The Spectral Erythemic Reaction of the Human Skin to Ultra-Violet Radiation
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Get free access to newly published articles. Create a personal account to register for email alerts with links to free full-text articles. Sign in to save your search Sign in to your personal account. Create a free personal account to access your subscriptions, sign up for alerts, and more. Purchase access Subscribe now. In vivo and in vitro studies do not show the penetration of titanium dioxide but, in relation to zinc oxide, research has indicated limited penetration into the skin.
Micronized forms of titanium dioxide and zinc oxide can undergo photochemical reactions that jeopardize their effectiveness, causing damage to genetic material or changing cell homeostasis.
B L Diffey
The coating of particles with dimethicone or silica promotes their stability, reducing such drawbacks. New developments have recently surfaced to raise the quality of inorganic photoprotectors; for example, their encapsulation with carnauba wax. Carnauba wax contains cinnamates which, together with titanium dioxide, generate stable dispersion with proper viscosity and a significant increase in both the SPF value and UVA protection. Organic filters are molecules capable of absorbing UV radiation and transforming it into energy that is harmless to humans.
Graphs 1 and 2 show the absorption spectrum of two organic filters. They are essentially aromatic compounds combined with carboxylic groups which often have an electron donor group such as, for instance, an amine or methoxyl in the ortho or para position of the aromatic ring. As for solubility, they may be water or fat soluble. These molecules, upon returning to their ground states, release excess energy absorbed in the form of heat, for example. However, UVA and broad-spectrum filters are the result of recent research.
Many products currently use a different combination of filters to obtain broad-spectrum protection. The effectiveness of organic filters is directly related to photochemical stability, easier and permanent dispersion and dissolution, and to water-resistance. These filters must be nontoxic and must not cause irritation or allergy. Reactions with other p -molecules may occur and there is the possibility of carcinogenesis related to the use of products containing PABA.
The first PABA-free products were developed in the 80s. PABA esters were marketed, which had advantages such as reduced reactivity and allergenicity. The only FDA-approved ester is Padimate O or octyl dimethyl PABA 2-ethylhexyl 4-dimethylaminobenzoate , most currently used in products to protect the hair and in combination with other filters to increase the SPF of sunscreens. They have lower potential to cause skin irritability. Studies show that its nanoencapsulation with poly-D, L-lactide-co-glycolide results in decreased photodegradation.
Salicylates are stable and safe aromatic compounds, water-insoluble, which have high substantivity.
This group of compounds has been used as sunscreen for decades and also as solvents for poorly soluble sunscreens, such as benzophenones. We may cite 2-ethylhexyl salicylate, homomenthyl salicylate and triethanolamine salicylate. This does not occur with homomenthyl salicylate. Salicylates offer UVB protection in the range of nm. Triethanolamine salicylate is more often used in products for hair protection. The main organic UVA filters in sunscreens include benzophenones mainly oxybenzone , avobenzone, terephthalylidene dicamphor sulfonic acid, drometrizole trisiloxane, methylene-bis-benzotriazolyl tetramethylbutylphenol and bis-ethylhexyloxyphenol methoxyphenyl triazine.
According to Baron et al, the FDA recently approved the use of terephthalylidene dicamphor sulfonic acid; however, methylene-bis-benzotriazolyl tetramethylbutylphenol and bis-ethylhexyloxyphenol methoxyphenyl triazine have not yet been approved by this agency. Menthyl anthranilate is classified as an UVA filter, but it is rarely used. Benzophenones are aromatic ketones, and the FDA approved the use of oxybenzone benzophenone-3 in the early 80ss.
Benzophenones, as a class, are considered allergenic sunscreens. They have low substantivity and the incidence of contact and photocontact dermatitis is high. Avobenzone was introduced in the late 80s and early 90s. It was the first to provide UVA-I protection, covering the wavelength range of to nm. Avonbenzone suffers significant degradation as a result of exposure to light.
A sunscreen with good UVB protection is generally added, such as homoment range of to nm. A sunscreen with good UVB protection is generally added, such as homomenthyl salicylate. Recent research aims at developing new vehicles for avonbenzone containing more effective stabilizers. Industries invest in the development of final formulations, involving, for example, combinations of avobenzone with octocrylene 2-cyano-3, 2-ethylhexyl 3-diphenylacrylate.
The addition of bis-ethylhexyloxyphenol methoxyphenyl triazine photostabilizes avobenzone. Terephthalylidene dicamphor sulfonic acid was approved by the FDA in It is a photostable organic filter that absorbs the wavelength range between and nm, with maximum absorption peak at nm. When it is combined with avobenzone, UVA protection is increased. In vivo studies have shown protection against photoaging and the development of photodermatoses. Another organic filter recently introduced in the market is drometrizole trisiloxane. In , this filter was introduced in Canada; however, it has not been approved by the FDA.
Methylene-bis-benzotriazolyl tetramethylbutylphenol and bis-ethylhexyloxyphenol methoxyphenyl triazine are organic filters of broad-spectrum not yet approved by the FDA. Bis-ethylhexyloxyphenol methoxyphenyl triazine increases the photostability of avobenzone and both methylene-bis-benzotriazolyl tetramethylbutylphenol and bis-ethylhexyloxyphenol methoxyphenyl triazine act as active compounds in the prevention of photoaging.
The natural consumption of oxygen by aerobic beings generates oxidative processes. Under normal conditions, the human body is able to neutralize, by means of antioxidant systems, reactive oxygen species ROS generated physiologically, but in pathological conditions or under the effects of chronic and excessive exposure to UV radiation, an imbalance between the production of ROS and antioxidant systems is established.
Ultraviolet radiation (EHC 14, )
Therefore, there is an oxidative stress capable of causing skin cell damage, such as lipid peroxidation, protein denaturation and DNA changes. The damage caused may result in immunosuppression, premature skin aging and skin cancer development Antioxidants are defined as substances which, when present in low concentrations as compared with those of an oxidizable substrate, significantly reduce or prevent the oxidation of this substrate.
They may act by preventing the formation of free radicals, repairing the damage caused by them or sequestering them. Many cosmetic products on the market have built-in antioxidants to fight the signs of aging skin. Several studies currently investigate the action of antioxidants in photoprotection.
Some studies evaluate their action in the prevention of skin erythema by determining FPS value and others evaluate their protective effects against molecular damage caused by oxidative stress induced by UV radiation. Polyphenols are natural components of plants that are found in fruit, vegetables, seeds, bark and flowers. They have antioxidant, anti-inflammatory and immunomodulatory properties.
They are explored as chemopreventive agents in various skin diseases, including skin cancer. Studies have shown the effectiveness of natural polyphenols against inflammation, oxidative stress, DNA damage and suppression of the immune response induced by UV radiation. These protective effects contribute to their anti-photocarcinogenic action.
Sunscreens have several health benefits, but there are controversies and challenges associated with the efficacy and safety of their use 3. According to Gonzalez et al, , the exposure of the population to organic filters increased after they were added to various cosmetic products. A study of Australian volunteers showed that Allergic reactions to sunscreens were not found. Allergic reactions to sunscreens and allergic contact and photocontact dermatitis are rare. Contact photoallergy usually occurs due to the presence of benzophenone-3 oxybenzone , the major responsible for its development.
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PABA, amyl dimethyl PABA and benzophenone, well-known photoallergenic agents, are no longer used, contributing thus to reduce cases of skin irritation caused by the continuous use of sunscreens. Systemic absorption. UV filters, such as benzophenones and 2ethylhexyl 4-methoxycinnamate, can be detected in plasma and urine of individuals who used them topically. However, most studies related to this were conducted with formulations having a high concentration of these substances, differently from the concentration found in commercially available products. Resolution 47 of lists the sunscreens that have been approved for use and their maximum concentration.
Therefore, research on the systemic absorption of sunscreens must be conducted with formulations having the maximum concentration of sunscreens allowed by responsible agencies. Factors involved in the systemic absorption and chronic toxicity of UV filters have been intensely debated, but it is necessary to investigate the commercially available sunscreens to assess the degree of absorption of UV filters and the consequences of this absorption.
Synthesis of Vitamin D Calciferol. Ultraviolet radiation is necessary for the synthesis of vitamin D calciferol.
The consistency of studies of ultraviolet erythema in normal human skin
This synthesis occurs in the presence of UVB radiation. Photoprotectors are often effective in their UVB protection. Few studies associating the role of vitamin D, sun exposure and cancer prevention have been conducted, so research in this area is necessary. It is also important to investigate oral vitamin D and its synthesis after sun exposure. Studies about the optimal amount of vitamin D needed for its beneficial effects are also important. This recommendation was based on evidence suggesting that vitamin D could reduce the risks of breast, prostate and colorectal cancer.
Physicians should individualize sun protection, evaluating whether or not oral supplementation of vitamin D is necessary in each case and also the degree of photoprotection indicated for each patient. Currently, there is increasing use of nanomaterials in electronic components, antifungal and antimicrobial preparations, cosmetics, among others. Nanoparticles are unique particles with a diameter inferior to nm that represent a subset of nanomaterials; their clusters can have sizes greater than nm.
Insoluble nanoparticles with diameters between 50 and nm, mainly represented by titanium dioxide TiO 2 and zinc oxide ZnO are used in photoprotectors. The reflection of UV radiation by TiO 2 is more efficient in particles sized between 60 and nm. ZnO is commonly used in particles sized between 30 and nm. The use of nanoparticles in photoprotectors improved the whitish appearance of traditional photoprotectors and created a more transparent vehicle, less viscous and with better spreadability on the skin.
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This improved its acceptability by consumers. The potential toxicity of nanoparticles in photoprotectors is the result of their size, the ability to escape immune defense mechanisms, the ability to form protein complexes, and most importantly, the ability to induce the formation of free radicals.
Some review studies suggest a potential of penetration of nanoparticles topically applied to human skin causing systemic risk to health. They also suggest that nanoparticles can penetrate the skin and be distributed throughout the body by the circulatory system.
The penetration of materials in the stratum corneum is limited by molecular size. The intercellu-lar space between cells of the stratum corneum is approximately nm3 and it can be extended with the topical application of various products. This fact instigates debates about the penetration of nanoparticles into the stratum corneum. A study conducted by Philip et al, , assessed the location and the possibility of penetration of nanoparticles dispersed in three photoprotectors, into normal and altered skin.
They found that levels of TiO 2 and ZnO nanoparticles were nonexistent or very low to be detected in the layers of viable epidermis below the stratum corneum. This result cannot be extended to other photoprotectors, since different formulations may have different properties.
Further studies should be conducted to determine the safety of TiO 2 and ZnO nanoparticles in sunscreens. In addition to the evaluation of skin penetration, assays of the generation of reactive oxygen species as a result of exposure of nanoparticles to UV radiation and the consequent penetration of ROS generated in the stratum corneum should be conducted. The need for photoprotection is an irrefutable reality, whether for therapeutic and prophylactic action against premature aging or to decrease the incidence of skin cancer. Over the years, we have seen improvements in the development of photoprotectors to obtain safe and effective formulations which provide broad UV protection.
Research studies related to the development of new molecules, less allergenic and with better photostabilization, are needed to obtain ideal photoprotectors. In-depth studies of the safety, efficacy and systemic absorption of photoprotectors are important for the total understanding of the interactions involved in their use, which is essential and indispensable considering the damage caused by UV radiation. Update on photoprotection.