage is a microinflammatory process. Several factors are present, however, which are suspected to have handled the tool: androgens, microbial flora, endogenous or exogenous stress, genetic imbalance, and possibly others. Although other suspects or tools are likely to be discovered in the future, it cannot be excluded that, for each individual, the causal agent, as well as the sequence of events or combined factors, may be different. The large number of molecules claimed to be active and patented in this field, 89 and their limited efficacy in offering a definite and extensive cure of Androgenetic Alopecia, confirm that the mechanism of Androgenetic Alopecia is highly complex. Accordingly, it appears that, due to the complexity and multiple interactivities and cooperations involved throughout the distinct inflammatory pathways (partly described in Fig. 2 ), an anti-inflammatory strategy should be targeted to the appropriate effector(s) at the right moment. For this purpose, we have developed a simple assay to evaluate individuals with potentially affected hair follicles. 11 We observed that plucked hair specimens of 33% of the 116 volunteers evaluated could be classified as highly inflammatory in terms of spontaneous IL-1 production. 11 Consequently, the identification of the "inflammatory alopecic individuals" may help to adapt the right answer to the right cause. Such a selective approach might be valuable for other parameters, such as an imbalance in 11 HSD activity, 5-DHT synthesis, or microorganism colonization. Encompassing individual diversity is thus a prerequisite for appropriately addressing the biological conditions contributing to Androgenetic Alopecia. Our findings and a review of the literature suggest that inflammation in its diversity is a potentially active player to consider in this approach.
Yann F. Mahé,PhD, Jean-François Michelet,MSc, Nelly Billoni, MSc, Françoise Jarrousse, BTS , Bruno Buan, BTS , Stephane Commo, BTS, Didier Saint-Léger,PhD and Bruno A. Bernard,PhD
International Journal of Dermatology
Volume 39 Issue 8 Page 576 - August 2000
Today, androgenetic alopecia (Androgenetic Alopecia) is considered to be an alteration of hair growth and/or a premature aging of the pilosebaceous unit with a multifactorial and even polygenic etiology. 1 The fact that the success rate of treatment with either antihypertensive agents, or modulators of androgen metabolism, barely exceeds 30% means that other pathways may be envisioned. The implication of various activators of inflammation in the etiology of Androgenetic Alopecia has progressively and recently emerged from several independent studies. 2,3,4,5,6,7,8,9,10,11 A fibroplasia of the dermal sheath, which surrounds the hair follicle, is now suspected to be a common terminal process resulting in the miniaturization and involution of the pilosebaceous unit in Androgenetic Alopecia. 2 8 We review here several observations underlining the possible implication of a slow, silent, and painless process in Androgenetic Alopecia. Because we think that it should not be confused with a classical inflammatory process, we have called it microinflammation. An early study referred to an inflammatory infiltrate of mononuclear cells and lymphocytes in about 50% of the scalp samples studied. 2 Another more recent study by Jaworsky et al . 3 confirmed an inflammatory infiltrate of activated T cells and macrophages in the upper third of the hair follicles from transitional regions of alopecia (i.e. which are characterized by actively progressing alopecia). This study also reported the occurrence of a developing fibrosis of the perifollicular sheath, together with the degranulation of follicular adventitial mast cells. The miniaturization of the hair follicles was found to be associated with a deposit of so-called "collagen or connective tissue streamers" beneath the follicle, 2,7 as well as a 2 2.5 times enlargement of the follicular dermal sheath composed of densely packed collagen bundles. 3 This thickening of the dermal sheath in progression zones of Androgenetic Alopecia has also recently been observed in our laboratory using immunohistochemical staining ( Fig. 1 ).
Horizontal section studies of scalp biopsies indicate that the so-called perifollicular fibrosis is generally mild, consisting of loose, concentric layers of fibrotic collagen that must be distinguished from cicatricial alopecia. 4 It is unclear whether or not the fibrosis seen in follicular streamers (stelae or fibrous tracts) is permanent and/or alters the downgrowth of anagen hair follicles. Only 55% of male pattern Androgenetic Alopecia patients with microinflammation had hair regrowth in response to minoxidil treatment, which was less than the 77% of patients with no signs of inflammation, 4 suggesting that, to some extent, perifollicular microinflammation may account for some cases of male pattern Androgenetic Alopecia which do not respond to minoxidil. 4 Another study on 412 patients (193 men and 219 women) confirmed the presence of a significant degree of inflammation and fibrosis in at least 37% of Androgenetic Alopecia cases. 5 The upper location of the infiltrate near the infrainfundibulum 2 7 clearly distinguishes Androgenetic Alopecia from alopecia areata (AA), the latter disease being characterized by infiltrates in the bulb and dermal papilla zone. 12
The aim of this review is to determine the location and chronology of the microinflammation process within the complex pathophysiology of the human pilosebaceous unit in order to improve the possible approaches for the reduction or prevention of the development of Androgenetic Alopecia.
Classically, an inflammatory process is ascribed to a central major mediator or pathway. Such a monofactorial vision has been historically well exemplified by the famous interleukin-1 (IL-1) scheme developed by Oppenheim et al . 13 which is still valid even after 13 years. In fact, many inflammatory agents are at the center of a huge array of effects, involving cells, enzymes, adhesion molecules and other biological mechanisms. The identification of the effects of isolated factors is only part of the problem; it may be more important to determine when and where the individual factors are involved in the complex sequence. This pathway has been clearly identified, and several inhibitory anti-inflammatory drugs acting on this aspect of inflammation have been developed and clinically evaluated. 14,15 , 16,17
The cytokine/chemokine side of microinflammation
Why does microinflammation take place in the pilosebaceous unit and for what benefit and purpose? Fig. 2 and Fig. 3 show, in a simplified sequence, that inflammation is a multistep process which may start from a primary event. Let us look at the clues at the "crime scene" of Androgenetic Alopecia: we observe a perifollicular infiltrate in the upper follicle near the infundibulum. 2 7 This suggests that the primary causal event for the triggering of inflammation might occur near the infundibulum. 3,7 Supporting this point of view, improvement of the inflammatory aspect of Androgenetic Alopecia has been reported in a pilot study with an antimicrobial lotion. 7 One could speculate that several inhabitants of the scalp, such as the "triad" ( Propionibacterium sp.; Staphylococcus sp.; Malassezia ovalis ) or other members of the transient flora, could be involved in this complex inflammatory process. 7 The presence of porphyrins (produced by Propionibacterium sp.) in the pilosebaceous duct of 58% of Androgenetic Alopecia patients (compared with 12% of control subjects), which are able to induce the production of complement (C5) chemotactic factor, is considered to be a possible cofactor of this initial pro-inflammatory stress. 6,7 Keratinocytes are also known to respond within minutes to chemical stress, pollutants, UV irradiation or even mechanical stress. 37 Not only are radical oxygen species, 38 NO, 39 PGs, and histamine 40 produced, but also intracellularly stored IL-1 is released 37,41 (see Fig. 2 and step 1 of Fig. 3 ). By itself, this pro-inflammatory cytokine (as well as IL-1 which binds to the same receptor) is able to inhibit the growth of isolated hair follicles in culture in vitro. 9 11 This concentration-dependent inhibition of human hair elongation and survival indicates a high sensitivity to IL-1 of the isolated organ in culture in vitro (IC 50 = 10 pg/mL 11 ). In vivo , transgenic mice which overexpress IL-1 in the basal epidermis and in the outer root sheath of their pelage hair follicles exhibit a spontaneous cutaneous phenotype characterized by a sparseness of hair. 42 As a response to an IL-1 signal, adjacent keratinocytes which express receptors for IL-1 start to engage the transcription of IL-1 responsive genes 41 ( Fig. 3 , step 2). In vitro , following IL-1 stimulation, this transcriptional activation cascade is induced within 6 h in plucked human hair follicles. 11
Alternatively, skin keratinocytes, which may also have antigen presenting capabilities, could theoretically induce T-cell proliferation in response to bacterial antigens. 51 These antigens, once they have been "tagged," are then selectively destroyed by infiltrating macrophages, Langerhans cells, or natural killer cells. 50,52 On many occasions, however, the causal agent persists, resulting in sustained inflammation ( Fig. 3, step 4). This corresponds partly to the situation which has been pictured in the progression zone of roughly one-third of alopecia cases: infiltrating T lymphocytes, together with mastocytes and macrophages, located in the upper perifollicular adventitial dermal sheath perpetuate a local inflammatory stage. 27 This phase of inflammation often results in tissue remodeling, where collagenases, such as matrix metalloproteinase (MMP)-9 (transcriptionally activated by pro-inflammatory cytokines) or MMP-8 (directly produced by infiltrating cells), may play an active role. 5355 Thus, collagenases are suspected to contribute to the tissue changes and the so-called "perifollicular fibrosis" by "preparing" tissue matrix and basal membranes for macrophages and T-cell adhesion. Accordingly, this scenario facilitates the secretion of membrane-anchored cytokines, such as TNF-. 55 Other factors, such as MCP-1, have been directly suspected to contribute to organ fibrosis in an experimental model of renal inflammation. 56 As MCP-1, together with other chemokines, was found to be expressed in human hair follicles in vitro, 11 as well as in the eccrine ducts of sebaceous glands in vivo, 57 it might also be actively involved in the progression of perifollicular fibrosis detected in Androgenetic Alopecia. 26 The development of perifollicular fibrosis might thus appear as the signature of a disequilibrium between pro-and anti-inflammatory pathways.
Relations between inflammation and steroidogenesis: the missing link
There is no question that androgens are major modulators of hair loss. Recently, it was shown that testosterone inhibited the growth of outer root sheath keratinocytes only when they were cocultured with dermal papilla cells derived from the bald scalp of an adult macaque, 58 reinforcing the hypothesis of an androgen influence on hair growth via the dermal papilla. 59 The potent metabolite of testosterone (i.e. 5-dihydrotestosterone, 5-DHT) is considered as a "culprit". 60 5-DHT is generated from testosterone through the activity of 5-reductase (5-R). Two active isoforms of 5-R, which differ both in tissue site distribution as well as in optimal pH for enzymatic activity, have been identified and cloned. 61,62, 63 While the type II isoform is considered to be the major isozyme in genital tissues, 61 the type I isoform is considered to be the major isoform expressed in skin and in the pilosebaceous unit. 64,65 Isoform II, however, has recently been detected in the inner root sheath of the pilosebaceous unit by immunohistochemistry, 66,67 Northern blotting, 67 and the pH dependence of optimal enzymatic activity. 67 Thus, the contribution of both isoforms in the regression of the pilosebaceous unit is still a matter of debate. Recently, a clinical study using finasteride, a strong inhibitor of 5-RII (and weak inhibitor of 5-RI), showed that intervention in androgen metabolism could, to some extent, modulate the progression of Androgenetic Alopecia, when the drug was given by the oral route, 68 but not topically. 69 After oral ingestion, an improvement of hair growth was observed, which was associated with a drastic reduction of serum levels of 5-DHT, corresponding to those observed in castrates. 68 Despite such a reduction of circulating 5-DHT levels, however, a number of individuals (60-70%) still remained unresponsive to this treatment, indicating again that simple dysregulation of 5-DHT synthesis levels or a genetic polymorphism of 5-R genes cannot account for all cases of Androgenetic Alopecia, and a polygenic etiology should be considered. 1
Thus, to date, the only evident link that can be established between androgen metabolism and the complex inflammatory process is sebum production which is controlled by androgens. 70 As sebum harbors a large amount of microorganisms which use lipids as nutrients, 8 it cannot be excluded that, at least for some individuals, androgen metabolism might facilitate the colonization of the sebaceous infundibulum and sebaceous ducts by such microorganisms which may be involved in the first steps of pilosebaceous unit inflammation.
We propose here working hypotheses which do not invalidate the contribution of a hereditary genetic androgen imbalance in Androgenetic Alopecia, 60 but rather attempt to integrate the neglected microinflammatory aspects of alopecia into the complex etiology of Androgenetic Alopecia. On the one hand, excessive local and/or endocrine, genetically exacerbated 5-DHT synthesis results in sebaceous gland enlargement; 2,60 as a consequence, some scalps might offer more comfortable niches to harbor the previously mentioned pro-inflammatory microorganisms. 6,7 On the other hand, androgen imbalance and metabolism may be locally exacerbated by pro-inflammatory cytokines. For example, gingival fibroblasts have been reported to modify their androgen metabolism through the action of several growth factors, such as epidermal growth factor (EGF), transforming growth factor beta (TGF-), and the pro-inflammatory cytokines IL-1 and TNF-. 71 Therefore, one could speculate that, once the inflammatory process has been triggered, the androgenetic mechanism of alopecia could subsequently be locally amplified. This upregulation of androgen metabolism by pro-inflammatory cytokines remains, however, to be established at the pilosebaceous unit level.
Our visit to the "crime scene" of Androgenetic Alopecia yielded many clues ( Fig. 4 ). We know now that, at least in about one-third of cases, the tool which causes the lethal damage is a microinflammatory process. Several factors are present, however, which are suspected to have handled the tool: androgens, microbial flora, endogenous or exogenous stress, genetic imbalance, and possibly others. Although other suspects or tools are likely to be discovered in the future, it cannot be excluded that, for each individual, the causal agent, as well as the sequence of events or combined factors, may be different. The large number of molecules claimed to be active and patented in this field, 89 and their limited efficacy in offering a definite and extensive cure of Androgenetic Alopecia, confirm that the mechanism of Androgenetic Alopecia is highly complex. Accordingly, it appears that, due to the complexity and multiple interactivities and cooperations involved throughout the distinct inflammatory pathways (partly described in Fig. 2 ), an anti-inflammatory strategy should be targeted to the appropriate effector(s) at the right moment. For this purpose, we have developed a simple assay to evaluate individuals with potentially affected hair follicles. 11 We observed that plucked hair specimens of 33% of the 116 volunteers evaluated could be classified as highly inflammatory in terms of spontaneous IL-1 production. 11 Consequently, the identification of the "inflammatory alopecic individuals" may help to adapt the right answer to the right cause. Such a selective approach might be valuable for other parameters, such as an imbalance in 11 HSD activity, 5-DHT synthesis, or microorganism colonization. Encompassing individual diversity is thus a prerequisite for appropriately addressing the biological conditions contributing to Androgenetic Alopecia. Our findings and a review of the literature suggest that inflammation in its diversity is a potentially active player to consider in this approach.
