Sunscreen attempt to block and absorb UV rays through a combination of physical and chemical particles. Physical particles, such as zinc oxide and titanium dioxide, are used to reflect UV radiation from the skin. At the same time, complex chemical ingredients in sunscreen react with radiation before it penetrates the skin, absorbing the rays and releasing the energy as heat.
A combination of blocking and absorbing UV radiation is especially important to combat both UVB and UVA rays. UVB radiation is the main cause of sunburn and skin cancer. UVA rays, on the other hand, penetrate more deeply into the skin and were once thought to only cause skin aging and wrinkling. However, recent research has confirmed that UVA rays also play a significant role in the development of skin cancer. Still, many sunscreens on the market contain ingredients that only block UVB rays, thus providing insufficient protection against harmful UVA radiation.
Another factor to consider in sunscreen is the sun protection factor, or SPF. which is commonly misconceived as the strength of protection. However, it actually refers to how much longer it takes for UVB rays to redden the skin with sunscreen compared to without sunscreen. For example, an SPF of 15 means it will take 15 times longer for skin to burn while using the product compared to without the product.