Eric Rotheim's original aerosol-can patent includes the same basic elements found in cans today.

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You've probably never heard of Eric Rotheim, but you're undoubtedly familiar with his work. Rotheim, a Norwegian engineer and inventor, came up with the first aerosol-can design more than 75 years ago. The technology has evolved somewhat over the years, but the illustrations in Rotheim's 1931 U.S. patent do show most of the major elements found in today's aerosol spray cans.

Initially, Rotheim's innovation didn't have much of an impact on the world. It wasn't until World War II, when the U.S. military introduced an aerosol can for dispensing insecticide, that people fully realized the potential of the device. The easy-to-use cans were an invaluable aid for soldiers in the Pacific, where disease-carrying insects posed a deadly threat.

In the years after the war, manufacturers adapted this technology for a wide range of applications. Today, there are thousands of products packaged in aerosol cans -- everything from hair spray to cooking oil to medicine. In this edition of HowStuffWorks, we'll examine the basic principle behind these devices as well as the major mechanical elements at work inside.