UVB light is the type mainly responsible for sunburn, and is the type that the SPF number is concerned with. In brief, an SPF of 10 means that a person can spend 10 times the usual period in the sun before burning. But the SPF number tells nothing about the risk of damage from UVA, which can also cause wrinkling and skin aging, and increases the risk of the potentially lethal melanoma type of skin cancer. Thus it's harder to know how much UVA you're getting and for experts to gauge how much of a UVA screening ingredient is necessary for protection. Such products contain ingredients that absorb both UVA and UVB light.
Consumers can also check the ingredient list, to see that both types are included.
These types of sunscreen ingredients need some time to bond with the skin, and so they should be applied 20 to 30 minutes before sun exposure. Another type of ingredient in sun-protection products is the sun blockers. Unlike products that absorb UV light, these products reflect light away from the skin. Examples of these include zinc oxide and titanium dioxide. They emphasize that sun protection for children is very important, since a large proportion of the sun-related skin damage that is associated with melanoma occurs during the first 10 to 20 years of life.