Mustard gas attacks nearly every tissue it touches, but the damage starts at the molecular level: it chemically binds to DNA and proteins in your cells, disrupting their ability to function and reproduce. The effects hit skin, eyes, and lungs hardest because those are the surfaces the oily liquid or vapor contacts first. What makes mustard gas uniquely cruel is that symptoms are delayed by hours, so victims often absorb a damaging dose before they even realize they’ve been exposed. And the harm doesn’t end when the acute burns heal. Decades later, survivors can develop progressive lung disease, blindness, and cancer linked to that single encounter.
How It Damages Cells
Sulfur mustard, the chemical behind mustard gas, is what toxicologists call a bifunctional alkylating agent. In plain terms, the molecule has two reactive arms, each capable of latching onto a strand of DNA. When both arms grab hold, they can stitch two DNA strands together in a way that blocks the cell from reading its own genetic instructions or dividing normally. This cross-linking of DNA is the root cause of most of the downstream destruction.
The alkylation isn’t limited to DNA. The molecule also attacks proteins and other large molecules inside and between cells. One consequence is the activation of a cellular repair enzyme called PARP, which burns through a cell’s energy reserves (ATP) as it tries to fix the damage. At higher concentrations, this energy crash is so severe that the cell dies outright through necrosis, an uncontrolled form of cell death that spills inflammatory contents into surrounding tissue and amplifies the injury.
Skin Blistering and Burns
The signature wound of mustard gas exposure is the blister. Large, fluid-filled blisters can appear anywhere the liquid or concentrated vapor contacts the skin, though moist areas like the groin, armpits, and neck are especially vulnerable because the agent dissolves readily there. Blistering typically begins four to twelve hours after contact, sometimes longer, which is part of why the weapon is so dangerous: soldiers or civilians in a contaminated zone may not seek shelter or decontaminate in time.
The blisters form because mustard gas attacks the thin layer of adhesive proteins anchoring the outer skin (epidermis) to the deeper layer (dermis). Specifically, the agent alkylates adhesive molecules in the basement membrane zone, weakening the bond between the two layers until they separate, much like wallpaper lifting off a damp wall. Fluid from the dermis floods into the gap, producing the characteristic vesicle.
Long after those acute blisters resolve, survivors often deal with chronic skin problems. Persistent dryness, abnormal pigmentation (patches that are either lighter or darker than surrounding skin), and scarring are common among people exposed decades earlier. In rare cases, long-term skin changes progress to skin cancer.
What Happens to the Eyes
The eyes are extraordinarily sensitive to mustard gas. Even vapor concentrations too low to blister skin can cause intense eye irritation. Acute symptoms include tearing, a gritty burning sensation, swelling of the eyelids, and blurred vision. In more severe exposures, the cornea develops microblisters at the junction between its surface layer and the underlying tissue, mirroring the skin’s epidermal-dermal separation but on a much smaller scale. When enough of these microblisters coalesce, the corneal surface layer sloughs off entirely, an agonizing injury that can lead to scarring and vision loss.
What catches many people off guard is that eye problems can resurface years or even decades after an apparently healed initial injury. This phenomenon, known as delayed-onset mustard gas keratopathy, involves progressive corneal clouding, new blood vessel growth into the normally clear cornea, and loss of the stem cells that normally regenerate the corneal surface. Reports from Iranian veterans of the Iran-Iraq War document delayed eye complications appearing as late as 40 years after the original exposure, with most surfacing 10 to 15 years out. The condition can progress to functional blindness if untreated.
One surgical approach that has shown promise for these delayed cases is keratolimbal allograft, a procedure that transplants healthy stem cells from a donor’s cornea to restore the damaged surface. Studies on Iranian veterans with limbal stem cell deficiency from mustard gas found that this technique, sometimes combined with corneal transplantation, produced durable and visually acceptable results. But the procedure requires long-term immunosuppressive therapy, and not all patients are candidates.
Respiratory Tract Damage
Inhaling mustard gas vapor or aerosol damages the entire airway, from the nose and throat down to the smallest branches of the lungs. In the first hours and days, victims experience a burning sensation in the throat, hoarseness, cough, and a feeling of chest tightness. More severely exposed individuals develop full-blown acute respiratory distress syndrome, a life-threatening condition in which the lungs fill with inflammatory fluid and can no longer exchange oxygen efficiently.
At the tissue level, the inhaled agent triggers DNA damage, cell death, and a flood of inflammatory signals in the airway lining. Immune cells pile into the respiratory tract, and the resulting inflammation can narrow or obstruct the airways. This acute phase can be fatal on its own, but survivors face a separate set of chronic problems. Over months and years, the injured airways remodel themselves in ways that progressively restrict airflow. Two patterns dominate: bronchiolitis obliterans, in which scar tissue plugs the small airways, and pulmonary fibrosis, in which the lung tissue itself stiffens with excess collagen. Both conditions worsen over time. Animal studies show that these changes develop gradually and continue to progress long after the initial exposure, driven by profibrotic growth factors that the damaged tissue keeps producing.
Among veterans of World War I and the Iran-Iraq War, as well as workers in mustard gas production facilities, chronic bronchitis, emphysema, and obstructive lung disease have been major sources of long-term disability. A 57-year follow-up of Japanese factory workers who produced mustard gas found that mortality from chronic bronchitis and emphysema was nearly five times higher than in the general population.
Bone Marrow Suppression and Blood Cell Collapse
Mustard gas doesn’t need to be inhaled or touch the lungs to cause systemic harm. Even when exposure is limited to the skin, the agent absorbs into the bloodstream and attacks rapidly dividing cells throughout the body. Bone marrow, where blood cells are produced, is especially vulnerable because its cells divide constantly.
In animal models replicating skin-only exposure, a single dose of sulfur mustard caused acute depletion of bone marrow cellularity within five days. Circulating red blood cells dropped by roughly 60%, white blood cells fell about fourfold, and hematocrit (the proportion of blood made up of red cells) dropped by half. This kind of pancytopenia, a simultaneous crash in all major blood cell types, is the principal cause of death in severe mustard gas casualties. Without enough white blood cells, the body can’t fight infection. Without enough red blood cells, tissues are starved of oxygen. Without enough platelets (which drop alongside the others), bleeding becomes uncontrollable.
This bone marrow destruction is what makes moderate-to-severe mustard gas exposure resemble radiation sickness. In fact, it was precisely this observation, that mustard agents profoundly suppress the blood-forming and immune systems, that led researchers in the 1940s to investigate related nitrogen mustard compounds as treatments for lymphoma. The reasoning was straightforward: if the agent destroys rapidly dividing immune cells, maybe it could destroy rapidly dividing cancer cells too. That line of thinking gave rise to mechlorethamine and the broader class of alkylating chemotherapy drugs, making mustard gas research, perversely, the birthplace of modern cancer chemotherapy.
Cancer Risk
The same DNA-damaging properties that make mustard gas acutely destructive also make it a potent carcinogen. The International Agency for Research on Cancer classifies sulfur mustard as a Group 1 carcinogen, meaning there is sufficient evidence that it causes cancer in humans.
The strongest data come from occupational studies of factory workers who produced or handled mustard gas during the World Wars. These populations showed elevated rates of cancers of the respiratory tract (larynx and lung), oral cavity, and skin. In a long-running Japanese cohort study, male workers had roughly double the expected mortality from lung cancer and triple the expected mortality from upper respiratory tract cancer compared to the general population. Workers with the heaviest cumulative exposure had the highest cancer death rates, following a clear dose-response pattern.
The cancer risk doesn’t appear to require chronic occupational exposure, either. Research on veterans exposed during the Iran-Iraq War suggests that even a single battlefield exposure can increase the risk of developing lung cancer later in life. The mechanism is straightforward: the DNA cross-links and mutations caused by sulfur mustard may persist in surviving cells, accumulating additional genetic errors over the years until a cell transforms into a cancer.
Neurological and Psychological Effects
For decades, mustard gas was treated primarily as a skin, eye, and lung toxin. More recently, clinical observations of aging veterans have drawn attention to its effects on the nervous system. Veterans exposed to sulfur mustard during the Iran-Iraq War report higher rates of cognitive decline, depression, anxiety, and apathy compared to unexposed peers. These aren’t simply the psychological scars of wartime trauma. Animal and cell studies have identified direct neurotoxic effects of sulfur mustard, including damage to nerve cells that mirrors the cognitive and emotional symptoms seen in human survivors.
The mechanisms are still being studied, but the picture emerging is that the same alkylating chemistry that damages skin and lung cells also injures neurons and supporting cells in the brain. Whether this neurotoxicity results from direct exposure of nerve tissue, secondary inflammatory damage, or both remains an active area of research.
Reproductive Harm
Another dimension of mustard gas damage that receives less public attention is its effect on fertility and pregnancy outcomes. A retrospective study of Iranian veterans’ families compared pregnancy outcomes between wives of chemically exposed and unexposed veterans. The wives of exposed veterans had significantly higher rates of spontaneous abortion, congenital anomalies in their children, and secondary infertility. The worst outcomes clustered among veterans whose injuries covered more than half their body surface area, suggesting a dose-related effect on reproductive health.
This finding fits what we know about the agent’s mechanism. Because sulfur mustard directly damages DNA, sperm cells carrying mutated genetic material could plausibly lead to developmental problems in offspring. The effect also has precedent in the broader pharmacology of alkylating agents: the chemotherapy drugs descended from nitrogen mustard are well known to impair fertility.
The Decontamination Window
One of the most critical practical facts about mustard gas is that decontamination timing matters enormously. Sulfur mustard begins penetrating skin within minutes of contact. The agent binds to tissue components quickly enough that once symptoms appear, much of the damage is already locked in. This is why military and emergency protocols emphasize removing the agent as fast as possible, ideally within the first few minutes.
Two decontamination approaches have been studied extensively in skin models. Fuller’s earth, a dry absorbent clay, has been used by militaries for decades. Reactive Skin Decontamination Lotion (RSDL) takes a different approach: rather than just absorbing the agent, it chemically neutralizes it on the skin surface. Head-to-head comparisons in both pig models and in vitro human skin studies consistently show that RSDL outperforms Fuller’s earth in reducing skin injury from sulfur mustard, particularly in limiting the inflammation and cellular damage in deeper skin layers. When applied within five minutes of contamination, both products significantly reduce the severity of skin lesions, but RSDL produces statistically better outcomes. Both are far better than doing nothing.
Beyond skin, there is no true antidote for systemic mustard gas poisoning. Treatment is supportive: managing pain, preventing infection of blistered skin, providing respiratory support for lung damage, and in severe cases, treating bone marrow failure with blood transfusions or growth factors. Research into more targeted therapies continues, but no drug currently reverses the DNA alkylation once it has occurred.
Why Contamination Lingers in the Environment
Mustard gas is not just a threat at the moment of release. The compound is relatively stable in soil and can persist in the environment for decades under the right conditions. Its primary breakdown product, thiodiglycol (TDG), is itself persistent and has been detected in soil and groundwater at sites contaminated by mustard gas more than 60 years after the original dumping. Complicating matters, TDG can react with intermediates of mustard gas degradation to regenerate more toxic compounds, effectively reversing the breakdown process.
This environmental persistence is why old munitions dumps, former chemical weapons factories, and World War-era battlefields remain hazardous. Fishermen in the Baltic Sea, where large quantities of chemical weapons were dumped after World War II, have occasionally pulled up corroded shells still containing active mustard agent. Construction workers at former production sites have been accidentally exposed. The soil chemistry that governs how quickly TDG breaks down depends on microbial activity, moisture, temperature, and soil composition, meaning some sites may remain contaminated essentially indefinitely without active remediation.
Why Symptoms Take Hours to Appear
The delayed onset of mustard gas symptoms is one of its most tactically and medically frustrating features. Unlike agents that cause immediate pain on contact, sulfur mustard produces little or no sensation at the time of exposure. The chemical reaction with DNA and proteins begins immediately, but the cellular machinery takes hours to fail. Cells continue functioning for a while even after their DNA has been cross-linked; it is only when they attempt to divide or when the accumulating damage overwhelms repair mechanisms that they begin to die in large numbers. The inflammatory cascade that produces visible blistering, redness, and pain follows the wave of cell death.
This delay has practical consequences beyond the battlefield. In an accidental or terrorist exposure scenario, people who feel fine may leave a contaminated area and unknowingly spread the agent through contaminated clothing, creating secondary exposure risks for family members, bystanders, and first responders. Emergency planning for chemical incidents accounts for this by treating all individuals in a contaminated zone as potentially exposed, regardless of whether they have symptoms yet.
How Survivors Fare Over Decades
The largest population of living mustard gas survivors is the community of Iranian veterans injured during the Iran-Iraq War in the 1980s, numbering in the tens of thousands. Studies following this population have provided the most detailed modern picture of what long-term survival after mustard gas exposure looks like. Beyond the chronic lung disease, eye complications, and skin changes already described, these veterans experience overlapping problems that compound each other. Scarred and narrowed airways make them prone to recurrent respiratory infections. Damaged corneas require repeated surgical interventions. Chronic pain from skin lesions and neuropathy erodes quality of life. The cognitive and emotional symptoms layer on top, and the cumulative burden leads to substantially higher rates of disability than in comparable unexposed veterans.
The Iranian experience has also revealed how unpredictable the timeline of complications can be. Some veterans stabilize after the initial injury and live relatively normal lives for years before a delayed complication surfaces. The 10-to-40-year window for delayed-onset eye disease is one example, but similar late deterioration occurs in the lungs, where stable chronic bronchitis can give way to progressive fibrosis years later. This unpredictability makes lifelong medical monitoring essential for anyone with a history of significant exposure.