Sunscreen is one of the most important ways to maintain a youthful appearance. The earlier in life you start using a daily sunscreen, or moisturizer that has a sunscreen in it, the less wrinkled and healthier your skin will look when you are older. Like your daily vitamins, sunscreen is preventative medicine to keep you healthy because it prevents the sun's harmful rays from damaging your skin.
The chemicals in sunscreen agents either interact with skin to prevent the sun from burning it, or physically block the sun, much the way a glove protects your hand from the sun. Blocking agents are less common than chemical sunscreens. Chemical sunscreens contain ingredients that are quickly absorbed by the skin, so you don't even know they are working. They can also be waterproof as well as sweatproof. There are two different types: those with ultraviolet B ray protection only, and those that additionally provide protection against ultraviolet A rays. (Ultraviolet B rays are the burning rays of the sun, but both Ultraviolet B and A rays contribute to skin cancer, wrinkles, and other indicators of sun damage.) The higher the SPF number is on the sunscreen label, the more protection you have against the burning ultraviolet B 'rays of the sun. In general, the best protection is found in a waterproof chemical sunscreen that is labeled with an SPF greater than 30 and also indicates that it offers protection against ultraviolet A rays.
Physical-blocking sunscreens, like body armor, protect the skin by blocking the sun's rays from ever reaching the skin's surface. Originally, sun-blocking agents, made from zinc oxide, were white pastes that were visible on your skin. Remember a lifeguard with a white paste on his nose? During the last ten years, advances in microtechnology have allowed these zinc oxide preparations and their counterparts, titanium dioxide creams, to be rubbed into the skin. These high-tech physical blocking sunscreens can also be quite water resistant, but not as waterproof and sweatproof as chemical sunscreens can be. Because of their function as an armor, physical sunscreens block all of the sun's rays, whether they are ultraviolet A or B. Physical blocking sunscreens are most effective when the ingredient silicone is added to them.
Any sunscreen should be applied for at least thirty minutes before you go out in the sun, and reapplied every few hours while you are outside. Use sunscreen liberally on your skin, or it won't provide sufficient protection. For example, you need between one-half and one teaspoon to cover your face, one teaspoon on each limb, and up to two teaspoons each on the front and back of your trunk.