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Blister Agents


Blister agents comprise a family of persistent chemical agents also known as vesicant agents. They get their name because of the wounds that they cause that resemble blisters or burns. They include the following:

  • Mustards
    Nitrogen mustard (HN-1, HN-2, HN-3) - a class of chemical warfare agent produced in the 1920s and 1930s. Nitrogen mustard comes in different forms that can smell fishy, musty, soapy or fruity. It can come in the form of an oily-textured liquid, a vapor or a solid. When in liquid or solid form, nitrogen mustards can be clear, pale or yellow-colored.

    Sulfur mustard (H, HD, HT) - also known as "mustard gas or mustard agent," was first synthesized in the 1800s and used by Germany in World War I. This chemical warfare agent can be a vapor, an oily-textured liquid or a solid. It can sometimes smell like garlic, onions or have no odor at all.
  • Lewisites (L)
    Lewisite is a chemical warfare agent that contains arsenic. In its pure form, lewisite is an oily, colorless liquid. It can appear amber to black in its impure form. Also known as "L," this agent smells like geraniums and could also be confused with ammonia.
  • Phosgene Oxime (CX)
    Specific information about this agent is very limited. It was first produced as a chemical warfare agent in 1929, but was never actually used in the battlefield. Phosgene oxime has an irritating odor. In solid form it is colorless and yellowish-brown when it is a liquid.


People can be exposed to mustard through skin contact, eye contact or breathing if the agents are released in the air. If mustards are released into the water, people can be exposed by drinking the contaminated water. Exposure can also occur as a result of coming in direct contact with liquid aerosol mustards.

If released into the air, people can be exposed to lewisite through skin contact, eye contact or breathing. People can also be exposed by drinking contaminated water or eating contaminated food. Exposure can also occur as a result of coming in direct contact with lewisite in its liquid form.

If phosgene oxime gas is released into the air, people can be exposed through skin or eye contact. They may also be exposed by breathing air that contains phosgene oxime. If the liquid form of the agent is released into water, people can be exposed by touching or drinking water that contains phosgene oxime. If phosgene oxime liquid comes into contact with food, people can be exposed by eating the contaminated food. People can also be exposed directly by coming into contact with liquid phosgene oxime.


Mustard exposure symptoms may include the following:

  • Skin burns, in which blisters can surface in as soon as 7-12 hours
  • Eye burning, irritation and swelling (blindness can occur if exposed to high concentrations)
  • Digestive tract problems such as abdominal pain, diarrhea, nausea and vomiting
  • If gas inhaled, coughing, bronchitis, long-term respiratory disease and cancer in the airways and lungs later in life

(The likelihood of death following exposure is minimal.)

Lewisite symptoms include:

  • Seconds to minutes: skin pain and irritation; immediate eye irritation, pain, swelling and tearing; runny nose, sneezing, hoarseness, bloody nose, sinus pain, shortness of breath, and cough.
  • 15 to 30 minutes: skin redness
  • Within hours: blisters; diarrhea, nausea and vomiting; low blood pressure or "lewisite shock"
  • Within days: blisters from lesions
  • Within weeks: discoloration of the skin
  • Long-term effects after prolonged exposure include skin burning, chronic respiratory disease and blindness

Immediate signs and symptoms of phosgene oxime include the following:

  • Whitening of the skin surrounded by red rings, and eventually, the development of hives. After 24 hours, the whitened areas of the skin become brown and die, and then a scab is formed. During the healing process, itching and pain may occur.
  • Severe pain, tearing and irritation in the eyes; possible temporary blindness (similar to that seen with lewisite)
  • Irritation to the upper respiratory tract, causing runny nose, hoarseness and sinus pain. Absorbing phosgene oxime through the skin or inhaling it may result in fluid in the lungs with symptoms of shortness of breath and cough.


There is no specific antidote or treatment that exists for exposure to mustard. Supportive care is usually given to a victim of the agent to minimize effects of exposure. Because there is no antidote for mustard, it is best if people avoid it. If you are in an area where mustard has been released, flee from that area immediately. Once safe, remove all clothing and wash the body thoroughly.

There is an antidote available for lewisite that is most useful when given as soon as possible after exposure. People exposed to the agent should also remove lewisite from the body and get supportive medical care in a hospital.

No antidote exists for phosgene oxime. Treatment consists of removing the phosgene oxime from the body as soon as possible and receiving supportive medical care in a hospital setting.

For more extensive information about these agents, please visit Centers for Disease Control and Prevention or U.S. Department of Health and Human Services.

Page last updated: May 13, 2021