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Blister agent toxicity

Author: Vanessa Ngan, Staff Writer. Minor revision, February 2014.

Table of contents

What are blister agents?

Blister agents are common chemical warfare agents. Sulphur mustard was used extensively during World War I and then more recently in the Iran-Iraq War (1980-1988). The most apparent toxic effect of blister agents is the damage they cause to skin. They produce slow-healing skin lesions which can blister, ulcerate and promote secondary infections. These blister agents are also called vesicants.

Classification and chemical properties of blister agents used in warfare

There are four main blister agent chemicals:

  • Lewisite (L, L-1, L-2, L-3)
  • Sulfur mustard (H), previously also spelt ‘sulphur’ (British) and commonly known as mustard gas
  • Nitrogen mustard (HN-1, HN-2, HN-3)
  • Phosgene oxime (CX)

The letter/numbers following the chemical name are the military designations given to the blister agents.

The following table displays some chemical properties of the blister agents.

Lewisite Sulfur mustard Nitrogen mustard Phosgene oxime
Physical form Oily liquid Oily-textured liquid, gaseous vapour, solid Oily-textured liquid, gaseous vapour, solid Liquid, solid
Characteristic odour Geraniums Garlic, onions, mustard, or odourless Fishy, musty, soapy, fruity An irritating, disagreeable odour
Colour Colourless in pure form. Amber to black in impure form. Clear to yellow or brown Clear, pale amber or yellow Colourless in solid form. Yellow-brown in liquid form.

What are blister agents used for?

All these blister agents were produced as potential chemical warfare weapons. Only lewisite and sulfur mustard have ever actually been used at war. Some nitrogen mustards were designed to remove warts and treat cancers, but have now been replaced with safer and more effective agents. Historically, sulfur mustard has been used to treat psoriasis but has no medical use today.

Blister agents are relatively easy to produce and large stockpiles of these agents may be present in several countries. There is always the underlying threat that they can be used in a terroristic attack.

What are the signs and symptoms of blister agent toxicity?

Signs and symptoms differ slightly between the different blister agents.


Signs and symptoms occur immediately after exposure.

Skin effects:

  • Pain and irritation occur within seconds to minutes and is followed by redness of the area within 15 to 30 minutes.
  • Blisters begin to form within several hours and start as a small blister in the middle of the red areas which then expand to cover the entire area of affected skin.
  • Sores heal much faster than sores caused by the other blistering agents and skin discolouration that occurs later is much less noticeable.

Other system effects:

  • Eye irritation, pain, swelling and tearing may occur on contact.
  • Respiratory symptoms such as a runny or bleeding nose, sinus pain, sneezing, hoarseness, cough and shortness of breath may occur.
  • Diarrhoea, nausea and vomiting may occur.
  • “Lewisite shock” may cause sudden low blood pressure.
  • Extensive exposure may cause blindness and chronic respiratory disease.

Sulfur mustard

Signs and symptoms do not usually occur immediately after exposure. Depending on the severity of the exposure, symptoms may not occur for up to 24 hours. People who are more sensitive to sulfur mustard may show signs and symptoms earlier. Often people may not know immediately that they have been exposed, because sulfur mustard may not have a smell or have a smell that causes alarm.

Skin effects:

  • Redness and itching of the skin may occur 2 to 48 hours after exposure.
  • Yellow blistering of the skin occurs soon after.
  • Exposure to sulfur mustard liquid is more likely to produce second- and third- degree burns and later scarring compared with exposure to sulfur mustard vapour.
  • Extensive skin burning can be fatal.

Other system effects:

  • Eye irritation, pain, swelling, and tearing may occur within 3 to 12 hours of mild to moderate exposure. Results of severe exposure may be apparent within 1 to 2 hours and include symptoms of a mild or moderate exposure plus light sensitivity, severe pain, or blindness lasting up to 10 days.
  • Respiratory symptoms such as a runny or bleeding nose, sinus pain, sneezing may occur within 12 to 24 hours of a mild exposure and within 2 to 4 hours of a severe exposure.
  • Abdominal pain, diarrhoea, fever, nausea, and vomiting.
  • Aplastic anaemia (decreased formation of blood cells) or pancytopenia (decreased red or white blood cells and platelets) leading to weakness, bleeding and infections.
  • Extensive exposure may cause permanent blindness, chronic respiratory disease, and repeated respiratory infections. It may also increase a person’s risk for lung and respiratory cancer.

Nitrogen mustard

Signs and symptoms usually do not occur immediately but depend on the severity of the exposure. Symptoms may not occur for several hours after exposure.

Skin effects:

  • Redness usually develops within several hours after exposure followed by blistering within 6 to 12 hours.
  • Nitrogen mustard liquid is more likely to produce second- and third- degree burns and later scarring compared with exposure to nitrogen mustard vapour.

Other system effects:

  • Eye irritation, pain, swelling, and tearing may occur. High concentrations can cause burns and blindness.
  • Respiratory symptoms such as nose and sinus pain, cough, sore throat, and shortness of breath may occur within hours.
  • Abdominal pain, diarrhoea, nausea and vomiting.
  • Tremors, incoordination and seizures are possible after exposure to high concentrations.
  • Bone marrow suppression may occur 3 to 5 days after exposure. This causes anaemia, bleeding, and increased risk for infection. If severe, these effects could lead to death.
  • Some evidence exists that repeated or prolonged exposure can cause leukaemia.

Phosgene oxime

Signs and symptoms occur immediately after exposure.

Skin effects:

  • Pain occurring within a few seconds, and blanching (whitening) of the skin surrounded by red rings occurring on the exposed areas within 30 seconds.
  • Within about 15 minutes, the skin develops hives. After 24 hours, the whitened areas of skin become brown and die, and then a scab is formed.
  • Itching and pain may continue throughout the healing process.

Other system effects:

  • Severe eye pain and irritation, tearing, and possibly temporary blindness.
  • Respiratory symptoms include immediate 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 (pulmonary oedema) with symptoms of shortness of breath and cough.

What is the treatment for blister agent toxicity?

The most important factor in the treatment of blister agent toxicity is removing the blister agent from the body. Remove and seal off in a double plastic bag any contaminated clothing. Seek emergency medical attention immediately. Lewisite is the only blister agent with a known antidote. Exposure to blister agents is not usually fatal if patients receive immediate supportive medical care to minimise the effects of exposure.

Sulphur mustard was heavily used in the Iran-Iraq War and currently there are about 30,000 victims still suffering from the late effects of the agent. Chronic obstructive lung disease, lung fibrosis, recurrent corneal ulcer disease, chronic conjunctivitis, abnormal pigmentation of the skin, and several forms of cancer, are just some of the long-term effects of their exposure.



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