Respiratory Health with Dusty & Moldy Grain

Respiratory Health with Dusty & Moldy Grain
By: John Shutske, Damon Smith, Steve Kirkhorn, and Paul Esker
(Author affiliations at end of article)

If you produce corn, soybeans, or other crops in the Midwest, being exposed to dust while you are working is inevitable. Breathing grain dust can affect the health and overall comfort for grain producers and others who work in the grain industry. Exposures can occur:

  • In the combine
  • While unloading
  • During drying and processing
  • In bins
  • While grinding/mixing grain and other feed products (including hay and silage)
Grain dust is a complex soup made up of both organic and inorganic particles. Some particles can be inhaled easily, and depending on their size, dust can find its way deep into the respiratory system and cause a range of negative health effects. Smaller particles are generally more harmful because they can find their way more deeply into the lungs. Grain dust is biologically active, and is made up of:

  • Plant material
  • Mold and mold spores
  • Insect parts and excreta
  • Bacteria
  • Endotoxins (toxins contained in the cell walls of some bacteria)
  • Soil

Exposure to Small Concentrations During Normal Work

Most people will have some reaction to dusty conditions during harvest. Often, this will be a nuisance reaction (like a runny nose) or irritation, but in some cases, bigger health problems are possible. Even in the cab of a combine, there is some dust (1 to 15 mg of dust per cubic meter). Also endotoxins (even with a sealed cab and proper air filtration) can reach limits that cause symptoms for some individuals. At low dust levels that a healthy person might routinely encounter during harvest operations, developing a cough is common. This might be an intermittent cough, often producing more phlegm when actual work is happening around dust. Other common symptoms are:

  • Chest tightness and/or wheezing
  • Sore/irritated throat
  • Nasal and eye irritation
  • Feeling of being stuffed-up and congested

Chronic or acute bronchitis is common for those who handle grain as the main lung passages get inflamed. Grain dust can also be a significant and limiting problem for those with asthma.

Exposure to Higher Concentrations of Grain Dust

Higher concentrations of dust exposure like you might encounter close to a combine in operation, in a bin, or while unloading or processing grain are a concern especially in years where there are higher levels of mold present or when you have lower quality grain that might be more dusty and prone to damage.  

Moldy, damaged, dusty grain can cause significant health issues for people. For many individuals, a heavy dose of dust even for a short time period can lead to symptoms that occur a few (2 to 6) hours after exposure and may noticeable after they’ve gone home at night. These symptoms from a heavy dose of grain dust exposure can include:

  • Cough
  • Chest tightness
  • Malaise-general feeling of discomfort, illness, or feeling “ill-at-ease”
  • Headache
  • Muscle aches
  • Fever

Why People React This Way to a “Massive” Exposure to Moldy Grain

Most people who have worked around grain will occasionally find themselves in the midst of a space that is obviously very dusty. This “massive” exposure to a cloud of dust for several minutes or hours is something that should be avoided. Though, total avoidance might not always be possible or practical. A massive exposure to moldy, dusty grain even for a short period of time can result in two distinct medical conditions. These conditions are also common when exposed to dusty or moldy hay and silage. The two common conditions look VERY similar and have the same cluster of symptoms outlined above (cough, chest tightness, etc.) but they are actually quite medically different. These two conditions are “Farmer’s Lung” or Farmer’s Hypersensitivity Pneumonitis (FHP) and Organic Dust Toxic Syndrome (ODTS).

“Farmer’s Lung” or Farmer’s Hypersensitivity Pneumonitis (FHP) is relatively less common and generally affects about 1 in 20 exposed individuals. Many times farmers tell their health provider about their symptoms and the reaction sometimes gets mislabeled as FHP. However, FHP is a delayed allergic reaction caused when highly sensitive people breathe in grain dusts causing their bodies to produce “antibodies” as a reaction to the dust. Since FHP is an allergic reaction and involves the body’s immune system, repeated exposures and bouts with FHP often get worse with each exposure. Some individuals may become physically unable to work in dusty areas and can develop permanent lung damage through repeated exposures.

Farmer’s Hypersensitivity Pneumonitis is most often brought on or made worse by dust that contains mold, mold spores, and bacteria that had developed under warm/hot storage conditions. These heat-loving organisms are actually more likely to grow in stored hay or sometimes in the top layers of stored silage as compared to grain that was standing out in the field, though exposures that lead to FHP can occur from grain including stored grain. If you’ve been diagnosed with FHP before, and get sick in the future while working around grain (or hay/silage), it is a good idea to see your family doctor.

“Organic Dust Toxic Syndrome” or ODTS, as the name suggests, is a toxic reaction as compared to the allergic reaction that causes FHP. The respiratory system can get inflamed from the dust, molds, bacteria, and endotoxins in grain dust. With ODTS, people develop a set of symptoms that look very similar to FHP even though the actual reaction by the body that causes the symptoms is quite different. People who develop ODTS will usually recover in a few days. Permanent lung damage from ODTS is not likely to occur with a single exposure, but the person might feel fairly sick (fever, fatigue, cough, chest tightness, etc.) for a few days after exposure. Again, your family doctor or other health professional should be consulted if you develop this type of reaction. It is possible that repeated occurrences of ODTS can lead to FHP and other allergic reactions in some people, so prevention is important.

A difficult problem is that since Farmer’s Lung (FHP) and Organic Dust Toxic Syndrome (ODTS) have such similar symptoms, it is hard even for health professionals to recognize and know the difference. Additional medical testing will be needed to tell the two apart. Medical treatment is also different. References cited at the end of this article might be helpful for your physician if you visit your doctor’s office with serious problems that you think might be connected to harvesting or handling dusty and moldy grain. 

Another concern in the late fall is that respiratory symptoms that result from grain dust exposure can look much like seasonal influenza. If you’ve been working in dusty conditions and end up with a “flu-like illness,” make sure you let your healthcare provider know you’ve had significant dust exposures. Influenza is a viral illness and is treated in a different manner from either FHP or ODTS.

Controlling Exposure Risks

Grain dust exposure and the associated problems and health symptoms are complex. Here are some specific things you can do to control your risk:

  • Have the correct and clean air filter in place when operating a grain combine. Use the appropriate setting on the blower in the cab whether you are using the heater or the A/C. This will minimize dust concentrations in the cab by creating slight pressure inside the operator’s station. When replacing cab air filters, make sure gaskets are intact and installed correctly and that the air is being well-filtered.
  • Avoid direct exposures to dust whenever possible, regardless of your sensitivity. Stay in the cab with the door closed when unloading. If you’re outside unloading or moving grain in other ways, use the wind to your advantage rather that standing directly in a cloud of dust any time grain is being moved.
  • Properly adjust your combine to minimize grain damage. This will help to also minimize the amount of dust being generated. Properly harvested grain will also store better and for longer periods of time with fewer mold and insect issues.
  • Wear a NIOSH-approved and certified “N-95” dust mask (respirator) that fits your face properly. This is especially critical if you find yourself working in a very dusty situation that cannot be avoided. CAUTION: Wear a respirator only if you are free of health problems, particularly with your heart and lungs. Respirators are only effective if you are cleanly shaven. Local health professionals can be a great source of information and can recommend the type of respirator that can be safely worn if a person has any underlying medical conditions including cardiac and respiratory conditions.  If you have a beard or need extra protection, a powered air purifying respirator (PAPR) also commonly known as an “air helmet” can be used in these situations. If you work in a facility where worker safety regulations for respiratory protection apply (such as a grain elevator or feed mill), there are other mandated regulatory requirements before a dust mask or other type of respirator can be worn by workers.
  • Avoid dust exposure if you have any chronic respiratory health issues, including asthma, previous experience with Farmer’s Hypersensitivity Pneumonitis, or existing respiratory infections or conditions. Individuals who have these conditions should be alert for symptoms, even when working in a relatively clean environment like the cab of a combine, and should minimize their exposure to dust.
  • If you feel sick, call your health care provider. If you find yourself working in a very dusty situation (like loading or cleaning out a bin or getting a heavy, prolonged exposure near a combine in the field) and end up feeling sick a few hours later, call for medical advice. Again, your problem may be a condition like ODTS or FHP, but you may also have seasonal influenza or another illness.
  • Smoking tends to make any type of symptoms or reaction caused by dust exposure much worse. Realize that smoking increases the risk of developing respiratory diseases such as emphysema and chronic bronchitis.


John Shutske, PhD and Damon Smith, PhD,  UW-Extension, Cooperative Extension and UW-Madison, College of Agricultural and Life Sciences

Paul Esker, PhD, University of Costa Rica, San José, Science Education, Mathematics Education, Plant Protection and Animal Health.

Steve Kirkhorn, MD, Former Medical Director, National Farm Medicine Center – Marshfield Clinic


  1. Kirkhorn SR. Agricultural Respiratory Health in Critical Need. Partners in Agricultural Health. Wisconsin Office of Rural Health. Available at:
  2. Donham, K. J., & Thelin, A. (2006). Agricultural medicine: occupational and environmental health for the health professions. Wiley-Blackwell. (Chapter 3 contains information that can help a health professional differentiate between Farmer’s Hypersensitivity Pneumonitis and ODTS).
  3. Girard, M., Lacasse, Y., & Cormier, Y. (2009). Hypersensitivity pneumonitis. Allergy, 64(3), 322-334.
  4. Kirkhorn, S. R., & Garry, V. F. (2000). Agricultural lung diseases. Environmental health perspectives, 108(Suppl 4), 705.
  5. Seifert, S. A., Essen, S. V., Jacobitz, K., Crouch, R., & Lintner, C. P. (2003). Organic Dust Toxic Syndrome: A Review: REVIEW. Journal of Toxicology: Clinical Toxicology, 41(2), 185-193.

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