For full protection, apply an ample white coat to all exposed skin, then rub in to reduce whitening effect. Some separation may occur. Knead tube before use. Reapply after swimming and sweating as needed. Children under 6 months of age: ask a doctor.
What is SPF?
SPF, or Sun Protection Factor, is a measurement of how well a sunscreen will protect skin from UVB rays, the kind of radiation that causes sunburn and is thought to contribute to some types of skin cancer.
If your skin would normally burn after 10 minutes in the sun, applying an SPF 15 sunscreen would allow you to stay in the sun without burning for approximately 150 minutes (a factor of 15 times longer). This is a rough estimate and depends on skin type and intensity of sunlight. For best protection, experts recommend using a sunscreen with a minimum SPF rating of 15, and applying sunscreen generously and frequently.
But SPF isn't quite that simple, the scale is not linear. SPF15 sunscreen blocks about 93% of UVB rays, SPF30 sunscreen blocks about 97% of UVB rays and an SPF50 blocks 98% of UVB rays. So SPF30 sunscreen does not give you twice the protection of SPF15 sunscreen! And an SPF50 sunscreen is only 1% more effective than an SPF30 sunscreen.