The skin microbiome remains a fascinating realm that continues to elude complete understanding. With each passing year, we unravel its mysteries and uncover new insights. Researchers are fervently exploring the potential of manipulating the skin microbiome to treat various skin disorders, both externally through cosmetic products enriched with pre- and probiotics, as well as internally. Disruptions in this intricate ecosystem can also impact our hydrolipidic mantle, seen in conditions like rosacea or seborrheic dermatitis. Specifically, lipophilic fungi belonging to the Pityrosporum Ovale genus lack the ability to synthesise their own fatty acids. Consequently, they secrete hydrolytic enzymes, such as lipases and phospholipases, which alter the composition of our skin surface lipids.
Interestingly, even the manner in which we enter this world plays a role in shaping our future skin barrier. We observe distinct variations in the composition of skin microbiota between individuals born naturally and those born via cesarean section. As time progresses, the skin microbiome matures, becoming increasingly diverse and unique, influenced by a multitude of factors. Variations in microbiome compositions can be observed in regions abundant in sebaceous glands, like the face, as well as in moist areas with a high density of sweat glands, and dry regions such as the forearms. It is reasonable to assume that a significant correlation exists between the microorganisms residing on our skin and the composition of our skin surface lipids. Given the multitude of factors at play in regulating our skin microbiota, it is a highly individual and distinctive entity, much akin to a fingerprint.
AGING OF THE SKIN BARRIER
The aging process affects both the internal and external components of our skin barrier, making it less resistant. Looking at the diagram above, we can observe the changes that occur over time. One noticeable change is the decrease in the number of lamellar bodies, which leads to a reduced production of epidermal lipids. As a result, the cellular cement weakens, causing an increase in transepidermal water loss (TEWL) and making the barrier more permeable to harmful substances. Additionally, the sebaceous glands produce less sebum, further compromising the barrier's integrity.
It is not only the lipids that are affected in this process, but also other essential components. The production of filaggrin, for instance, decreases, leading to a decrease in the production of its breakdown products called natural moisturising factor (NMF). This has serious consequences for the skin's hydration and overall health. Furthermore, the graph depicts a decrease in the expression of the membrane protein AQP3, which plays a crucial role in transporting glycerol and water between skin cells. AQP3 also contributes to lipid synthesis.
Overall, the aging process significantly impacts the skin barrier, making it less effective in its protective functions. The decrease in lipids, filaggrin, and AQP3 expression all contribute to the weakening of the barrier, leaving the skin more vulnerable to damage from external factors and reducing its ability to retain moisture.
ANTIBACTERIAL FUNCTION OF THE HYDROLIPID FILM.
The hydrolipid mantle is our first barrier in the fight against the external environment. Free sphingoid bases, which are the product of enzymatic hydrolysis of epidermal ceramides, demonstrate broad activity against pathogenic microorganisms. One of the components of sebum - sapienic acid, belonging to fatty acids, also exhibits similar activity. The acidic pH alone creates unfavourable conditions for the multiplication of pathogenic pathogens. When it comes to the shield against microorganisms, let us not forget about AMPs, which are Antimicrobial Peptides, including beta-defensin and cathelicidin, as well as the well-known lactoferrin.
SUMMARY
In recent research, the significance of lipids in the hydrolipid film of the skin has become evident. These lipids serve various crucial functions, although their complete understanding is still under investigation. They play a pivotal role in protecting the skin from the harmful effects of free radicals and UV radiation. Additionally, they provide defence against pathogens and reduce transepidermal water loss (TEWL). Moreover, lipids facilitate communication between the skin and the external environment, as well as between different skin cells. They also influence the skin microbiota.
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