Chemical weapons are toxic chemical agents deliberately used to cause death or severe harm. They are, by far, the most widely used and proliferated weapons of mass destruction, though they often get less attention than nuclear or biological weapons. That changed in 2013 when chemical weapons were used in the Syrian Civil War, and graphic images of the victims showed the world the devastating capacity of these weapons.

The different types of chemical weapons

Chemical weapons use several different properties to debilitate or kill people, animals, and plants. Blister agents cause skin, eye, and lung irritation. Choking agents cause severe and painful breathing problems, leading to suffocation. Blood agents stop blood from distributing needed oxygen throughout the body. Nerve agents debilitate the nervous system, causing muscle contraction, loss of control over bodily functions, and death within minutes.

Eliminating chemical weapons
The use of these weapons in war, first in World War I and later in the Iran-Iraq War, in Syria and elsewhere, had such disturbing effects that the international community agreed to a complete ban on chemical weapons in 1993. Participation in the Chemical Weapons Convention, which obliges countries not to develop, produce, stockpile, or use chemical weapons, is nearly universal. Seven countries have eliminated their chemical weapons altogether and six still have more work to do. Two countries signed up to the ban—the United States and Russia—are still working to destroy massive chemical weapons stockpiles, and progress has been slower than expected.

A handful of key countries—particularly in the Middle East—remain outside of the treaty. North Korea is also outside the treaty and is believed to have chemical weapons capable of being deployed across multiple delivery systems.

The Dual-Use Challenge
Chemical agents are also widely used for commercial, industrial and research purposes in countries around the world. Though these chemicals are meant for peaceful purposes, countries and non-state actors alike have exploited their dual-use nature. It doesn't take cutting edge technology or deep expertise to develop chemical weapons—just an understanding of chemistry and access to designs and "how-to" information, which is widely available on the internet.

Unlike nuclear, biological and radiological weapons, chemical weapons already have been used by non-state actors and terrorist organizations. In 1995, a Japanese religious group called Aum Shinrikyo released liquid sarin on the Tokyo subway, which evaporated quickly into a colorless and odorless gas that attacked passengers' nervous systems.  The attack killed 17 people, and sent more than 5,500 patients to the hospital.  More recently, reported chemical weapon use by ISIL in Syria shows growing interest in chemical weapons from non-state actors.