Chemical weapons are abundant in variety. Their effectiveness is determined by several factors, including age, purity, weather conditions, and choice of dissemination. They include nerve agents, blister agents, and choking agents, all of which can be ingested through the eyes, lungs, or skin. Sarin, a type of nerve gas, was used by the Aum Shinrikyo cult in March 1995, killing 12 people and injuring more than 5,500 on a Tokyo subway.