As summer approaches, I thought you should all be experts on sunscreen. Sunlight is good for us in many ways, helping with our mood and the production of vitamin D. However, the ultraviolet (UV) rays that come with it can cause skin cancer, wrinkles, and dark spots. The UVB rays are thought to be the most harmful, but only a small amount of UVB actually reaches our skin. More UVA rays reach our skin and even though they are thought to be less harmful than UVB, they can also lead to skin damage and cancer. Finding a good sunscreen means finding one with both UVA and UVB protection. These are labeled as "broad spectrum."
There are two types of sunscreens: organic (chemical) and inorganic (physical). The organic sunscreens produce a chemical reaction on the skin that absorbs the UV rays and releases a small amount of heat. The inorganic sunscreens work by blocking or reflecting the UV rays. There are pros and cons about each. There is a concern about organic sunscreens (oxybenzone and avobenzone) increasing estrogen levels in the body. The inorganic sunscreens (titanium dioxide and zinc oxide) are very safe and effective, however, many people find them difficult to use as they are thick and leave a white film on the skin. They have developed nanoparticle (very small sized particles) types of inorganic sunscreens that do not show as much in the skin, however, there are concerns that these nanoparticles might be absorbed and cause toxicity.
The SPF (sun protective factor) measures the ability to protect against UVB, but not against UVA. In general, you should look for an SPF above 30, however, it's more important to have a broad spectrum sunscreen than a high SPF sunscreen.
Keep in mind that even water-resistant sunscreen will wash off, so you will have to reapply it after you swim or sweat. Overall, remember a little bit of sunshine is ok, but you should try to limit your sun exposure by wearing clothing, or staying in the shade. If you have to be out in direct sun for extended periods, I recommend you use a broad spectrum sunscreen.