Sunblock, or sunscreen, is a term used to describe products that protect your skin from the harmful effects of the ultraviolet radiation contained in sunlight. Proper use of a sunblock product can help protect you from wrinkles and skin damage, in addition to lowering your risks for the development of skin cancer. However, no sunblock can fully prevent the possibility of disease development.
Sunlight Basics
Sunlight has both visible and invisible components, according to the American Academy of Dermatology, or AAD. Ultraviolet radiation -- which contains both ultraviolet A, or UVA, and ultraviolet B, or UVB -- belongs to the invisible spectrum of sunlight. Exposure to the UV content in sunlight is what triggers the onset of suntans and sunburns. You can develop skin cancer or other serious skin damage as the eventual consequence of a single bad sunburn or from long-term habitual exposure to unfiltered sunlight.
Sunblock Basics
Sunblocks and sunscreens achieve their protective effects by scattering, absorbing or reflecting sunlight, the AAD reports. Traditional products are mainly designed to protect you from sunburns, which result from exposure to UVB; their effectiveness in this regard is measured in terms of their sun protection factor, or SPF. Modern forms of sunscreen may also provide broad-spectrum protection from both UVB and UVA. However, scientists do not currently have a standard method of measuring the effects of UVA, the American Cancer Society explains, and SPF numbers do not indicate your level of protection from UVA exposure.
Effectiveness
Sunscreens with an SPF of 15 stop roughly 93 percent of UVB from reaching your skin, the American Cancer Society reports. Sunscreens with an SPF of 30 block out roughly 97 percent of UVB. Sunscreens with an SPF of 50 block out roughly 98 percent of UVB, while products with an SPF of 100 block out about 99 percent. There are no products available that can provide 100 percent protection from UVB exposure. As a minimal standard for protection, the AAD recommends that you use sunscreens with an SPF of 30.
Proper Application
To gain the benefits of sunscreens or sunblocks, you must apply them properly to your skin, the American Cancer Society notes. If you are an adult, you will need about 1 oz. of sunscreen to fully cover exposed areas such as your face, legs, neck and arms. To maintain full protection, you will also need to reapply sunscreen a minimum of every two hours. Sweating or swimming will shorten this reapplication time. If you use a "water-resistant" product and expose yourself to water through swimming or sweating, you will need to reapply sunscreen about every 40 minutes. If you use a "waterproof" product, you will need to reapply it roughly every 80 minutes under the same circumstances.
Considerations
Most people do not apply adequate amounts of sunscreen, and therefore inadvertently decrease their sun protection, according to the Skin Cancer Foundation. To provide full skin protection, you will need to apply sunscreen at least 30 minutes prior to sun exposure. Reapply sunscreen whenever you towel off during outdoor activities.
