The penetration of those UV rays to the skin's inner layer is what results in the production of more melanin. That melanin eventually moves toward the outer layers of the skin and becomes visible as a tan. 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. You always should follow manufacturer directions regarding reapplication, or else you will not get the same protection from UV rays that you might think you are getting. 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. Most sun protection products work by absorbing, reflecting, or scattering the sun's rays. Such products actually contain chemicals that interact with the skin to protect it from UV rays.