The sun, a powerful source of energy, also emits ultraviolet (UV) radiation that can have both positive and negative effects on our skin. While sunlight is essential for vitamin D synthesis and overall well-being, prolonged or excessive exposure to UV rays can lead to various skin-related issues. Let’s delve into the effects of UV radiation on the skin and explore the mode of action of UV filters.
UV spectrum of light causes sunburn, skin aging, production of precancerous and cancerous lesions, and immunosuppression. Sunburn is caused by UVB rays and results in characteristic erythema. This is due local inflammation state and vasodilation of cutaneous blood vessels. Premature aging is caused mainly by UVA rays, which have longer wavelengths than UVB and penetrate deeper into the dermis. The biological effect is collagen and elastin damage. Visual effects are tan (short run), fine lines, and wrinkles (long run). UVA radiation also prompts the thickening of the outermost layer of the skin. Excessive UV light can also lead to hyperpigmentation, which occurs when the skin produces excess melanin. Hyperpigmentation can be divided into age spots, melasma, and post-inflammatory hyperpigmentation. UV radiation is a proven human carcinogen, causing squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). Both of these cancer types often occur on sun-exposed areas of the skin. Fortunately, if detected and treated early, they are usually curable.
Let’s not forget that UV radiation also has beneficial effects, like participation in the production of vitamin D. However, to prevent the negative effects mentioned above, skin can be protected by regular use of sunscreens, sun-protection clothing, and glasses with UV filters. Avoiding sun on days with high UV index is also recommended. Periodic skin examinations by a dermatologist help detect any potential signs of skin damage or abnormalities, including early stages of skin cancer.
UV filters are chemical compounds that impede the UV radiation passage. In plain language, they act as a shield. Sunscreens are multi-component products that contain at least one UV filter, but the most common are mixtures of UV filters. UV filters can be divided into UVA (further divided into UVA1 and UVA2), UVB, or broad spectrum (UVA+UVB) due to portions of the UV spectrum in which they have maximal absorption peaks. Another classification is organic (chemical) and inorganic (physical). It was believed before that chemical filters only absorb radiation while physical filters only reflect or scatter. The current state of knowledge ensures that both types can absorb, reflect, and scatter the light, however, the percentage share of these phenomena is different in both groups.
The most important structure element of most organic sunscreens is a chromophore which enables electron transitions. Chromophores contain aromatic carbon and/or other electron-dense bonds that are responsible for absorbing UV light. Next, energy from UV radiation excites electrons in the UV filters, and this energy is released as a negligible amount of heat not affecting the skin. When the UV filter is photostable, an electron will return to its ground state and the process can be repeated. As UV filters vary in photostability, some may undergo breakdown or photodegradation when exposed to prolonged or intense UV radiation. This breakdown could reduce the effectiveness of the sunscreen over time, emphasizing the importance of reapplying sunscreen.
Understanding the reactions between UV filters and UV light is crucial for formulating effective sunscreens that provide reliable protection. Sunscreen manufacturers carefully select and combine UV filters to ensure broad-spectrum coverage and photostability, contributing to the overall safety and efficacy of sun protection products. Understanding the effects of UV radiation on the skin empowers individuals to make informed choices about sun exposure. While sunlight is essential for various physiological processes, responsible and cautious sun practices, coupled with protective measures, are essential for maintaining healthy and radiant skin throughout life.
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