紫外線是太陽光中不可見的輻射光。根據波長及其生物效應，可劃分為UVA、UVB和UVC三個主要波段。雖然過度暴露于紫外線會對皮膚造成損害，但適量接觸亦對人體健康具有重要價值。

「紫外線的光譜特性與皮膚影響」

1、UVA（315-400nm）作為長波紫外線，穿透力很強，不僅能直達皮膚真皮層，也可輕易穿透普通玻璃。這意味著即使在室內靠窗位置，皮膚仍會受到UVA輻射。UVA深入真皮層后，會產生活性氧簇等自由基，攻擊并降解膠原蛋白和彈性纖維這些關鍵結構蛋白——膠原蛋白和彈性纖維。長期且反復的UVA暴露，會導致真皮層結構塌陷，表現為皮膚出現深皺紋、松弛、失去彈性。

上一期我們介紹過，針對UVA的防護，我們需要關注防曬產品上的PA標識，PA值越高，防護效果越好。

2、UVB（280-315nm）作為中波紫外線，主要影響表皮層。當皮膚暴露于過量UVB時，表皮細胞會直接受損。身體為應對此損傷，會啟動炎癥反應，皮膚表面形成肉眼可見的紅斑，即曬傷，并增加患皮膚癌的風險。SPF值專門標示對UVB的防護等級，日常使用SPF30即可阻擋約97%的UVB。

3、UVC（200-280nm）雖然能量很強，但絕大多數被大氣層吸收，自然環境中不對人體構成威脅。但需注意，人工UVC光源（如殺菌燈）不可直接照射人體，其短時照射即可灼傷皮膚與眼睛，需嚴格規范使用。

「紫外線的積極作用與生活應用」

適量紫外線對人體健康至關重要。UVB能促進皮膚合成維生素D，這一過程對鈣質吸收和骨骼健康具有不可替代的作用。

UVA憑借其出色的穿透與熒光激發能力，常用于錢及證件防偽鑒定、刑偵取證，其光固化特性也廣泛應用于牙科修復、電子產品涂層和印刷油墨的快速固化。

UVB在醫療領域中，窄譜UVB是治療銀屑病等皮膚病的有效方法；在農業上，可用于提高溫室作物中維生素D的含量。

UVC因其高效的殺菌消毒能力，被廣泛用于飲用水凈化、空氣消毒及醫療器械的無菌處理。

這些應用充分體現了紫外線的“雙面性"：科學利用可造福人類，過度暴露則會造成傷害。我們既不應過度恐懼紫外線，也要避免無防護的長時間暴露。通過合理的防曬措施，在享受戶外生活的同時，盡可能限度降低紫外線對皮膚的傷害，實現人與紫外線的和諧共存。

Ultraviolet Radiation: From Skin Health to Practical Applications

Ultraviolet (UV) radiation is an invisible component of sunlight. Based on wavelength and biological effects, it is divided into three main bands: UVA, UVB, and UVC. While excessive exposure to UV radiation can damage the skin, moderate exposure also holds significant value for human health.

「Spectral Characteristics of UV Radiation and Its Effects on the Skin」

1. UVA (315–400 nm), as long-wave ultraviolet radiation, has the strongest penetrating ability. It can reach the dermis layer of the skin and easily pass through ordinary glass. This means that even indoors near a window, the skin remains exposed to UVA radiation.

Upon penetrating the dermis, UVA generates free radicals such as reactive oxygen species, which attack and degrade key structural proteins—collagen and elastic fibers. Long-term and repeated UVA exposure leads to the breakdown of the dermal structure, manifesting as deep wrinkles, skin laxity, and loss of elasticity.

As discussed in our previous issue, protection against UVA requires attention to the PA rating on sunscreen products. A higher PA value indicates better protective efficacy.

2.UVB (280–315 nm), as medium-wave ultraviolet radiation, primarily affects the epidermal layer. When the skin is exposed to excessive UVB, epidermal cells are directly damaged. In response, the body triggers an inflammatory reaction, resulting in visible erythema (sunburn) on the skin surface and an elevated risk of skin cancer. The Sun Protection Factor (SPF) specifically indicates the level of UVB protection. Daily use of SPF 30 can block approximately 97% of UVB radiation.

3.UVC (200–280 nm), although the most energetic, is largely absorbed by the atmosphere and does not pose a threat in the natural environment. However, it is important to note that artificial UVC sources (e.g., germicidal lamps) must not be directly exposed to the skin or eyes, as even brief exposure can cause burns. Strict safety protocols are essential when using such devices.

「Positive Effects and Practical Applications of UV Radiation」

Moderate UV exposure is crucial for human health. UVB stimulates the skin’s synthesis of vitamin D, a process indispensable for calcium absorption and bone health.

Thanks to its strong penetrating and fluorescence-inducing properties, UVA is widely used in anti-counterfeiting technologies for banknotes and official documents, as well as in forensic investigations. Its photopolymerization characteristics are also applied in dental restorations, electronic product coatings, and the rapid curing of printing inks.

In the medical field, narrowband UVB therapy is effective in treating skin conditions such as psoriasis and vitiligo. In agriculture, it can be used to enhance vitamin D levels in greenhouse-grown crops.

UVC’s potent germicidal properties make it valuable for disinfecting drinking water, purifying air, and sterilizing medical equipment.

These applications highlight the "dual nature" of UV radiation: when used scientifically, it benefits humanity, but overexposure can cause harm. We should neither fear UV radiation excessively nor neglect protection during prolonged exposure. With reasonable sun protection measures, we can minimize skin damage while enjoying outdoor activities, achieving a harmonious coexistence with ultraviolet radiation.