Breathing in sewage gases and aerosols poses real health risks, ranging from acute poisoning by hydrogen sulfide to chronic respiratory damage from inhaling bacteria, endotoxins, and viruses that become airborne wherever sewage is exposed to open air. The dangers are not limited to workers descending into manholes. People living near wastewater treatment plants, residents with faulty plumbing, and communities downwind of sewage-contaminated waterways can all be affected. The nature and severity of the harm depends on what you are breathing, how much of it reaches your lungs, and how long the exposure lasts.
The Immediate Danger of Hydrogen Sulfide
The most acutely dangerous component of sewer gas is hydrogen sulfide, the compound responsible for the signature rotten-egg smell. At low concentrations, it is an irritant. At higher concentrations, it becomes a killer. Hydrogen sulfide interferes with the body’s ability to use oxygen at the cellular level; once inhaled, the non-oxidized portion circulates in the blood in dissolved and protein-bound forms that directly contribute to toxicity.1Journal of Medical Toxicology. Hydrogen Sulfide Toxicity: Mechanism of Action, Clinical Presentation, and Countermeasure Development What makes this gas especially treacherous is that it paralyzes the olfactory nerve at dangerous concentrations, meaning the warning smell disappears right when you need it most. People assume they are safe because they can no longer smell anything, when in fact the opposite is true.
Fatalities from hydrogen sulfide in sewers are well documented. A case report of two surveyors working near a manhole described how both fell into the sewer and died from sudden hydrogen sulfide exposure, illustrating the unpredictability of encountering lethal concentrations in confined spaces.2The American Journal of Forensic Medicine and Pathology. Death by Sewer Gas: Case Report of a Double Fatality and Review of the Literature These deaths tend to happen fast and often claim would-be rescuers too, because bystanders rush in without realizing the air itself is the hazard.
Bacteria That Ride the Air
Sewage is teeming with microorganisms, and many of them do not stay in the water. Wherever sewage is agitated, whether by mechanical aerators, bubbling aeration tanks, or even toilet flushes, tiny droplets become airborne and carry bacteria with them. A study of South African wastewater treatment plants identified 36 potential airborne pathogens in the bioaerosol samples, spanning 22 genera. The most abundant included Bacillus, Enterococcus, Clostridium, Streptococcus, Acinetobacter, Pseudomonas, and Escherichia/Shigella.3Scientific Reports. Opportunistic bacterial pathogens in bioaerosols emitted at municipal wastewater treatment plants, South Africa These are not obscure laboratory curiosities. Many are opportunistic pathogens capable of causing infections in people whose immune defenses are compromised, or in anyone who inhales enough of them.
The bacterial load is not just about live pathogens. Endotoxins, fragments of bacterial cell walls from gram-negative bacteria, trigger inflammation even when the bacteria themselves are dead. A cohort study of wastewater treatment plant workers found a positive association between endotoxin exposure and elevated levels of inflammatory markers in the blood, suggesting that daily exposure to these compounds chips away at workers’ health over time.4Water Research. A cohort study of wastewater treatment plant workers: Association between levels of biomarkers of systemic inflammation and exposure to bacteria and fungi, and endotoxin as measured using two methods
Viruses in the Mist
Bacteria are not the only biological hitchhikers in sewage aerosols. Viruses survive aerosolization surprisingly well, and several that cause human illness have been detected in the air around wastewater facilities. Adenovirus was found in 100% of summer air samples and 97% of winter samples at French wastewater treatment plants, with the highest concentrations measured during warmer months.5PubMed. Assessment of airborne virus contamination in wastewater treatment plants Another study of rural wastewater systems detected human-associated caliciviruses in aerosols, along with hepatitis E virus, astrovirus, and norovirus across collection, treatment, and discharge stages.6Journal of Cleaner Production. Occurrence, variation and risks of viruses in aerosols during rural wastewater collection, treatment and discharge
This airborne viral pathway gained attention during the COVID-19 pandemic, when outbreaks in high-rise buildings were linked to viral aerosols traveling through sewer stacks. Failed water traps in plumbing allowed contaminated air from the sewer system to enter apartments, creating a fecal-aerosol-inhalation transmission route.7PubMed Central. Vertical outbreak of COVID-19 in high-rise buildings: The role of sewer stacks and prevention measures The lesson here extends beyond any single virus: wherever plumbing seals fail, the boundary between sewer air and indoor air disappears.
What Happens to the Lungs Over Time
For people exposed to sewage aerosols repeatedly, the respiratory damage tends to be cumulative rather than dramatic. A study of sewage workers found statistically significant decreases in several measures of lung function, including peak expiratory flow and forced expiratory volume. The researchers also found elevated markers of oxidative stress, suggesting that exposure to the dust, fumes, and bioaerosols in sewage work was driving damage through oxidation of lung tissue, contributing to an obstructive pattern of impairment.8PubMed Central. Occupational Health Hazards among Sewage Workers: Oxidative Stress and Deranged Lung Functions
Asthma appears more frequently in sewage workers than in comparable municipal employees. One study found that sewage workers had roughly five times the odds of reporting adult-onset asthma compared to referents, even after accounting for age, gender, allergic history, and smoking.9Journal of Occupational Health. Self-Reported Asthma and Respiratory Symptoms in Sewage Workers A separate analysis of sewage and compost workers found that exposed workers had higher blood levels of fibrinogen and C-reactive protein, classic markers of low-grade systemic inflammation, along with elevated ICAM-1 linked to dust and bacterial exposure.10PubMed. Biomarkers of inflammation in workers exposed to compost and sewage dust
Another study specifically linked hydrogen sulfide and endotoxin exposure among sewer-network and treatment-plant workers to reduced lung function and elevated C-reactive protein, reinforcing the picture of chronic, low-grade inflammation eating away at respiratory capacity.11Annals of Work Exposures and Health. Endotoxin and Hydrogen Sulphide Exposure and Effects on the Airways Among Waste Water Workers in Sewage Treatment Plants and Sewer Net System
It is worth noting that these effects are not inevitable. A prospective study of garbage and wastewater workers in a setting with good working conditions found no significant effects of occupational bioaerosol exposure on symptoms, lung function, or lung-specific proteins.12Occupational and Environmental Medicine. Exposure to bioaerosols, respiratory health and lung-specific proteins: a prospective study in garbage and wastewater workers Protective equipment, ventilation, and modern plant design can make a real difference. The harm is not a fixed property of sewage; it is a function of how much uncontrolled exposure actually reaches the lungs.
Risks for People Living Nearby
You do not need to work in a sewer to be affected. Residents living near wastewater treatment plants have reported higher rates of headaches, unusual tiredness, and difficulty concentrating, along with increased rates of respiratory and skin complaints.13PubMed Central. Impact on the Quality of Life When Living Close to a Municipal Wastewater Treatment Plant People living within about a kilometer of sites where treated sewage sludge was applied to land reported irritation including skin rashes and burning of the eyes, throat, and lungs after winds blew from the treated fields.14PubMed Central. Interactions of pathogens and irritant chemicals in land-applied sewage sludges (biosolids)
Indoor exposure is another overlooked route. Sewer gas can enter homes through dried-out drain traps, cracked pipes, or faulty vent stacks. One investigation found that vapors from a sanitary sewer pipe inside a residence were a source of tetrachloroethylene, a dry-cleaning solvent classified as a likely carcinogen, detected in the home’s indoor air.15PubMed Central. Sewer Gas: An Indoor Air Source of PCE to Consider During Vapor Intrusion Investigations This illustrates that sewer gas is not just hydrogen sulfide and bacteria; it is a vehicle for whatever chemicals have been flushed into the system. Flooding events compound the risk. People with existing respiratory conditions like COPD or asthma face heightened danger from aerosolized pathogens during indoor sewage flooding and the mold growth that follows.16Environmental Impact Assessment Review. Assessing human health risks associated with wastewater flooding
Sewage Biosolids and Infection Risk
When treated sewage sludge, often called biosolids, is spread on agricultural land, bacteria and viruses become airborne in the dust and spray. Estimates of the occupational infection risk from bioaerosols generated during land application fall in the range of about 1 to 2% per year under typical conditions, but extraordinary exposure scenarios push the estimated annual risk as high as 34%, with viruses posing the greatest threat.17PubMed. Estimated occupational risk from bioaerosols generated during land application of class B biosolids The inclusion of norovirus in risk models increases the estimated probability of infection for the general public by over two orders of magnitude compared to models that only consider enteroviruses.18PubMed. Toward a consensus view on the infectious risks associated with land application of sewage sludge This is a serious gap, because norovirus is extremely common in sewage and notoriously infectious at low doses.
Antibiotic Resistance Genes Go Airborne
One of the more alarming discoveries in recent sewage aerosol research involves antibiotic resistance genes. These are stretches of bacterial DNA that encode the ability to survive antibiotic treatment, and they can be transferred between bacterial species. When sewage is aerated, these genes become concentrated in the fine particles that drift into the surrounding air. Studies have detected genes conferring resistance to commonly used antibiotics in air samples collected from screen rooms, sludge thickening basins, and biological reaction basins at treatment plants.19Atmospheric Environment. Bioaerosol emissions and detection of airborne antibiotic resistance genes from a wastewater treatment plant
The enrichment effect is striking. Research on aeration tanks found that the concentration of antibiotic resistance genes in the fine particulate matter above the tanks was roughly 60% higher than in the wastewater itself, driven by foam-forming bacteria with high atomization capability that preferentially launch into the air during bubble bursts.20PubMed. Unveiling the role of aeration tanks in the emission and enrichment of airborne antibiotic resistance genes in a wastewater treatment plant A broader spatial analysis found that wastewater treatment plants contributed over 57% of the clinically relevant antibiotic resistance genes found in fine particulate matter in nearby urban areas, while accounting for only about 11 to 13% of the total bacteria.21PubMed. Inhalable Antibiotic Resistome from Wastewater Treatment Plants to Urban Areas: Bacterial Hosts, Dissemination Risks, and Source Contributions In practical terms, sewage treatment plants appear to be disproportionately seeding the air with the genetic material that makes infections harder to treat.
When the Smell Itself Feels Like the Problem
Not every symptom triggered by sewage odor is caused by chemical toxicity. Research on communities near hazardous waste sites has found that the sulfur compounds in sewer gas, including hydrogen sulfide and mercaptans, have odor thresholds far below the concentrations known to cause direct toxic effects. Yet people who detect these odors frequently report headaches, nausea, and other symptoms. The evidence suggests that odors can serve as a sensory cue that activates stress-related and autonomic responses, especially in people who are anxious about their environmental exposure.22PubMed Central. Symptom prevalence and odor-worry interaction near hazardous waste sites Environmental odors can also exacerbate underlying medical conditions through innate aversion responses and conditioning.23PubMed. Critical review: the health significance of environmental odor pollution
This does not mean people are imagining their symptoms. The symptoms are real, but they arise partly from a neurological stress response to the odor rather than exclusively from the chemicals themselves. For someone living near a sewage facility, the distinction between “the smell is making me sick” and “the chemicals in the smell are poisoning me” is academic in a way that does not help much. The headaches are still headaches. But it does mean that at very low concentrations, the smell of sewage can make you feel ill without necessarily causing organ damage, while at higher concentrations, the chemicals cause direct harm regardless of whether you are worried about them.
Microplastics and Chemical Contaminants in Sewage Aerosols
The list of things that become airborne from sewage keeps growing. Microplastics have been found in aerosols at every stage of wastewater treatment, at concentrations ranging from roughly 1 to 28 particles per cubic meter of air, with 30 different polymer types identified. The dominant size range was 20 to 50 micrometers, small enough to be inhaled deep into the lungs.24PubMed. Aerosols Generated in the Wastewater Treatment Process Are a Potential Source of Airborne Microplastics Indoor environments at sewage-handling facilities concentrate these particles further; one study found indoor microplastic counts many times higher than outdoor air, peaking near sludge dryers and conveyors where workers spend their shifts.25PubMed. From waste to workplace: Airborne microplastics and endotoxins in an indoor industrial environment
Even more unexpected is the discovery that pharmaceutical compounds, personal-care-product chemicals, and illicit drug residues in sewage can become aerosolized in coastal settings. Using a cocaine metabolite as a sewage tracer, researchers demonstrated that wastewater compounds, including methamphetamine, tire chemicals, and the sunscreen ingredient octinoxate, were detectable in aerosols near the Tijuana River, potentially exposing nearby populations to tens of nanograms per hour of these substances through inhalation.26PubMed Central. Identifying wastewater chemicals in coastal aerosols The long-term health implications of chronically inhaling a low-dose cocktail of pharmaceuticals and industrial chemicals are still largely unknown, but the exposure pathway itself is no longer in doubt.
A Fear That Was Right for the Wrong Reasons
Americans spent roughly forty years, from 1870 to 1910, in genuine terror of sewer gas, blaming it for diseases ranging from typhoid to diphtheria. The rise of germ theory eventually dismantled the miasma framework, and “sewer gas” fell from its position as the boogeyman of public health.27PubMed Central. Constructing and dismantling frameworks of disease etiology: the rise and fall of sewer gas in America, 1870-1910 The irony is that Victorian-era fears were not entirely unfounded. They got the mechanism wrong, attributing disease to foul vapors rather than to specific pathogens, but the intuition that breathing air contaminated by sewage could make you sick turns out to be correct in ways they could not have imagined. The bioaerosol research of the past two decades has essentially validated the old anxiety with modern evidence: the air above sewage really does carry bacteria, viruses, endotoxins, antibiotic resistance genes, microplastics, and volatile chemicals, and inhaling them really can cause harm.
What Protection Actually Helps
For workers entering confined sewer spaces, the non-negotiable first step is atmospheric monitoring before entry. Portable gas detectors that measure hydrogen sulfide, methane, oxygen depletion, and volatile organic compounds are standard equipment in professional sewer work. Respiratory protection matters too: research on bioaerosol filtration has shown that HEPA and N95 filters provide a meaningfully higher level of protection against microbial particles than basic dust-mist filters.28PubMed Central. Respiratory protection against bioaerosols: literature review and research needs For high-risk tasks like cleaning aeration tanks or entering enclosed pump stations, supplied-air respirators eliminate the filtration question entirely by giving the worker a separate air supply.
For people at home, the most important defense is functional plumbing. Water traps in drains exist specifically to block sewer gas from entering living spaces, but they dry out in seldom-used bathrooms, floor drains, and vacant units. Running water through every drain in your home every few weeks keeps those traps sealed. Cracked or disconnected vent pipes in walls or attics are harder to detect but can channel sewer gas directly into living areas. If you smell rotten eggs indoors without an obvious source, a plumber checking vent stacks and trap seals is a better investment than an air freshener. Sewage backups during flooding events warrant aggressive ventilation and, for people with respiratory conditions, temporary relocation until the space can be properly dried and cleaned.