Zinc oxide is a strong defence against the sun and other irritants. It is used in cosmetics as a thickening, whitening, lubricating, and sunscreen agent. Zinc oxide, like titanium dioxide, is thought to pose no risk of skin sensitisation. It works well as a sunscreen because it protects against both UVA and UVB rays. It has some astringent, antiseptic, and antibacterial properties. 

Concerns have been raised in recent years regarding the use of nano-sized zinc oxide in sunscreen formulations. Nanotechnology is the process of shrinking a substance to a fraction of its original dimension. In the case of zinc oxide, nanotechnology is used to boost its visual appeal as well as its SPF. Skin safety is not considered to be a problem with nano-sized zinc oxide.

See also:
UVA
UVB
Titanium Dioxide