Sunscreen protection stems from a product's ability to deflect two different types of ultraviolet radiation, UVA and UVB. Products that protect against one do not necessarily protect against both. Sunscreens are rated for their ability to protect against UVB radiation, but ratings for protection against UVA radiation are not yet standard. Resistance to sweat and resistance to water also factor into the overall sunscreen protection offered by a product.
The sun emits two different types of ultraviolet light. UVB radiation has a pronounced impact on the skin and is the main cause of sunburn but does not penetrate deeply into the body. UVA radiation is less important in causing sunburn but penetrates the skin more deeply and is a main cause of the weathered appearance that skin takes on after prolonged sun exposure. Both types of ultraviolet light can cause cancer.
Most sunscreens are rated with a sun protection factor, or SPF. This number roughly translates to the factor by which effective sun exposure is reduced. An SPF of ten reduces sun exposure by a factor of ten, so that ten hours of exposure would be needed to produce the results normally seen after one hour. This factor indicates only the UVB protection offered by a given product and is a rough guideline rather than an absolute rating. It is best to err on the side of caution and choose products with a higher SPF rating.
UVA protection is not rated on a standard scale. In most nations, sunscreens will now indicate whether they offer this sort of protection, often by advertising “full-spectrum” protection. This type of sunscreen protection should be chosen whenever possible.
Proper application of sunscreen is essential. For maximum sunscreen protection, application directions should be followed exactly. Many people under-apply sunscreen, leading to reduced protection. The periodic re-application of sunscreen, as directed, is also essential for maintaining full sunscreen protection, as all types of sunscreen wear off and lose their effectiveness over time. Re-applying every two hours is typically necessary.
Each sunscreen formula is different, and some are better at resisting wear and water. Sunscreen protection is greatly influenced by these differences. All sunscreens degrade when exposed to water and as the body sweats. Products designed for aquatic or sport use, however, are more resistant to this degradation. Each product should include specific directions relating to activity and water exposure, and directions for application and re-application should be followed to ensure maximum sunscreen protection.
