Table 1.

Cutaneous stressors, skin damage and protection technologies.

Environmental Aggressor	Solar Radiation		Pollution
	UVA/UVB	VL and IR	Tropospheric Ozone (O3)	Particulate Matter	Transition Metals	Cigarette Smoke
Biomarkers of Exposure and Damage	UVB (290–320 nm) [5,8] Skin erythema DNA mutations (CPDs) UVA (320–400 nm) [11,12,17,18] Dermal matrix protein degradation ✓ Reduction in collagen and elastin via upregulation of MMPs ✓ Reduction in collagen production via downregulation of TGFβ pathway Release of labile iron (Fe(II)-ion) Suppression of cutaneous APC Photodamage	VL (400–700 mm) [23,24,25,26,27,28,29] Includes high energy blue light (400–500 nm) Erythema in darker skin types Immediate and long-lasting pigmentation in darker skin types Increase MMPs Increase inflammatory cytokines IR (760 nm–1 mm) [30,31,32,33,34,35,36] Generates heat energy and increases skin temperature Erythema ab igne Increase MMPs Accumulation of elastotic material Induces angiogenesis ROS within mitochondria Modulates fibroblast activity	Interacts with stratum corneum lipids, proteins, and DNA Increases ROS HO−, O2−, and H2O2 [40,50,51,52] 4-HNE adducts form and induce further lipid peroxidation Activation of NF-кβ aryl hydrocarbon receptor Ahr and HSPs enhance release of IL-8, COX2 (ozone-induced inflammation) [40,48,53,54,55,56,57] Increases in MMP-2 and MMP-9 (ozone-induced aging) and skin cancer progression, respectively [58]	Particulate matter (PM) Includes poly-aromatic hydrocarbons (PAHs), metals, inorganic and organic toxins Combines with oxidized nitrogen oxides, sulfur and volatile organic compounds and UV light to form photochemical smog Decreases stratospheric O3 Increases ground level O3 Absorbed through inhalation, skin and hair 4-HNE from lipid peroxidation can damage DNA and mitochondria Stimulates key oxidative and inflammatory transcription factors NF-кβ, AP-1, NRF2, Ahr [5,63,64,65,66] Increase in skin barrier disruption, inflammatory and skin diseases (COPD, asthma, acne, atopic dermatitis, skin aging) [59,60,61,62]	PM in combination with UV can liberate bound iron in the skin as labile iron Interacts with ROS to cause oxidative stress and damage to mitochondria, lipids, DNA, and cellular proteins [91,92,93,94,95] Increase lipid peroxidation Increase MMP-9 Decrease filaggrin and involucrin [102,103,104] Disruption of skin barrier [106,107,108]	Increase ROS Secondary lipid peroxidation Increase release of inflammatory cytokines IL-1α, IL-6. TNF-α Increase MMP-1 Increase collagen degradation Increase cutaneous inflammation and skin diseases [40,78,79,80,81] Increase NRF2 and MMP-9 Decrease skin barrier and wound-healing [82]
Protection	Physical Barriers- Sun shirts Hats Sunglasses Sunscreens- Broad spectrum chemical Mineral TopicalAOX- [151,152,153,165,166,167,168] Vitamins C, E Ferulic acid Resveratrol Carotenoids Epigallocatechin gallate (EGCG) Co-enzyme Q10 Caffeic acid Lycopene Other botanicals Chelators [190,191] 2-furildioxime Kojic acid DNA Repair Enzymes with sunscreen and/or AOX [203,204,205,206,207,208] Diet, Micronutrients [131]	Physical Barriers- Sun shirts Hats Sunglasses Sunscreens and Cosmetics- Tinted containing iron oxide (FeO) for VL [129] Topical AOXs for IRA- [176,177] Vitamins C, E Ferulic acid Resveratrol Co-enzyme Q10 Grape seed extract Sunscreen with AOX blend for VL [178] Diet and Micronutrients [131]	Topical AOX- [42,146,147] Vitamins C, E Ferulic acid Other botanicals Diet and Micronutrients [131]	Topical AOX- [42] Vitamins C, E Ferulic acid Other botanicals Diet and Micronutrients [131]	Combination- [89] Chelators PLUS topical AOX Diet and Micronutrients [131]	Topical AOX- [148] Resveratrol Diet and Micronutrients [131]