Protecting Lung Health Around Moldy Grain, Hay, and Other Products

Dusty conditions are common on farms when working with grain, hay, silage and other products. Recent wet conditions from excess rain and flooding often makes these issues worse especially as products begin to grow mold and deteriorate. In addition, even during normal times, in the fall, Wisconsin producers work feverishly to get crops harvested before the snow flies find themselves exposed to a variety of dusts. Breathing farm dusts can affect your comfort and is a health concern for all in the industry. You can be exposed:

  • When handling, processing or feeding hay and other products
  • During harvest operations such as chopping, baling or running a grain combine
  • Unloading (bins, trucks, wagons, etc.)
  • During drying and processing
  • In bins (filling, emptying and cleanout)
  • Grinding and mixing hay, silage, grain and other feed products

Farm dusts are comprised of a complex soup of particles. The smallest dust particles are easily inhaled and find their way deep into the respiratory system. These dust particles are biologically active. They are made up of:

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

Exposure to Small Concentrations During Normal Work

Most people will have some type of physical reaction to dusty conditions. Often, this will be a nuisance reaction (like a runny nose) or throat irritation. In some cases, bigger health problems occur. Even inside a sealed combine, chopper or tractor cab, there will be some dust. Endotoxins associated with some types of bacteria (even with a sealed cab proper air filtration) can cause problems for some individuals. At low dust levels during prolonged and busy operations (like a week or two of forage or grain harvest), a cough is common. This might be an intermittent cough, producing more phlegm when you’re working near dust. Other symptoms are:

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

Chronic and acute bronchitis is also quite common for those who handle grain frequently. Bronchitis occurs as lung passages get inflamed. Grain dust can also be quite a debilitating concern for those with asthma.

Exposure to Massive Concentrations and Clouds of Dust from Grain or Hay

A “massive” exposure to a thick cloud of dust is something to avoid. Though, total avoidance is not always possible. Massive exposures to moldy, dusty products even for a short period of time can result in two distinct medical conditions having symptoms that include:

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

People exposed often begin to feel sick a few hours after their exposure and may feel quite sick as they go to bed at night.  The two common conditions we might see here in the Midwest 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 less common and affects about 1 in 20 exposed individuals (5% or slightly more). Often, farmers get sick and tell their health provider about their symptoms and their illness sometimes gets misdiagnosed as FHP.

However, FHP is a delayed allergic reaction caused when sensitive people inhale dusts causing their bodies to produce antibodies. Since FHP is an allergic reaction and involves the immune system, each new FHP exposure and feeling of being sick gets worse. With repeated exposure, some people become unable to work in dusty areas and can develop permanent lung damage. There are documented cases of farmers, veterinarians and others on farms who are simply hypersensitive to the point where they need to find another line of work.

FHP is caused by dust containing mold, mold spores, and bacteria that developed in warm conditions (often while these products are in storage). Heat-loving molds are more likely to grow in stored hay or top layers of silage. FHP molds can also sometimes develop in stored grain. If you’ve been diagnosed with FHP before, and get sick again while working around grain, hay or silage, you really need to visit your local clinic.

“Organic Dust Toxic Syndrome” or ODTS, the second type of illness is a toxic reaction.  It is more common.  With ODTS, your respiratory system becomes inflamed from the dust, molds, bacteria, and endotoxins in the dust. Symptoms look much like FHP. BUT, the body’s reaction causing symptoms is actually very different.  People who develop ODTS usually recover in a few days. Permanent lung damage from ODTS is rare. Again, your local health professional should be consulted if you develop this type of reaction.

Agricultural health experts face a vexing problem, as Farmer’s Lung (FHP) and Organic Dust Toxic Syndrome (ODTS) look almost identical in terms of symptoms in the first hours or days.  At times, even rural health professionals can have a hard time recognizing these illnesses and knowing the difference. Medical testing is often needed to truly tell the two apart. Medical treatment is also different. Consult the author of this article for more information that might be helpful if you visit a clinic.

Controlling Exposure:

Organic dust exposure on farms and the related health symptoms is complex. Here are specific things to reduce risk:

  • Have a clean air filter in place when operating any piece of equipment.Use correct settings on the cab blower when the heater or A/C is used to create a positive pressure inside the cab. When replacing filters, insure gaskets are installed and sealing correctly.
  • Avoid exposures to grain, hay and silage dust when possible, regardless of your sensitivity. When combining, stay in the cab with the door closed when unloading.
  • Properly adjust harvest equipment and practices (related to handling, harvest/storage moisture, etc.) to maximize quality and minimize damage and dust generated. Properly harvested products will store better with fewer mold (and insect) issues.
  • Wear a NIOSH-approved “N-95” dust mask that fits properly in conditions where dust exposure is unavoidable. CAUTION: Employees should wear a respirator only if they are free of health problems, particularly with the heart and lungs. Any long or short term illness or disease that has an impact on the heart of respiratory system can become more problematic because wearing a respirator creates additional stresses on the body. If employees need extra breating protection, a powered air purifying respirator (PAPR) or “air helmet” can be used in these situations including units that are “high efficiency” for removing contaminants. There are other complex regulatory requirements, particularly in commercial grain storage facilities. Consult experts before requiring any employee to use any type of respirator to learn about fit testing and other best practices. Also realize that respirators which help with dust filtering provide ZERO protection against toxic gases associated with manure, silo gas, or low-oxygen situations.
  • If you feel sick after exposure, call your health care provider. This is especially important if you know you are allergic to these dusts, or if your symptoms continue to get worse.
  • Smoking makes organic farm dust exposure symptoms much worse.


John Shutske, PhD, Agricultural Engineering Specialist, UW-Madison and UW-Extension (

Note that good diagnostic information for health professionals can be found at:

  • Kirkhorn SR. Agricultural Respiratory Health in Critical Need.  Partners in Agricultural Health. Wisconsin Office of Rural Health.  Available here.
  • Donham, K. J. and A. Thelin. 2006. Agricultural Medicine: Occupational and Environmental Health for the Health Professions. Ames, Iowa: Blackwell Publishing. (Chapter 3 contains information that can help a doctor in the process of differentiating between Farmer’s Lung or FHP and ODTS).
  • Girard M, Lacasse Y, Cormier Y. Hypersensitivity pneumonitis.  2009 Mar;64(3):322-34. Epub 2009 Feb 6. Review.
  • Kirkhorn SR, Garry VF. Agricultural lung diseases.  Environ Health Perspect. 2000 Aug;108 Suppl 4:705-12. Review.
  • Seifert SA, Von Essen S, Jacobitz K, Crouch R, Lintner CP. Organic dust toxic syndrome: a review.  J Toxicol Clin Toxicol. 2003;41(2):185-93. Review