Americans spend countless dollars on sunscreen each and every year. While everyone is familiar with sunscreen, listed below are some things you probably didn’t know about this common household item.

SPF Doesn’t Catch Everything – Many sunscreens advertise their SPF (sun protection factor) content. It bears mentioning, however, that SPF content only shields the skin from UVB rays; UVA rays are not blocked by many sunscreens.

Sunscreen Should be Applied to “Forgotten Areas” – Do you apply sunscreen to your ears, hairline, neck, feet and hands? If the answer is yes, then congratulate yourself on a job well done. Many Americans neglect these areas, result in numerous avoidable sunburns.

Tattoos Don’t Save Your Skin – It seems that more people than ever are sporting tattoos. While they might look pleasing (depending on your point of view, of course) they shouldn’t be viewed as a sunlight barrier; tattooed parts of the skin still need protection.

Sunscreen Works on Scars – To add insult to injury, scarred skin can likewise fall victim to sunburn. In fact, scarred skin is more likely to be stricken with cancerous tumors. To prevent this, use a sunscreen of with a SPF of at least 35 to cover any scars.

30 Is the Magic Number – Next time you go sunscreen shopping, keep the number 30 in mind. A sunscreen with a 30 SPF will intercept 97 percent of incoming UV rays. You may also consider springing for 50 SPF sunscreen, which will prevent 98 percent of ultraviolet rays from reaching the skin.