Fragility of epidermis in newborns, children and adolescents.

Within their first days of life, newborns' skin undergoes various adaptation processes needed to accommodate the transition from the wet uterine environment to the dry atmosphere. The skin of newborns and infants is considered as a physiological fragile skin, a skin with lower resistance to aggressions. Fragile skin is divided into four categories up to its origin: physiological fragile skin (age, location), pathological fragile skin (acute and chronic), circumstantial fragile skin (due to environmental extrinsic factors or intrinsic factors such as stress) and iatrogenic fragile skin. Extensive research of the past 10 years have proven evidence that at birth albeit showing a nearly perfect appearance, newborn skin is structurally and functionally immature compared to adult skin undergoing a physiological maturation process after birth at least throughout the first year of life. This article is an overview of all known data about fragility of epidermis in 'fragile populations': newborns, children and adolescents. It includes the recent pathological, pathophysiological and clinical data about fragility of epidermis in various dermatological diseases, such as atopic dermatitis, acne, rosacea, contact dermatitis, irritative dermatitis and focus on UV protection.

Characterization of a human epidermis model reconstructed from hair follicle keratinocytes and comparison with two commercially models and native skin.

OBJECTIVE: Outer root sheath (ORS) cells of human hair follicles are a readily available, non-invasive source of keratinocytes for epidermis reconstruction. The aim of this study was to characterize a model of epidermis reconstructed from ORS cells (ORS-derived model) and to evaluate its reproducibility, in comparison with native human skin and two marketed reconstructed skin models (model A, Episkin(®) and model B, Skinethic(®) ). METHODS: Cell morphology and tissue architecture of the three models were analysed histologically and proliferation and differentiation marker expression by immunohistochemistry and mRNA quantification. RESULTS: All models displayed the same general epidermal architecture as native epidermis, but with a thicker stratum corneum in models A and B. Compared with native epidermis, Ki67 was correctly localized in epidermal basal cells in all models, as K10 in suprabasal layers. In all skin models, transglutaminase 1 (TGM1) was prematurely expressed in suprabasal layers. However, this expression was only observed from the upper stratum spinosum in the ORS-derived model. In this model, filaggrin and loricrin were correctly located in the stratum granulosum. Filaggrin, involucrin, loricrin and TGM1 mRNAs (markers of keratinocyte terminal differentiation) were transcriptionally expressed in all models. In the ORS-derived model, transcriptional expression level was similar to that of native skin. CONCLUSION: ORS cell-based reconstructed epidermis is a valid and reproducible model for human epidermis and it may be used to evaluate the effects of active substances and cosmetic formulations.

In vitro approaches to pharmacological screening in the field of atopic dermatitis.

In vitro models are valuable for evaluating potential active ingredients and other molecules used in medications for atopic dermatitis (AD). However, finding appropriate in vitro models can be problematic. Our strategy was to set up different in vitro models that would mimic the pathomechanisms of AD. We describe five such models - the AD keratinocyte model, the AD reconstructed human epidermis model, the adaptive immunity model, the innate immunity model and the pruritus model - which we have used to evaluate a new ingredient for emollients derived from a biological extract. The models chosen provide useful data for the pharmacological characterization of active ingredients in adjunctive treatments for AD.

Fragility of epidermis and its consequence in dermatology.

The skin is the largest organ of the body, providing a protective barrier against bacteria, chemicals and physical insults while maintaining homeostasis in the internal environment. Such a barrier function the skin ensures protection against excessive water loss. The skin's immune defence consists of several facets, including immediate, non-specific mechanisms (innate immunity) and delayed, stimulus-specific responses (adaptive immunity), which contribute to fending off a wide range of potentially invasive microorganisms. This article is an overview of all known data about 'fragile skin'. Fragile skin is defined as skin with lower resistance to aggressions. Fragile skin can be classified into four categories up to its origin: physiological fragile skin (age, location), pathological fragile skin (acute and chronic), circumstantial fragile skin (due to environmental extrinsic factors or intrinsic factors such as stress) and iatrogenic fragile skin. This article includes the epidemiologic data, pathologic description of fragile skin with pathophysiological bases (mechanical and immunological role of skin barrier) and clinical description of fragile skin in atopic dermatitis, in acne, in rosacea, in psoriasis, in contact dermatitis and other dermatologic pathologies. This article includes also clinical cases and differential diagnosis of fragile skin (reactive skin) in face in adult population. In conclusion, fragile skin is very frequent worldwide and its prevalence varies between 25% and 52% in Caucasian, African and Asian population.