SPF (Sun Protection Factor) is a measurement of the amount of ultraviolet B (UVB) protection that a sunscreen delivers. An official standard for measuring the ultraviolet A (UVA) protection of sunscreens has been proposed but is not yet in effect. An effective sunscreen should protect against both UVA and UVB and should remain stable when exposed to sunlight.

 

Sunscreens should protect against both shorter UVB and the longer UVA rays since they both cause significant skin damage, premature aging with loss of elasticity, brown spots, pre-malignant solar keratoses, skin cancer and sun allergies.