Sulfur mustard, commonly known as mustard gas, is a synthetic chemical warfare agent classified as a vesicant, or blistering agent. First used extensively during World War I, this oily liquid or vapor attacks the skin, eyes, and respiratory tract upon contact. Despite its name, the substance is not actually a gas but a liquid that readily vaporizes, often possessing an odor resembling garlic, onions, or mustard when impure. Exposure is rarely immediately fatal but causes severe, debilitating injuries, often leading to prolonged illness and long-term health complications.
The Mechanism of Cellular Damage
Mustard gas functions as a potent alkylating agent, chemically adding alkyl groups to biomolecules, primarily DNA and proteins within the cells. The agent reacts with the N7 position of guanine bases in the DNA strands, causing cross-links and breaks in the genetic material. This irreparable damage prevents the cell from successfully dividing and replicating its DNA, making it particularly destructive to tissues with high cell turnover rates.
The cellular disruption rapidly triggers programmed cell death, known as apoptosis, which causes tissue injury. Cells that survive may sustain mutations, contributing to the agent’s carcinogenic properties. Although molecular damage begins immediately, physical symptoms do not appear right away. This latent period, lasting one to 24 hours, occurs because visible injury only manifests after damaged cells fail to divide, resulting in tissue separation and blistering.
Immediate Effects on Contact Surfaces
Eye exposure to mustard gas vapor often leads to the most rapid onset of symptoms, typically beginning with intense irritation, pain, and excessive tearing (lacrimation). The delicate tissues of the eye swell rapidly, causing conjunctivitis and painful involuntary twitching of the eyelids (blepharospasm). Severe exposure can lead to corneal damage, resulting in sensitivity to light (photophobia) and temporary blindness within 12 hours.
Skin contact, whether with liquid or vapor, is often initially painless, leading to continued exposure and delayed recognition. The first sign is usually a patchy redness (erythema) developing within a few hours, accompanied by intense itching. Over the next four to 24 hours, this redness progresses to the formation of large, fluid-filled blisters (vesication) that resemble severe thermal burns. Moist areas of the body, such as the armpits, groin, and face, are the most susceptible to severe blistering.
These blisters are slow to heal and highly vulnerable to secondary infection, complicating recovery. Liquid mustard contact is more likely to cause second or third-degree-like chemical burns, while vapor exposure results in first or second-degree injuries. The blistering is a direct result of the agent’s destruction of the basal cell layer, causing the separation of the upper layers of skin. The severity of the skin damage is proportional to the dose, the duration of contact, and the environment’s temperature.
Severe Damage to the Respiratory System
Inhaling mustard gas vapor often causes the most life-threatening injuries, as the agent attacks the internal lining of the airways. Early symptoms are often mild, presenting as a sore throat, hoarseness, and a persistent cough, which can mimic a common respiratory infection. However, the chemical exposure causes severe inflammation and destruction of the epithelial cells lining the trachea and bronchi, a condition known as tracheobronchitis. This damage progresses over several days, leading to chest tightness and significant pain upon coughing.
In severe cases, the damaged lining of the airways begins to slough off, forming thick, sticky sheets called pseudomembranes. These membranes can detach and obstruct the smaller airways, severely impeding breathing and potentially leading to asphyxiation. Inflammation and capillary damage can also cause fluid to leak into the lungs, resulting in pulmonary edema. The destruction of the respiratory tract’s natural protective barrier leaves the lungs extremely susceptible to bacterial infection.
The resulting bronchopneumonia is a common and often fatal complication in the days and weeks following severe exposure. Pulmonary injury is considered the principal cause of death in the acute phase of mustard gas poisoning. Even in non-fatal cases, the long-term scarring and tissue remodeling can lead to chronic respiratory illnesses.
Systemic and Delayed Health Consequences
Once absorbed through the skin or lungs, sulfur mustard enters the bloodstream, causing systemic damage by targeting rapidly dividing cells. The bone marrow is particularly susceptible to the alkylating action, resulting in myelosuppression (suppression of blood cell production). This leads to a decrease in white blood cells (leukopenia), which severely compromises the immune system and makes the victim vulnerable to life-threatening infections and septicemia.
The lining of the gastrointestinal tract, another area of rapid cell turnover, is also vulnerable. Systemic absorption can cause chemical burns to the digestive system, leading to symptoms like nausea, vomiting, abdominal pain, and bloody diarrhea. Neurological symptoms, such as insomnia and hyperexcitability, have been reported in cases of high-dose exposure.
The long-term effects can persist for decades, with chronic respiratory disease being the most common outcome. Survivors frequently develop conditions such as chronic bronchitis, bronchiectasis, and pulmonary fibrosis. Sulfur mustard is also classified as a human carcinogen due to its DNA-damaging properties, increasing the risk of developing lung and skin cancers many years after exposure.
Emergency Response and Medical Management
Immediate and rapid decontamination is the most important step following exposure to limit the amount of chemical absorbed. This involves the quick removal of all contaminated clothing, preferably by cutting it off to avoid dragging it over the skin. Exposed skin should then be washed thoroughly with soap and lukewarm water for at least 10 to 15 minutes. For ocular exposure, the eyes must be continuously flushed with water for the same duration to irrigate the chemical away from the delicate tissues.
Medical management is entirely supportive, as there is no specific antidote to reverse the effects of sulfur mustard once it has reacted with the body’s cells. Treatment focuses on managing symptoms and preventing complications, starting with aggressive pain management for chemical burns. Blisters are often unroofed and treated with antibiotic ointments, such as silver sulfadiazine, to prevent severe secondary infections.
Patients with respiratory distress require intensive care, which may include intubation and mechanical ventilation to maintain oxygenation. Bone marrow suppression is addressed with blood transfusions and growth factors to stimulate the production of new blood cells. The overall prognosis depends heavily on the concentration of the exposure and the speed of the initial decontamination.