Sulfur is a bright yellow chemical element that can smell like rotten eggs, especially in gases released from hot springs or volcanoes. You might recognize that sharp, unpleasant smell from fireworks, matches, or hot springs, where sulfur naturally occurs.

This element has been known since ancient times. The ancient Greeks used sulfur in medicines and for bleaching cloth. In medieval times, people called it brimstone, and because it burned with an eerie blue flame and produced choking fumes, writers often associated it with hellfire and destruction.

Today sulfur is essential for modern life. Factories use it to make sulfuric acid, one of the most important industrial chemicals, which helps produce fertilizers that help farmers grow food for billions of people. Your body actually needs small amounts of sulfur to build proteins and stay healthy.

Sulfur appears in nature in several ways: as pure yellow crystals near volcanoes, mixed into minerals like pyrite (fool's gold), and dissolved in petroleum. When volcanoes erupt, they release sulfur dioxide gas, which can affect the weather by blocking sunlight. Scientists use the chemical symbol S for sulfur and assign it atomic number 16 on the periodic table.