Sunscreen, which is also commonly known as sunblock or suntan lotion, is a lotion, gel, spray, or other topical product that is designed to absorb or reflect some of the ultraviolet (UV) radiation from the sun on skin that is exposed to sunlight. Sunscreen helps to protect the skin against sunburn. Sunscreens can be classified into to 2 categories, depending on the mode of action: physical sunscreens reflect the sunlight, and chemical sunscreens absorb the UV light.
In addition to helping to protect skin from sunburn, sunscreen use can help prevent melanoma and squamous cell carcinoma, two types of skin cancer. However, there is little evidence that it is effective in preventing basal cell carcinoma.
There are many sunscreens available that do not block UVA radiation. The UVA ray does not primarily cause sunburn, but it can increase the rate of melanoma and cause premature aging of the skin (wrinkles and age spots). Individuals using sunscreens may be exposed to high levels of UVA without realizing it. To avoid this problem, broad-spectrum sunscreens are available that protect skin from both the UVB ray, associated with sunburn, and the UVA ray, associated with pre-mature aging of the skin. Using broad spectrum sunscreen diligently can slow or temporarily prevent the development of sagging skin and wrinkles.
The SPF (Sun Protection Factor) rating is how sunscreen protection is measured; it is a measure of the fraction of sunburn-producing UV rays blocked. For example, “SPF 30” means that 1/30th of the burning radiation will reach the skin, assuming that the sunscreen is applied evenly at a think dosage of 2 milligrams per square centimeter. A user can determine how effective a sunscreen will be for them individually by multiplying the SPF factor by the length of time it takes them to suffer and sunburn without sunscreen. It is important to note that sunscreens with a higher SPF do not remain effective on the skin any longer than lower SPFs, and must be reapplied continuously as directed, usually every 2 hours.