I'm cheating a little here and posting a condensed version of info I posted on my other blog.
There are two types of sunscreens, chemical and physical. Chemical sunscreens are synthetic and provide protection from the sun by being absorbed into the skin. Chemical sunscreens feel lighter on the skin and generally have a higher SPF level than physical sunscreens. However, chemical sunscreens are more likely to irritate sensitive skin. Apply chemical sunscreens at least 20 minutes before heading outside since they need time to absorb into the skin.
Physical sunscreens are the natural sunscreens that provide protection from the sun by sitting on top of the skin. They reflect or scatter ultraviolet light as it hits the skin forming a barrier between your skin and the sun. They start to work almost immediately after applying. The most common natural sunscreens are the natural minerals zinc oxide and titanium dioxide. These mineral compounds work by reflecting UVA rays and have long-standing safety records.
Antioxidants are often combined with titanium dioxide to slow down the oxidation of oils. Some popular natural antioxidants are vitamins E and C, rice bran oil (SPF 4), sesame seed oil (SPF 4), natural shea butter (SPF 6), and green tea (increases the sun protection activity of ingredients).
Recent research also shows that antioxidant supplementation may protect our skin. A paper published in the American Journal of Clinical Nutrition found that supplementation with carotenoids (25 mg/day) and vitamin E (500 IU/day) "may be useful for diminishing sensitivity to ultraviolet light."