There are pros and cons for both chemical and physical sunscreen, with the former causing irritation for those with skin sensitivity and being effective against the sun only 20 minutes after application. Physical sunscreens, on the other hand, defend skin immediately after application but the texture can be a little off-putting as they leave a white cast. Neither sunscreen is superior over the other, and the key is to pick one that works for you depending on your skin type and lifestyle.
It is also useful to note that sunscreen photo-degenerate, meaning they start losing their efficacy once exposed to the sun. The general rule is to apply it once every two hours, so as to maintain optimal level of UV protection. While regular sunscreen fluids make it difficult to reapply, especially over makeup, spray-on sunscreens have proven to be really useful in that aspect.