Blister agent

A blister agent (also known as a vesicant) is a chemical compound that causes severe skin, eye and mucosal pain and irritation. They are named for their ability to cause large, painful water blisters on the bodies of those affected. Although these compounds have been employed on occasion for medical purposes, their most common use is as chemical warfare agents.

Most blister agents fall into one of three groups:
 * Sulfur mustards – A family of sulfur-based agents, including the so-called "mustard gas".
 * Nitrogen mustards – A family of agents similar to the sulfur mustards, but based on nitrogen instead of sulfur.
 * Lewisite – An early blister agent that was developed, but not used during World War I. It was effectively rendered obsolete with the development of British anti-Lewisite in the 1940s.

Occasionally, phosgene oxime is included among the blister agents, although it is more properly termed a nettle agent.

Effects of blister agents
Exposure to a weaponized blister agent can cause a number of life-threatening symptoms, including:
 * Severe skin, eye and mucosal pain and irritation
 * Skin erythema with large fluid blisters that heal slowly and may become infected
 * Tearing, conjunctivitis, corneal damage
 * Mild respiratory distress to marked airway damage

All blister agents currently known are heavier than air, and are readily absorbed through the eyes, lungs, and skin. Effects of the two mustard agents are typically delayed: exposure to vapors becomes evident within 4 to 6 hours, and skin exposure in 2 to 48 hours. The effects of Lewisite are immediate.