Exploring some characteristics (density, anagen ratio, growth rate) of human body hairs. Variations with skin sites, gender and ethnics

Enhancement of Skin Permeability Prediction through PBPK Modeling, Bayesian Inference, and Experiment Design

Physiologically based pharmacokinetic (PBPK) models of skin absorption are a powerful resource for estimating drug delivery and chemical risk of dermatological products. This paper presents a PBPK workflow for the quantification of the mechanistic determinants of skin permeability and the use of these quantities in the prediction of skin absorption in novel contexts. A state-of-the-art mechanistic model of dermal absorption was programmed into an open-source modeling framework. A sensitivity analysis was performed to identify the uncertain compound-specific, individual-specific, and site-specific model parameters that impact permeability. A Bayesian Markov Chain Monte Carlo algorithm was employed to derive distributions of these parameters given in vitro experimental permeability measurements. Extrapolations to novel contexts were generated by simulating the model following its update with samples drawn from the learned distributions as well as parameters that represent the intended scenario. This algorithm was applied multiple times, each using a unique set of permeability measurements sourced under experimental contexts that differ in terms of the compound, vehicle pH, skin sample anatomical site, and the number of compounds under which each subject's skin samples were tested. Among the data sets used in this study, the highest accuracy and precision in the extrapolated permeability was achieved in those that include measurements conducted under multiple vehicle pH levels and in which individual subjects' skin samples are tested under multiple compounds. This work thus identifies factors for consideration in the design of experiments for the purpose of training dermal models to robustly estimate drug delivery and chemical risk.

The hair follicle-psoriasis axis: Shared regulatory mechanisms and therapeutic targets

It has long been known that there is a special affinity of psoriasis for the scalp: Here, it occurs most frequently, lesions terminate sharply in frontal skin beyond the hair line and are difficult to treat. Yet, surprisingly, scalp psoriasis only rarely causes alopecia, even though the pilosebaceous unit clearly is affected. Here, we systematically explore the peculiar, insufficiently investigated connection between psoriasis and growing (anagen) terminal scalp hair follicles (HFs), with emphasis on shared regulatory mechanism and therapeutic targets. Interestingly, several drugs and stressors that can trigger/aggravate psoriasis can inhibit hair growth (e.g. beta-blockers, chloroquine, carbamazepine, interferon-alpha, perceived stress). Instead, several anti-psoriatic agents can stimulate hair growth (e.g. cyclosporine, glucocorticoids, dithranol, UV irradiation), while skin/HF trauma (Köbner phenomenon/depilation) favours the development of psoriatic lesions and induces anagen in "quiescent" (telogen) HFs. On this basis, we propose two interconnected working models: (a) the existence of a bidirectional "hair follicle-psoriasis axis," along which keratinocytes of anagen scalp HFs secrete signals that favour the development and maintenance of psoriatic scalp lesions and respond to signals from these lesions, and (b) that anagen induction and psoriatic lesions share molecular "switch-on" mechanisms, which invite pharmacological targeting, once identified. Therefore, we advocate a novel, cross-fertilizing and integrative approach to psoriasis and hair research that systematically characterizes the "HF-psoriasis axis," focused on identification and therapeutic targeting of selected, shared signalling pathways in the future management of both, psoriasis and hair growth disorders.

Effect of hair removal on solar UV transmission into skin and implications for melanoma skin cancer development

Melanoma is the severest type of skin cancer. As distinct from many other cancer types, the incidence of melanoma has been increasing steadily over the last century. Discovering new risk factors of melanoma will not only raise public awareness but also potentially contribute to the improvement of skin cancer protection in the future. Nowadays, the tendency of shaving skin hair is becoming increasingly popular for aesthetic purposes. However, human hair serves several functions, one of which is ultraviolet (UV) protection for the skin. What is more, stem cells found in the follicles of hair could be the origin of melanoma upon exposure to ultraviolet radiation. Therefore, it is of interest to investigate the effect of shaving on solar UV transmission in the skin. To achieve that, two groups of skin models are constructed in TracePro software: one with unaltered hair and one with shaved hair. The UV transport in the models is simulated using the Monte Carlo method and the absorptions in the stem cells layer are compared. It is found that shaving will increase the UV transmission to the follicular stem cells to a certain degree. More specifically, shaving limbs will generally increase the solar UV transmission from about 5% to 20% in the UV wavelength range.

Morphometric characteristics of feminine eyebrows: variations with ethnicities and age

OBJECTIVE

To explore some morphological features of the eyebrows of women of different ethnicities and ages.

MATERIALS AND METHODS

Standard digital photographs of 3600 women of six ethnicities, aged 18-84 years, previously used to describe the morphology of the human eyes, allowed us to focus on their eyebrows, as supplementary and opportunistic study. Photographs of both eyebrows were analysed partly by manual markings and automatically by dedicated algorithms. Six parameters of the eyebrows were recorded: length, waviness/curvature, oblique aspect, size (vertical height), total surface and hair coverage (density).

RESULTS

Most criteria present ethnic specificities. These are: length (longer eyebrows of Indian, shorter among African women); waviness where the straighter eyebrows were found among Chinese and Japanese women. In general, the longer the eyebrows, the higher their waviness and vice versa. Thickness (or height) of the eyebrows presents a wide ethnic variability as well as hair coverage, where African women present the lower hair density, inversely to Indian women. The same holds true with regard to the total surface of eyebrows, of a large variability (by about four times). Some criteria appear more individually dependent than ethnic-specific, such as the oblique positioning, at the exception of Indian women with less oblique eyebrows. In all subjects, the criteria of both eyebrows (Left vs. Right) were found to be highly correlated (r > 0.7, P < 0.001).

CONCLUSION

The present investigation brings new findings on a scarcely studied facial element, the morphologic features of which are, for most, ethnic-dependent. As applied consequences, the results of the present work pave the road to better adapt adorning procedures of the eyebrows vis-à-vis ethnic and age specificities.