紫外线：从皮肤健康到生活应用

紫外线是太阳光中不可见的辐射光。根据波长及其生物效应，可划分为UVA、UVB和UVC三个主要波段。虽然过度暴露于紫外线会对皮肤造成损害，但适量接触亦对人体健康具有重要价值。

「紫外线的光谱特性与皮肤影响」

1、UVA（315-400nm）作为长波紫外线，穿透力很强，不仅能直达皮肤真皮层，也可轻易穿透普通玻璃。这意味着即使在室内靠窗位置，皮肤仍会受到UVA辐射。UVA深入真皮层后，会产生活性氧簇等自由基，攻击并降解胶原蛋白和弹性纤维这些关键结构蛋白——胶原蛋白和弹性纤维。长期且反复的UVA暴露，会导致真皮层结构塌陷，表现为皮肤出现深皱纹、松弛、失去弹性。

上一期我们介绍过，针对UVA的防护，我们需要关注防晒产品上的PA标识，PA值越高，防护效果越好。

2、UVB（280-315nm）作为中波紫外线，主要影响表皮层。当皮肤暴露于过量UVB时，表皮细胞会直接受损。身体为应对此损伤，会启动炎症反应，皮肤表面形成肉眼可见的红斑，即晒伤，并增加患皮肤癌的风险。SPF值专门标示对UVB的防护等级，日常使用SPF30即可阻挡约97%的UVB。

3、UVC（200-280nm）虽然能量很强，但绝大多数被大气层吸收，自然环境中不对人体构成威胁。但需注意，人工UVC光源（如杀菌灯）不可直接照射人体，其短时照射即可灼伤皮肤与眼睛，需严格规范使用。

「紫外线的积极作用与生活应用」

适量紫外线对人体健康至关重要。UVB能促进皮肤合成维生素D，这一过程对钙质吸收和骨骼健康具有不可替代的作用。

UVA凭借其出色的穿透与荧光激发能力，常用于钱及证件防伪鉴定、刑侦取证，其光固化特性也广泛应用于牙科修复、电子产品涂层和印刷油墨的快速固化。

UVB在医疗领域中，窄谱UVB是治疗银屑病等皮肤病的有效方法；在农业上，可用于提高温室作物中维生素D的含量。

UVC因其高效的杀菌消毒能力，被广泛用于饮用水净化、空气消毒及医疗器械的无菌处理。

这些应用充分体现了紫外线的“双面性"：科学利用可造福人类，过度暴露则会造成伤害。我们既不应过度恐惧紫外线，也要避免无防护的长时间暴露。通过合理的防晒措施，在享受户外生活的同时，尽可能限度降低紫外线对皮肤的伤害，实现人与紫外线的和谐共存。

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.