SPF, known as Sun Protection Factor, indicates how effectively a sunscreen can shield the skin from UVB rays, which are responsible for sunburn, skin damage, and potential skin cancer. For instance, if your skin typically burns after 10 minutes under the sun, using an SPF 15 sunscreen would extend your time in the sun without burning to around 150 minutes (15 times longer). However, this is an approximate calculation that hinges on factors such as skin type, sunlight intensity, and quantity of sunscreen applied. It’s important to note that SPF is a gauge of protection against UVB exposure and should not be relied upon to determine duration of sun exposure.
To achieve optimal protection, specialists advise using at least SPF 30, applying the correct amount (2mg per cm2 of skin, or roughly one ounce for complete body coverage), and reapplying every 2 hours to block 97% of UVB rays.