Page 87 - Read Online

Page 4 of 16 Mataix et al. Plast Aesthet Res 2020;7:69 I http://dx.doi.org/10.20517/2347-9264.2020.138

these links attract interest because of their potential involvement in the onset and progression of immune
[23]
dysregulation, underpinning conditions such as rosacea or lupus erythematosus .

The solar spectrum comprises different wavelengths, ranging from short, high-energy wavelength radiation
(UVR; < 380 nm) to low-energy infrared radiation (> 800 nm), through the visible spectrum (380-800 nm).
[24]
UVR comprise ~5% of the total radiation spectrum reaching the skin but is the most energetic and is
likely one of the best-studied components of the skin exposome. A major impact of short-wave ionizing
radiation on skin cells is either direct DNA damage by covalent alteration of nucleic acids (mostly exerted
on pyrimidine bases) or indirect damage provoked by reactive oxygen species (ROS) and other highly
reactive products, derived from both generic oxidative stress and the ionizing damage of other cell
structures [5,18] . A relevant principle to mention is the fact that the contribution of ionizing radiations to
skin damage and aging stems from a primary impact on the dermis (including the fibroblasts that serve the
[25]
connective tissue and nurture other components of the dermis and the epidermal layer) .
While lower energy wavelengths have long been regarded as irrelevant, several studies have demonstrated
that radiation across the visible spectrum and even infrared radiations can induce significant responses
in skin cells and tissues (such as pigmentation and expression of stromal remodeling enzymes for tissue
repair such as MMP1), and therefore an impact on their physiology and molecular constituents [5,26-28] .
As their net load is much higher than higher-energy radiations across time, increasing attention is being
devoted to their effect. Wavelengths within the visible blue spectrum are capable of inducing oxidative
stress in vivo, driving significant gene expression reprogramming in skin cells and reducing keratinocyte
proliferation [29-31] . They may also promote a dysregulation of homeostatic molecular systems, such as those
[32]
regulating osmotic balance . This specific wavelength range is currently being intensively studied because
of its higher relative energy and increasing widespread exposure due to electronic devices and artificial
[33]
lighting, also called digital pollution . Infrared light can exert a distinct impact on skin homeostasis and
promotes specific gene expression signatures, including MMP1 upregulation; these effects may partially
derive from its promotion of heat (intrinsically linked to skin aging, see below) apart from direct molecular
mechanisms [5,27,34] .

Miscellanea
Additional environmental factors, such as recurrent exposure to acute temperature changes, can promote
aging, as evidenced by upregulation of different biomarkers indicating tissue damage (inflammatory
infiltration, neovascularization, and oxidative DNA damage) upon exposure to heat [34,35] . Indeed, severe skin
[5]
aging has been observed in exposed body parts in certain occupations such as glass blowers and bakers .
Dryness is also considered a hallmark of skin aging, and molecular changes such as aquaporin expression
are altered with this process. It is thus not surprising that dry climates are associated with increased skin
aging, commonly combining with high solar exposure and extreme temperatures [5,36] .

Modern lifestyle exposes our skin to a remarkable number of agents that can have an impact on skin
health. Cosmetics can deliver different damaging compounds to our skin and are thus regularly screened
not only for intrinsic toxicity but, most importantly, also for their sensitizing effect in the presence of other
agents such as light radiation . An additional class of external agents that can provoke skin damage are
[37]
dietary components that exert metabolic stress, and byproducts of endogenous metabolism are associated
with disturbed patterns of sleep and stress [5,38] . Apart from major imbalances such as insulin resistance
[39]
and diabetes, which are linked to systemic inflammation , high levels of certain nutrients such as
carbohydrates or animal saturated fats and high-protein diets promote adverse metabolic states in otherwise
“healthy” individuals and are linked to tissue aging, including skin aging [5,39-41] . An interesting additional
direct adverse effect of high carbohydrate intake on skin and other tissues has been proposed through the
formation of aberrant protein-glycan adducts, whose deposition may disrupt glycoprotein structures such