Aging is an inevitable and normal biological process in humans. Like all human organs, your skin ages and, as you get older, starts exhibiting telltale signs of biological aging (senescence): wrinkles, sagging, and loss of moisture and fat. While numerous factors such as genetics and lifestyle can accelerate the process, research has helped identify aging mechanisms that can be targeted to slow down or delay the appearance of visible signs of aging on skin. Consequently, the multibillion-dollar beauty industry offers a vast array of products and procedures that promise a more youthful complexion, with a growing emphasis on natural compounds.
Recently, the microbiome of the skin and possible interventions to modulate skin aging has presented a new area of investigation. While skin-aging research prioritizes changes in wound healing and protection against disease and infection, this article encompasses the research addressing the role of the microbiome and possible benefits of probiotics against skin aging.
Skin aging, in brief
The skin undergoes a complex aging process, caused by both intrinsic (genetic, hormonal, and cellular metabolic changes) and extrinsic factors which include environmental influences (pollution, sun exposure, and climate) as well as lifestyle elements (cigarette smoking, diet, exercise, stress, sleep, chemical exposure, trauma, and air pollution).
As skin ages, lipid composition, sebum secretion, and pH change. These affect skin dryness, collagen fragmentation, and reduction in the total amount of collagen and elastin, as well as influencing the skin ecology, possibly shaping the skin microbiome.
A foremost driver of skin aging stems from the weakening of the antioxidant system. Damage from reactive oxygen species secondary to normal aerobic metabolism, and exogenous factors, such as ultraviolet radiation (primarily sun exposure) leads to cellular senescence or apoptosis (cell death). Oxidative insult also appears to provoke telomere shortening, which leads to cellular senescence.
The critical role that senescent cells play in the development of skin aging phenotypes is well documented. Senescent cells accumulate in skin tissue with age and can spread senescence to surrounding healthy cells, possibly initiating a systemic impact.
Microbiome and skin aging
Similar to the gut microbiome, the skin microbiota is composed of many billions of microorganisms, including bacteria, fungi, and viruses. Though composition and levels of diversity may be different than that in the gut, the microbes in the skin also safeguard against the environment and pathogens. Recent research indicates that both bacterial diversity and the relative abundance of different microbes present on and in the skin may contribute to skin barrier stability or dysfunction.
The skin microbiota composition is influenced by many factors. Different parts of the skin host a variety of microbes depending on characteristics such as moisture and sebum levels. Other factors may change the microbial picture. People living in rural areas harbor different microbes than those living in urban areas. But when people live together, their skin microbes start looking alike. In addition, the use of makeup has been shown to greatly increased community diversity on the forehead skin whereas topical antibiotics have induced a decrease in the commensal Staphylococcus spp. population, which is known to compete for colonization with pathogenic Staphylococcus aureus.
Though an optimum skin microbiota is not known, evidence suggests age-related microbial changes in the skin, with a recent study revealing differing microbial signatures found in cheek microbiomes of older versus younger Chinese women. Proteobacteria and Actinobacteria phyla were more abundant on the older skin, whereas younger individuals showed a higher prevalence of Bacteroidetes and Firmicutes phyla. The younger skin also showed higher alpha diversity, a measure of species richness. Moreover, a difference in trans-epidermal water loss and sebum production was found between the two groups, which are indicators of skin aging. Other studies also found skin microbial shifts with aging.
Skin microbes secrete enzymes involved in skin homeostasis; other roles include quorum sensing, production of biofilms and bacteriocins, pH regulation by sebum and free fatty acid production, and modulation of innate and adaptive immune responses. Moreover, the skin microbiota plays an important role in protecting against potentially pathogenic microorganisms through competition and antimicrobial peptide production by commensal bacteria.
However, microbial dysbiosis at aging skin sites interferes with these processes. An imbalance not only disrupts normal functioning locally but also exerts systemic effects via the gut-skin axis (the bidirectional communication pathway between the gut microbiome and the skin). An impaired epidermal barrier resulting from aged skin can contribute to systemic low-grade chronic inflammation (inflammaging), which is also highly associated with age-related alterations to the gut microbiome. Conversely, intestinal dysbiosis may result in increased epithelial permeability, which may lead to an accumulation of bacterial metabolites in the skin, as well as impairment in epidermal differentiation and skin integrity. Furthermore, pro-inflammatory cytokines are triggered, setting up a vicious cycle of chronic systemic inflammation.
Probiotics and skin aging
Microbiota-targeted probiotic interventions have been shown to favorably affect the host’s health and aging by an enhancement of antioxidant activity, improvement of immune homeostasis, suppression of chronic inflammation, regulation of fat deposition and metabolism, and prevention of insulin resistance.
Specific to skin aging, studies demonstrate that probiotics can restore acidic skin pH, alleviate oxidative stress, attenuate photoaging, and improve skin barrier function.
While there are many studies, the following offer two examples:
- In a study in mice, a Levilactobacillus brevis strain attenuated UV-induced barrier perturbation and oxidative stress of the skin. The effect was attributed to the prevention of ROS generation.
- A strain ofLactiplantibacillus plantarum decreased the symptoms of UV-induced skin photo-aging in humans. A trial in 110 participants aged 41–59 years found that daily intake for 12 weeks could significantly improve skin hydration, skin gloss, skin elasticity, and alleviate facial wrinkles compared with the placebo group.
Scientific evidence suggests that both the skin and gut microbiomes are intricately involved with skin aging via the gut-skin axis. Promising research on this topic shows that probiotics could beneficially modulate the microbial composition of the skin microbiome and attenuate skin aging. Some of the proposed mechanisms for such effects involve restoring acidic skin pH, alleviating oxidative stress, attenuating photoaging, and improving skin barrier function. More clinical studies are needed.
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