Carbon monoxide (CO) is widely known as the “silent killer” because this gas is colorless, odorless, and highly toxic, interfering with the blood’s ability to carry oxygen. When combustion appliances malfunction, CO levels can rapidly become dangerous in enclosed spaces. Do houseplants possess the ability to absorb or neutralize this deadly gas? While plants interact with carbon monoxide, scientific evidence confirms their capacity is far too limited to serve as a practical defense or safety measure against CO poisoning in a home environment.
How Plants Interact with Carbon Monoxide
Plants possess a biological mechanism to process carbon monoxide, though it differs significantly from their uptake of carbon dioxide (CO2). Like all atmospheric gases, CO enters the plant leaf primarily through tiny pores called stomata, which are the gateways for gas exchange. Once inside the leaf tissue, the plant does not use CO as a primary energy source like it uses CO2 for photosynthesis.
Instead, the absorbed carbon monoxide undergoes a metabolic process where it is oxidized, or broken down, into carbon dioxide. This newly formed CO2 can then enter the photosynthetic cycle, or the carbon atom from the CO can be reduced and incorporated into complex organic molecules, such as the amino acid serine. This detoxification process is highly dependent on specialized plant enzymes, like carbon monoxide dehydrogenase, and can occur in both light and dark conditions.
This metabolic activity confirms that plants can process carbon monoxide, but the rate of absorption is extremely low at typical CO concentrations found in ambient air. The plant’s reliance on passive diffusion through the stomata means its ability to remove the gas is constrained by temperature, light, and the opening and closing of these pores. This slow removal is insufficient to counteract the rapid accumulation of CO that occurs during a combustion appliance failure.
The Reality of Indoor Air Purification
The idea that houseplants can purify indoor air gained significant public attention following the 1989 NASA Clean Air Study. This research demonstrated that plants could effectively remove certain pollutants in sealed test chambers. However, the study did not fully explore the effectiveness of plants against dangerous concentrations of carbon monoxide, and the tightly controlled laboratory environment is fundamentally different from a typical home or office building.
The major difference is the high rate of air exchange in a normal building, where fresh air constantly replaces indoor air, rapidly diluting pollutants. To achieve the same air purification rate provided by a standard air exchange in a home, a consumer would need an impractical number of plants, often estimated to be in the hundreds per average-sized room. The volume of air that needs to be processed by plants to reduce a CO threat to a safe concentration is enormous, making plants an unreliable measure for life safety.
The primary risk of carbon monoxide comes from its ability to quickly reach toxic concentrations that can incapacitate a person before they recognize the danger. Because a plant’s CO absorption rate is slow and not a substitute for mechanical ventilation, safety organizations stress that a functioning, regularly tested carbon monoxide detector is the only reliable way to protect against CO poisoning. Placing a houseplant near a CO source offers a false sense of security and cannot be considered a mitigation strategy for this serious hazard.
The Role of Other Common Indoor Pollutants
While plants are not a practical solution for carbon monoxide, they are measurably more effective at mitigating other common indoor air quality issues. Plants absorb and break down Volatile Organic Compounds (VOCs), which are gases emitted from household items like paints, furniture, cleaning products, and building materials. Examples of these VOCs include formaldehyde, benzene, and trichloroethylene.
The removal of these organic chemicals occurs through a dual process involving both the plant’s leaves and the root-soil system. The leaves absorb the VOCs through the stomata, where they are metabolized by the plant tissue. A significant portion of the air-cleaning action takes place in the soil, where microorganisms associated with the plant’s roots break down the pollutants.
This combined leaf and soil ecosystem transforms the VOCs into harmless substances like carbon dioxide, water, and new plant biomass. Common houseplants such as the Snake Plant and Peace Lily have demonstrated effectiveness in reducing the concentration of these organic toxins in laboratory settings. While the practical impact of a few plants in a well-ventilated home is still limited, their measurable effect on VOCs provides a clear benefit distinct from their minimal role in carbon monoxide removal.