![]() That is why the safety of cosmetic products containing NPs, in particular the sunscreens, has been frequently discussed. 11 Since the surface area to volume ratio of particles increases as the particle diameter decreases, nanoparticles (NPs), ie, nanoobjects with all three external dimensions in the nanoscale, 12 may be more (bio)reactive than normal bulk materials. 10 The natural opaqueness of these microsized sunscreen components is eliminated without reducing their UV blocking efficacy by utilizing nanosized ZnO and TiO 2 particles. 9 Advantages offered by sunscreens based on inorganic compounds comprise absence of skin irritation and sensitization, inertness of the ingredients, limited skin penetration, and a broad spectrum protection. They are preferred above organic compounds that solely absorb UV radiation. Minerals like zinc oxide (ZnO) and titanium dioxide (TiO 2) are frequently used as inorganic physical sun blockers. 8 In the last decennia, only sunscreens containing both UVB and UVA filters, are being produced. Sunscreens should provide protection against the adverse effects of both UVB and UVA radiation. The scientific evidence that sunscreens protect against the other two common types of skin cancer, basal cell carcinoma and malignant melanoma is inconclusive. 3, 4 Although many patients (and their doctors) believe that a regular use of sunscreens provides protection against the development of skin cancer, this protective effect has only been confirmed in the case of actinic keratoses and squamous cell carcinoma. The loss of the skin elasticity is being ascribed especially to U VA producing reactive oxygen species (ROS) that activate different matrix metalloproteinases, which damage collagen and other dermal matrix proteins. The dermal part of the skin plays an important part in the photoaging process. The formation of actinic keratoses and skin cancer from epidermal cells are known examples. Long-term effects of sunlight include different degenerative skin changes. They include cholecalcipherol (vitamin D) synthesis and, at higher UVB doses, the possibility of developing skin redness (erythema). Short-term reactions to sunlight can be largely ascribed to UVB radiation. But most of the remaining UVB together with UVA (UVA-2, 320–340 nm and UVA-1, 340–400 nm) rays reach our skin and cause biological and metabolic reactions. This stratospheric ozone can partly absorb UVB (290–320 nm) rays. Part of this radiation, UVC (100–290 nm), is filtered off from the atmosphere mainly because wavelengths smaller than 242 nm are absorbed by stratospheric molecular oxygen to produce ozone. ![]() Sunscreens are used to protect the skin against the harmful effects of solar ultraviolet (UV) radiation. Caution should still be exercised when new sunscreens are developed and research that includes sunscreen NP stabilization, chronic exposures, and reduction of NPs’ free-radical production should receive full attention. Photocatalytic effects, the highest for anatase TiO 2, cannot be completely prevented by coating of the particles, but silica-based coatings are most effective. Both sunscreen NPs induce (photo)cyto- and genotoxicity and have been sporadically observed in viable skin layers especially in case of long-term exposures and ZnO. Skin exposure to NP-containing sunscreens leads to incorporation of TiO 2 and ZnO NPs in the stratum corneum, which can alter specific NP attenuation properties due to particle–particle, particle–skin, and skin–particle–light physicochemical interactions. ![]() Utilization of mixtures of micro- and nanosized ZnO dispersions and nanosized TiO 2 particles may improve this situation. With the use of TiO 2 and ZnO NPs, the undesired opaqueness disappears but the required balance between UVA and UVB protection can be altered. This review focuses on significant effects on the UV attenuation of sunscreens when microsized TiO 2 and ZnO particles are replaced by NPs and evaluates physicochemical aspects that affect effectiveness and safety of NP sunscreens. However, to solve the cosmetic drawback of these opaque sunscreens, microsized TiO 2 and ZnO have been increasingly replaced by TiO 2 and ZnO nanoparticles (NPs) (<100 nm). As TiO 2 is more effective in UVB and ZnO in the UVA range, the combination of these particles assures a broad-band UV protection. Titanium dioxide (TiO 2) and zinc oxide (ZnO) minerals are frequently employed in sunscreens as inorganic physical sun blockers. According to the United States Food and Drug Administration, the protection factor against UVA should be at least one-third of the overall sun protection factor. Sunscreens are used to provide protection against adverse effects of ultraviolet (UV)B (290–320 nm) and UVA (320–400 nm) radiation.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |