I and II are at the highest risk. Rub It On Besides protecting you from overexposure to sunlight, sunscreens help to prevent other problems related to sun exposure, such as aging skin and precancerous growths. There are also sunscreens made for specific purposes, such as sensitive skin, scalps, and babies. Regardless of what type of sunscreen you choose, however, be sure that it blocks both UVA and UVB rays and that it has at least SPF 15. Remember that sunscreen must be reapplied throughout the day, according to manufacturer's directions, especially after swimming or exercising.
Higher numbers indicate more protection.
As a rule of thumb, you always should use a sunscreen with at least SPF 15. Though recently developed sunscreens are more resistant to loss through perspiration and removal by water than previous sunscreens were, they still should be reapplied frequently, especially during peak sun hours or after swimming or exercising. Such products actually contain chemicals that interact with the skin to protect it from UV rays. Some cosmetic products now claim to protect you from UV rays. Not all of these products, however, meet the standard of having at least SPF 15, and, as a result, do not offer sufficient protection by themselves.