What Are Volatile Organic Compounds (VOCs)? Definition, Examples, and How to Avoid Them

VOCs, or volatile organic compounds, are compounds that contain carbon atoms and that, at room temperature, easily evaporate. Too small to see and virtually omnipresent both indoors and out, they can be inhaled in normal breathing.

“Volatile” means that the compound vaporizes. “Organic” in this context means “containing carbon molecules.” While “organic” also usually suggests “naturally occurring,” many VOCs are human-made.

Some VOCs—like the smells emitted by many decorative flowers—are pleasant when inhaled. However, not all VOCs have an associated smell, which means that people cannot always tell that they are breathing them. This is a problem because, while many VOCs are harmless, many are hazardous.

Microbial Volatile Organic Compounds

Microbial volatile organic compounds (mVOCs) are especially small. They include mold as well as other fungi and some bacteria. 

Some mVOCs are often blamed as the cause of “sick house syndrome” and “sick building syndrome.” Health care professionals sometimes use these terms when referring to people with a mix of adverse responses to the structures in which they live or work. Dampness as well as naturally occurring mVOCs like mold and human-made VOCs in construction materials can all play a role in sick house/building syndrome. 

Even though it is not technically an mVOC, the radioactive gas radon is often categorized in public documents with mVOCs because it’s invisible when inhaled and can dangerously contaminate homes and other structures. Produced by the breakdown of uranium in the soil, rock, and water under a building, radon is the leading cause of lung cancer among non-smokers, according to the Environmental Protection Agency (EPA). 

Sources of Human-Made VOCs

Thousands of everyday, human-made products contain VOCs that become gases at room temperature.

Because some VOCs are made accidentally during burning or industrial processes, there are an unknown number of them. Instead of creating ever-lengthening lists of VOCs, the EPA, the American Lung Association, and various research scientists have identified some of the most common human-made sources of dangerous VOCs. 

Indoor Sources

In homes, offices, places of business, health care settings, and factories, common VOC sources can include:

• Natural gas in cooking stoves and fuels used to heat homes
• Cleaning solvents, disinfectants, and air fresheners
• Glues and many arts and crafts materials like permanent markers,
• Paints, paint strippers, varnishes, and lacquers
• Caulks, sealants, and adhesives
• Printers and copy machines
• Carpets and upholstery
• Toys
• Fire extinguishers
• PVC pipes
• Pressed wood products commonly found in low-cost furniture, flooring, and the walls and cabinetry of mobile homes
• Personal care products, cosmetics, and nail polish removers
• Dry-cleaned clothing
• Industrial processes
• Fumigants used to control pests and insects,

Hospitals and healthcare settings are often rich in VOCs because of their heavy reliance on cleaning solutions and disinfectants and because of the plastics used throughout the buildings.

Outdoor Sources

Common outdoor sources include:

• Gasoline
• Diesel exhaust
• Propane and butane in outdoor torches, gas grills, and heaters
• Industrial emissions
• Smoke from fireplaces and woodburning stoves
• Emissions from oil and gas fields
• Agricultural fumigants. 

Outdoors under sunlight, some VOCs bind with larger airborne molecules and contribute significantly to particulate air pollution and ground-level ozone.

Ozone high in the atmosphere shields Earth from harmful ultraviolet rays. Low-lying ozone is another matter altogether. It’s the primary component of smog.

While smog has long been considered both an urban and a warm-weather problem, VOC and nitrogen dioxide emissions from oil and gas fields have created unhealthy concentrations of smog even in rural areas and in cold weather. The fields leak both kinds of pollutants into the air by deliberate venting and flaring, through motor emissions, and through inadvertent seepage during transport.

In addition to the havoc that smog can wreak on human, plant, and animal health, smog contains black carbon particulates that raise temperatures in rain, snowpack, and air. Studies are underway to determine the extent to which smog contributes to global warming. By forcing changes to climate in the Northern Hemisphere, smog may even contribute to arctic amplification and to new, diverging precipitation patterns in Asian monsoons.

Volatile Organic Compounds in Groundwater

According to the United States Geological Survey (USGS), when human-made liquids in surface water like lakes, rivers, and streams contain VOCs, the VOCs tend to evaporate into the air. However, if VOCs end up in groundwater due to an underground storage tank leak, for example, or due to improper disposal, they can enter aquifers. Some VOCs cling to aquifer soil. Bacteria disintegrate some. Even so, a significant amount can end up in drinking-water supplies.

VOCs from chlorinated water and methyl tert-butyl ether (MtBE) are often found in well water. MtBE is a liquid that was added to gasoline. Its use was phased out when scientists realized that it sickens livers and kidneys and causes cancer in lab animals. Even though it is no longer on the market, MtBE is especially persistent in groundwater and water supplies.

Most water that comes from public water supplies is tested for VOCs regularly. Water that’s in private wells can be tested in labs certified to assess concentrations of VOCs. 

How to Avoid Indoor VOCs

VOCs are hard to avoid indoors. Often, they are in building materials and furniture. They are also plentiful in everyday household products. 

The EPA recommends avoiding overexposure to VOCs. The agency's ideas for how to do this include:

• Open windows if possible and if the weather permits.
• Use VOC-containing products only in well-ventilated areas.
• Follow label precautions and even exceed recommendations when possible. 
• Buy paints, paint sealers, glues, varnishes, lacquers, and the like in small quantities and don't store leftovers in opened containers. 
• Safely discard leftover VOC products if you’re not likely to use them. (Many municipalities coordinate special toxic waste collection days.)
• To minimize the off-gassing of formaldehyde, apply a sealant to pressed wood. (Be careful, however, not to use a sealant that is high in VOCs.) The EPA also recommends using an air conditioner and dehumidifier on hot days to slow down the rate of off-gassing.
• Use insect and pest management systems that don’t rely on fumigation. 
• Keep materials containing VOCs out of reach of children and pets.
• Don't mix VOC-containing products unless the labels direct you to do so.

Unfortunately, the EPA cautions that terms like “green,” “eco,” and “environmentally friendly” on product labels are not always reliable indicators of VOC levels. Ditto, unfortunately, for “low VOC,” and “zero VOC.”

In the United States, no national organizations other than the Food and Drug Administration (FDA) regulate VOC labeling, and the FDA only regulates the labels on food, drugs, and personal care products. Some international programs do regulate VOC labeling but they don’t always use standardized norms. 

Air Filters

While HEPA filters work well to capture small, solid airborne particles like dust, pollen, mold, and bacteria, they cannot capture gases. To remove VOCs from indoor air, the EPA recommends the use of portable air cleaners that rely on activated carbon filters. According to the agency, they can remove 95%-99% of VOCs from the air.

Beware of the VOCs in Personal Care Products

Cosmetics, fragrances, and nail polish remover are common sources of many VOCs. Certainly, not all of these are harmful. Some, however, are. For example, while acetone is a naturally occurring chemical that humans make in their bodies, at high doses in personal care products it has known effects on humans’ eyes, skin, respiratory systems, and central nervous systems. Acetone is found in many nail polish removers and lotion-based cosmetics.

The FDA does not have the authority to approve the ingredients in cosmetics, fragrances, and nail polish remover. This means that it doesn’t test them for safety before allowing them in a product. Instead, the agency regulates the ingredients. It does so largely by insisting that all ingredients be plainly listed on product labels.

Even so, the FDA can have difficulty ensuring that products carry useful information on their labels. For example, it cannot demand that manufacturers divulge trade secrets. Because of this, labels are sometimes less than clear. For example, rather than name a specific chemical additive that creates a fragrance and is exclusive to one manufacturer, a product’s label might merely use the generic term, “fragrance.”