Double the Number Doesn't Mean Double the Dose.
If you think that SPF 100 must be twice as strong as SPF50, think again. While SPF 15 through 50 provides protection for that number multiplied with however many minutes it would otherwise take you to burn, sunscreen above SPF 50 only incrementally increases your protection. In fact, the Food and Drug Administration (FDA in the USA) recently banned brands from declaring an SPF over 50 to prevent consumer confusion.

Multiples Don't Add Up.
If your foundation has SPF in it, as well as your moisturizer, the resulting sun protection you're getting unfortunately isn't simply the addition of both numbers. Rather, your protection level is the highest number of the two – and make sure you've applied the product generously enough.

Only Certain Clothes Protect.
Clothing can act as an excellent form of UV protection, though not all pieces are equally protective. Tightly woven fabrics like denim, rayon and wool keep out the most rays, while light and airy cottons and crepe allow some rays to penetrate. Also, deep hues like blue, red and black provide significantly more protection than light pastels and white. Wide-brimmed hats are always recommended to help boost sunscreen protection on your face.

There's No Such Thing As Waterproof.
Unlike mascara, SPF can't be formulated as waterproof. The closest it can deliver is water-resistant, and these formulations are labeled as such. If you're in the water or sweating while sporting, you should also reapply sunscreen every two hours.

Ears Are A High Rish Area.
While you may carefully apply sunscreen all over your face to prevent skin cancer, the third greatest risk area is actually around your ears. In a recent Skin Cancer Foundation study of 2,785 patients, 269 patients had basal cell carcinoma in this often-forgotten area. So the next time you apply your favourite SPF, don't forget your ears – no matter what season.

Sunscreen Always Comes Last.
A popular skincare rule recommends applying products from thinnest to thickest ; for example, from toner to serum to moisturizer. However, sunscreen is one exception that is always the final skincare step, no matter the consistency. This ensures you get the maximum amount of protection – and the rest of your skincare products will work better, too.