Malaysian authorities announced Friday that the half brother of North Korean leader Kim Jong-un, Kim Jong-nam, was killed with the toxic nerve agent substance VX. CCTV footage shows Kim Jong-nam was approached from behind by a woman who wiped her hands on his face on Feb. 14 at the Kuala Lumpur airport. Swabs of his eyes and face taken after his death show that there was VX nerve agent on his face, which caused his death.

So what is VX nerve agent?

The Centers for Disease Control classifies VX nerve agent as a chemical warfare nerve agent. It’s a man-made odorless and tasteless oily amber-colored liquid that is similar to the Sarin but more toxic when exposed through skin contact and inhalation. “It is possible that any visible VX liquid contact on the skin, unless washed off immediately, would be lethal,” says the CDC’s site.

Like other nerve agents, VX kills those who come in contact with it by “ preventing the proper operation of an enzyme that acts as the body’s ‘off switch’ for glands and muscles.” When this happens, the glands and muscles are in a constant state of stimulation and tire to the point of full exhaustion, resulting in the stoppage of breathing.

Symptoms of exposure can set in within seconds of contamination but may take hours. It is possible to fully recover from contact with VX if it is identified, removed and treated immediately. It’s not a naturally occurring chemical and was labeled chemical weapon and banned at the Chemical Weapons Convention in 1993.