Sunscreen is a topical product used to provide protection from the sun. Often in form of a gel, lotion, cream or spray, sunscreen absorbs or reflects some of the sun's ultraviolet radiation, thus protecting the skin from sunburn and other damage.
Ultraviolet rays penetrate into the thickest layer of skin, called the dermis. The two types of rays, UVA and UVB, can suppress the immune system, thereby interfering with the body's natural ability to protect against skin cancer. UVA is the most powerful and can pass through window glass. Studies suggest that UVA exposure can prematurely age the skin, causing age spots and wrinkles. UVB rays, which cannot pass through glass, are the main cause of sunburn. Excessive exposure to either form can lead to skin cancer. Ultraviolet radiation from the sun, as well as tanning beds and lamps, have been declared as known carcinogens (cancer-causing) by the U.S. Department of Health and Human Services.
Any exposed skin must be protected daily from the sun. You should use skin protection on any day that you can see clearly without use of a light source; this includes cloudy days. Clothing and hats can provide adequate protection, depending on the material, thickness and color. Exposed skin, or skin that is underneath thin or lightly-colored clothing should be covered in sunscreen. Extra care should be taken on days with particularly harsh sun or during events with many hours of direct sun exposure.
Sunscreen should be water-resistant and should have an SPF of 30 or higher. It should provide coverage against both UVA and UVB light. Some ingredients to look for include titanium dioxide, zinc oxide, oxybenzone, ecamsule, cinoxate and avobenzone, among others.
Sunscreen should be applied approximately 30 minutes before sun exposure. It should be reapplied every hour or so, more often while swimming or sweating excessively. An adequate amount should be used, approximately one ounce for an entire body of exposed skin. Application of an inadequate amount of sunscreen will not provide full protection. Considering that a typical bottle of sunscreen is approximately 20 ounces, a family of four should use the entire bottle during a full day at the beach.
Standards regulate that sunscreen should be stable for at least three years. Replace any bottle of sunscreen that is past its expiration date, as its protective qualities will deteriorate over time.