Skunk spray comes out both in a stream and a spray simultaneously from two glands on either side of the skunk’s anus. The skunk can shoot its stream with a high degree of accuracy up to 16 feet. Once a skunk sprays, it can take up to days to regenerate a fresh supply. The spray itself is an organosulfur compound composed mainly of thiols or mercaptans. 

The smell can be detected by humans up to 3 miles away.

Here is the chemical formula: