Sunblock protects your skin from the sun's ultraviolet (UV) rays. You should apply sunblock every time you go outdoors, even during the winter months. The University of California School of Medicine reports on its website that clinical trials indicate SPF 30 offers significantly more protection than SPF 15, so the medical institution now recommends using a sunblock with a minimum of SPF 30.
Significance
Sunblock prevents harmful UVA and UVB rays from coming into contact with your skin. This can help you prevent skin cancer and ward off the effects of sun-induced skin aging. Wearing sunblock will also allow you to stay outdoors in the sun longer without getting sunburn.
Types
Sunblock comes in two varieties: physical and chemical. Chemical sunblock absorbs UV radiation before it reaches your skin. Physical sunblock reflects or scatters UV radiation so it doesn't reach your skin. Physical sunblocks are made from zinc oxide, which is a thick white paste, or titanium dioxide, which is less visible. Some sunblock formulas combine a physical sunblock with a chemical one for maximum protection. Sunblock is available as a lotion, gel, cream, stick, oil or spray. Look for a product that protects against both UVA and UVB rays.
Function
Physical sunblocks are effective at blocking UVA and UVB rays. Many of the chemical sunblocks work on UVB rays, but only a few block UVA rays. For that reason, chemical sunblocks typically contain a mixture of ingredients so you are protected against a wide spectrum of UV rays.
Time Frame
Sunblock should be applied 20 minutes before you go into the sun. If you sweat or go swimming, you should reapply it frequently. Water-resistant sunblock is available that allows you to swim for up to 40 minutes. Sunblock labeled "very water resistant" retains its SPF protection for up to 80 minutes of water contact. In addition, the University of California School of Medicine website advises that sunblocks, even if you stay dry, may lose effectiveness in about two hours, so you should reapply it often when you are in the sun.
Considerations
Sunblock needs to be applied in adequate amounts, or its effectiveness could drop. You should apply at least one half teaspoon of sunblock to your face and neck, according to the Michigan State University website. You should rub the sunblock into your skin when you apply it so the ingredients can penetrate the skin. You may prefer the feel of a lotion, but oily sunblocks tend to penetrate and remain in your skin longer. If your skin is irritated by sunblock, check to see if it contains PABA and switch to a brand without it. According to the University of California School of Medicine website, sunblocks with zinc oxide or titanium dioxide rarely cause skin reactions and are gentle enough to use every day.
