Sarin: colorless, tasteless, odorless. A weapon of mass destruction impossible to detect until it’s already too late. An agonizing death, unless an antidote is administered quickly. Those who escape death may still suffer permanent neurological damage. The World Health Organization recognizes Sarin as 26 times more deadly than cyanide gas.

On April 4, the residents of Khan Sheikhoun, a Syrian rebel stronghold west of Aleppo, were assaulted by Syrian Air Force attack jets. While attacks on civilians from the Syrian government are nothing new, this instance was something different. Previous bombings had used mainly chlorine and mustard gas, and casualties were usually relatively low.

That afternoon, first responders reported finding more than six hundred Syrians convulsing on the ground, paralyzed with pinpoint pupils, foaming at the nose and mouth and struggling to breathe. According to the Syrian Observatory for Human Rights, the death toll has risen to 86 people, with 27 of the victims being children.

Assessments performed by US Intelligence officials, Doctors Without Borders, the UN Health Agency, and a report from a Turkish hospital suggest that a combination of chlorine gas and sarin were used in this attack. Officials in Damascus admit to launching the airstrike on Khan Sheikhoun but argue that the bombs they dropped were not chemical in nature. Syrian allies in Moscow allege that the government’s bombs had struck a pre-existing rebel chemical stockpile. Chemical arms experts argue that if this were the case, the gases would not have been dispersed to such effect.

In 1925, the Geneva Protocol banned the used of chemical weapons in international armed conflicts. The production and stockpiling of sarin was officially outlawed by the Chemical Weapons Convention of 1993, to which Syria became a signatory in 2014.

Sarin was also deployed in August 2013, against Syrian rebels in Ghouta. Reports from UN chemical weapons inspectors suggest the attack killed 1400 men, women, and children. As a result of the international backlash following this massacre, Syria joined the Chemical Weapons Convention. President Bashar Al-Assad agreed to surrender Syria’s stockpile of 2.8 million pounds of toxic weapons and to shut down Syria’s chemical weapons program. In 2014, they allegedly handed over the last few metric tons declared by the country. Some suspect Al-Assad had nerve agents preserved and stowed away.

Sarin was developed in the late 1930s by a team of German chemists. The substance, which would later be recognized by the CDC as the most volatile of all nerve agents, was the accidental offspring of a pest control project. Dr. Gerhard Schrader’s team was charged with developing insecticides that would allow Germany to be less reliant on imported food sources. He alerted his superiors of his creation, and before long, German military scientists were mass producing the gases and packing them into bombs and artillery shells.

Nerve agents like sarin block an an enzyme called cholinesterase, which breaks down acetylcholine. Acetylcholine is a neurotransmitter that plays a role in muscle contraction and neural signaling. When this enzyme is blocked, nerve cells in the brain and muscular system become stuck in a state of overstimulation. This overstimulation can lead to paralysis, and the other symptoms witnessed by first responders.

The United States responded by firing fifty tomahawk missiles at a Syrian air base. Fighting with fire with fire leaves an earth well scorched.