SPF stands for Sunburn Protection Factor. There are two categories of UV light: UVA and UVB.
UVA causes aging and UVB causes burns. SPF numbers are for UVB rays only. PPD, which stands for persistent pigment darkening, is the term used to measure UVA. SPF helps to prevent sunburns and PPD guards against photoaging. It is important to have a broad spectrum sunscreen to protect against both types of UV rays.
Sunscreen with a UV protection above 30 can give a false sense of security since these numbers do not offer significantly more protection from the suns rays.
So here's how SPF numbers work. The idea is that if it takes, say, 10 minutes of sun exposure to cause a burn, an SPF15 will allow you to be in the sun for 10 minutes X 15 or 150 minutes without burning. This equation is non-linear. An SPF70 will not give protection for 700 minutes.
An SPF15 absorbs 93.3 percent of UVB rays. An SPF30 absorbs 96.7 percent. Even though the SPF number doubled, the absorption has increased only slightly. An SPF50 absorbs 98 percent. As you can see, once an SPF30 is reached protection does not increase dramatically. The FDA has stated that any sunscreens labeled higher than SPF30+ are misbranded.
Butterbean sunscreens are third party tested to ensure an SPF of 30. SPF is dependent on the proper application of the sunscreen. In the FDA SPF test, approximately a full ounce of sunscreen is used to cover an adult body. It is important when using mineral sunscreens that you apply enough sunscreen to cover the skin well. Applying half the amount of sunscreen can leave you with a significantly lower SPF. Remember, mineral sunscreen sits on the surface of the skin. If the sunscreen is rubbed off by towel drying, sand, surf, sweat, or other, protection will be decreased.