SPF stands for Sun Protection Factor. It measures how long you can be in the sun before you will burn. So, for example, if you would normally burn in fifteen minutes without protection, then wearing a sunscreen with SPF 15 should protect you fifteen times as long.
However, SPF numbers are not like simple math. They don’t add up. For example, if you are wearing a moisturizer with an SPF of 15 and a mineral makeup foundation with an SPF of 15, you are not wearing SPF 30. To complicate this further, you are likely wearing more than 15 –simply due to the heavier physical coverage of product on your skin.
Also, the difference in SPF – for example going from an SPF 15 to an SPF 30 doesn’t actually double your safety zone since SPF 15 purports to block 93 to 95% of UVB rays, while SPF 30 should provide 97% coverage.
As with all products, its important to check the active ingredients of the product, which will influence how effective the product will be. Its also advisable to use a wide spectrum product that blocks both UVA and UVB rays.
For women who wear makeup and don’t want to reapply wet sun screen, I highly recommend Glo Mineral’s SPF 30 Mineral Powder, which comes in bronze and translucent. It’s got a lovely light consistency and comes with the brush attached so its great for your purse.
When considering what level SPF to use I, personally, recommend values of 40 or less. Reapplication is perhaps the most important part of using sunscreen. This will ensure that your skin is still well protected regardless of the SPF factor, sweating or swimming. And don’t scrimp on that layer of sunscreen – remember that when the products are tested, most likely they’re using a nice, thick layer to get that SPF rating – so slather that stuff on well.