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SPF 30 means that if applied correctly, your skin would take 30 times longer to burn than it would without protection. For instance, if you would normally burn after 10 minutes, SPF 30 theoretically allows you to stay in the sun for 300 minutes before burning.

SPF is calculated by comparing the amount of time needed to produce sunburn on protected skin versus the time needed to cause a sunburn on unprotected skin.

A 'Broad Spectrum' sunscreen offers protection against both UVB and UVA rays. The SPF number mainly indicates the level of UVB protection, but the 'Broad Spectrum' label assures some UVA protection as well.

A higher SPF offers more protection, but the difference becomes negligible past a certain point. SPF 30 blocks about 97% of UVB rays, while SPF 50 blocks about 98%. No sunscreen can offer 100% protection.

Water-resistant sunscreen means that the SPF level remains effective after a certain amount of time in the water. There are usually two categories: 40 minutes or 80 minutes of water resistance based on testing.

Wearing sunscreen is important because it helps protect your skin from the harmful effects of UVB and UVA rays, which can lead to sunburn, premature aging, and skin cancer. It's an essential part of preventive healthcare.

Traditional SPF ratings do not measure protection from UVA rays, which are also harmful and can lead to premature aging and skin cancers. Look for 'broad-spectrum' sunscreens, as these are tested for UVA as well as UVB protection.

Sunscreen should be reapplied at least every 2 hours, and more frequently if you are swimming, sweating, or toweling off. SPF protection lessens over time due to the sunscreen rubbing off or breaking down.

A general recommendation is to use approximately a shot glass (2 ounces) of sunscreen to cover the entire body. It should be applied 15 minutes before going outdoors and should be thoroughly applied to all exposed skin.