December 7, 1998
The Association of Health Effects
with Exposure to Odors from Hog
North Carolina Department of Health and Human Services
A. Dennis McBride, MD, MPH
The purpose of this paper is to address the public health risks posed
by exposure to odors from hog farm operations.
The number of hogs in North Carolina has increased from around two
million in 1989 to greater than 11 million in 1998. These hogs are grown
in industrial style facilities that have confinement buildings with each
holding several hundred hogs. These facilities include multi-acre lagoons
for storage and anaerobic digestion of manure and spray fields for
application of the liquid from the lagoons. The confinement buildings,
lagoons, and spray irrigation are sources of odors.
As the number of hogs produced has increased greatly and as the human
population has increased steadily in North Carolina, more people are
living near hog farms. Health and environmental agencies have received
numerous complaints from individuals living near hog operations. Their
primary complaints are annoyance with the odors and concerns about health
risks from exposure to the odors. Many North Carolina citizens are upset
that they are exposed to odors and do not have any control over their
environment. In many cases, citizens have received very little
communication from hog farm owners and from state government agencies
about the odors. The authors of "Control of Odor Emissions from Animal
". . . the attitudes and beliefs of some residents in
southeastern North Carolina counties were probed through five focus
groups held during June of 1998. Results showed that while some odor
emission from animal operations is recognized as an inevitable part of
rural life, the current situation is unacceptable, has caused
controversies that divided communities and should be addressed. All
groups agreed that state government should enforce current regulations
and that there is a need to implement more technology to better control
A review of the current scientific literature on the association of
health effects and exposure to odors from hog operations is presented.
There are several articles available addressing odors in general and a few
articles addressing health effects reported by people living near hog
farms. The paper will cover briefly the vast amount of data on the health
risks to people working in and around hog confinement buildings.
Health Effects from Exposure to Odors - General
Exposure to environmental odors results in physiological stresses that
may result in a variety of symptoms including headache, nausea, loss of
appetite, and emotional disturbance. Odors may exacerbate stress-related
illnesses. The symptoms may result from odor annoyance, stress associated
with odor exposure, and conditioned responses to odors. The literature
also reports that exposure to odors may exacerbate asthma symptoms. The
following are excerpts from articles that address human response to
N. P. Shukla (1991) "In the case of humans, the immediate
physiological stresses produced by odours can cause loss of appetite and
food rejection, low water consumption, poor respiration, nausea, and
even vomiting, and mental perturbations. In extreme cases, offensive
odours can lead to deterioration of personal and community well-being,
interfere with human relations, deter population growth and lower its
Dennis Shusterman (1992) "Environmental odor pollution
problems generate a significant fraction of the publicly-initiated
complaints received by air pollution control districts. Such complaints
can trigger a variety of enforcement activities under existing state and
local statutes. However, because of the transient timing of exposures,
odor sources often elude successful abatement. Furthermore, because of
the predominantly subjective nature of associated health complaints, air
pollution control authorities may predicate their enforcement activities
upon a judgement of the public health impact of the odor source. Noxious
environmental odors may trigger symptoms by a variety of physiologic
mechanisms, including exacerbation of underlying medical conditions,
innate odor aversions, aversive conditioning phenomena, stress-induced
illness, and possible pheromonal reactions. Whereas relatively
consistent patterns of subjective symptoms have been reported among
individuals who live near environmental odor sources, documentation of
objective correlates to such symptoms would require as yet unproven
research tools. Therefore, given our current state of knowledge, any
differential regulatory response to environmental odor pollution, which
is based upon the distinction between community 'annoyance reactions'
and 'health effects', is a matter of legal not scientific
Shim and Williams (1991) "Many patients complain that some
odors worsen their asthma. Perfume and cologne are two of the most
frequently mentioned offenders. Four patients with a history of
worsening asthma on exposure to cologne underwent challenge with
cologne, and their pulmonary function was tested before, during, and
after the exposure. Forced expiratory volume in one-second declined 18
to 58 percent below the baseline period during the 10-minute exposure
and gradually increased in the next 20 minutes. Saline placebo
pretreatment did not affect the response to subsequent challenge. Single
pretreatment with metaproteronol and atropine prevented decline in
one-second forced expiratory volume in three of four patients and
blunted the response in the other. Cromolyn sodium prevented decline in
one of four, and occlusion of nostrils prevented decline in one of
three. A survey of 60 asthmatic patients revealed a history of
respiratory symptoms in 57 on exposure to one or more common odors.
Odors are an important cause of worsening of asthma. From a practical
standpoint, sensitive asthmatic patients should be advised to eliminate
odors from their environment as much as possible."
Susan Knasko (1993) "The effects of intermittent bursts of
pleasant, unpleasant, and no experimental odor on human task
performance, mood, and perceived health weretested in this study. Odors
did not influence any of these measures; however, subjects who had been
exposed to the malodors reported retrospectively that they thought the
odors had a negative effect on all of these factors."
Pierre Caralini (1994) "With regard to general health
complaints, it was found that when exposed to odorant concentrations,
some people are annoyed and of these people, only some report general
health complaints. Exposure in itself does not directly cause general
health complaints. Annoyance is the intervening variable between
exposure and general health complaints. A possible explanation for the
relation between annoyance by malodor and general health complaints
might be found in the personality and attitudes of the exposed
individual. Finally, we found confirmation for the appraisal hypothesis,
i.e., the extent to which individuals regard malodor as threatening is
positively related to odor annoyance."
Shusterman, et. al. (1991) "Retrospective symptom prevalence
data, collected from over 2000 adult respondents living near three
different hazardous waste sites, were analyzed with respect to both
self-reported 'environmental worry' and frequency of perceiving
environmental (particularly petrochemical) odors. Significant positive
relationships were observed between the prevalence of several symptoms
(headache, nausea, eye, and throat irritation) and both frequency of
odor perception and degree of worry. Headaches for example, showed a
prevalence odds ratio of 5.0 comparing respondents who reported noticing
no such odors and 10.8 comparing those who described themselves as 'very
worried' versus 'not worried' about environmental conditions in their
. . . Potential explanations for these observations
are presented, including the possibility that odors serve as a sensory
cue for the manifestation of stress-related illness (or heightened
awareness of the underlying symptoms) among individuals concerned about
the quality of their neighborhood environment."
Sources of Air Contaminants and Odors in Hog Confinement
A University of Iowa researcher, Kelly Donham, and his co-workers have
extensively studied air pollutants and odor sources, their components, and
health impacts on people working in hog confinement buildings. Numerous
sources of air contaminants in indoor confinement facilities have been
identified. The hogs themselves shed various proteins from their saliva,
skin, urine and feces. Feed particles, pollens, molds, bacteria, fungi,
endotoxins, other various microbial proteins and grain mites and other
insect body parts can be detected in confinement houses. (Donham, 1993).
Many of these particles are of respirable size (<10um) and may be
inhaled into the small airways and alveoli of the lungs (Hill, Kenworthy,
1970). Dust particles may absorb toxic irritating gases such as ammonia,
as well as bacteria, endotoxins and other proteins and transport these to
the alveoli and small bronchioles. A literature review by O'Neill and
Phillips (1992) on odorous chemicals in livestock waste and the air around
them identified 168 different compounds. The most commonly reported
compounds in the literature review were volatile fatty acids (acetic,
propionic, butanoic and pentanoic), phenol, p-cresol and ammonia. Clayton
and Clayton, (1993) have identified some of these compounds as respiratory
tract, skin or eye irritants. These biological and chemical compounds and
dust particles comprise the potential agents of exposure to humans working
in hog operations and possibly living adjacently to hog operations.
Health Effects of Exposure to Air Contaminants and Odors Generated by
Hog Confinement Facilities
Many studies have reported the health effects experienced by people
working in hog confinement buildings. Donham et. al. (1989) reported the
following acute symptoms and prevalence rates in a study of hog
- cough (67%)
- phlegm production (56%)
- scratchy throat (54%)
- runny nose (45%)
- burning and watery eyes (39%)
- headaches (37%)
- chest tightness (36%)
- shortness of breath (30%)
- wheezing (27%)
- muscle aches and pain (25%)
Schwartz et. al. (1990) reported that chronic effects are manifested as
bronchitis, where airway obstruction was present affecting up to 25% of
hog house workers. Long term lung damage may occur as pulmonary function
tests indicate air trapping in lungs and a persistent leukocytosis.
A carefully designed five year prospective study conducted by Donham
et. al. (1990) compared respiratory symptoms in hog confinement workers
with sex-race-age-matched comparison groups of non-confinement hog farmers
and blue collar (postal) workers. As a consequence of this design, the
association between prevalence of chronic respiratory symptoms and the
degree of exposure to airborne substances associated with hog production
(confinement operations vs. non-confinement operation vs. blue collar)
could be examined. The results showed an exposure-related response with
chronic cough reported by nearly 20% of the confinement workers, 14% of
the non-confinement workers, and 8% of the blue collar workers. Chronic
phlegm production was reported by nearly 25% of the confinement workers,
11% of the non-confinement workers, and 6% of the blue collar workers.
There is a statistically significant increase in the prevalence of two
chronic symptoms in the confinement workers over that of the postal
workers (p<0.001). In addition, for work-related symptoms, there was
also a very high prevalence of acute respiratory symptoms in hog operation
workers working outside of hog houses.
The fact that some of the non-confinement workers experienced the same
symptoms as some of the confinement workers indicates that exposure to
substances associated with hog production may cause symptoms in open-air
situations. This raises the question as to whether gases and/or particles
from swine operations occur in sufficient concentrations to induce similar
respiratory symptoms in neighboring residents. The fact that plumes of
odor from large hog operations travel for several miles indicates that
neighbors are being exposed to some unknown extent to odor causing
substances from hog facilities.
Human Studies - Neighboring Residents
Little data are available about residential exposure to air
contaminants generated by hog confinement facilities. While there are
qualitative data describing the nature of the contaminants, work to
determine quantitative levels of exposure to these agents is only in a
rudimentary stage and will require many resources and much time as
environmental conditions differ from site to site and within a site over
time. Temperature, precipitation, wind direction and speed, and varying
terrain are just a few environmental conditions contributing to the
difficulties of assessment of exposure to environmental odors.
A recent study in Iowa by Thu et. al. (1997) collected mental and
physical health information by personal interviews from a random sample of
18 residents living within two miles of a 4,000 sow operation. These data
were compared to those collected from a demographically comparable sample
of 18 rural residents living in an area with minimal livestock production.
The results of the comparison indicated that "neighbors of the large-scale
swine operation reported experiencing significantly higher rates than the
controls of four clusters of symptoms that are known to represent toxic or
inflammatory effects on the respiratory tract. These clusters of symptoms
have been well documented among swine confinement workers."(Thu et al,
1997) The specific symptoms reported are listed below and are quite
similar to the list of symptoms reported by hog farm workers: (Thu et.
- increased sputum production
- shortness of breath
- chest tightness
- runny nose
- scratchy throat
- burning eyes
- muscle aches and pains
- skin rash
However, among the control group, symptoms of skin rash, muscle aches,
and fever were more frequently reported. Additionally, there was no
difference in the frequency of reported symptoms and distance from the
swine facility as one might suspect. This study found that neighbors did
not suffer higher rates of psychological health problems such as
depression or anxiety when compared to controls. Thu et. al. also state
that all responders felt the owner of the farm was creating social and
class divisions within that community.
Another study was conducted in Michigan (Warner et. al., 1990). It was
designed to assess the impact of a 50,000 animal population swine-growing
facility as an odor source and potential health problem. In parallel with
the measurement of odor intensity, the Michigan Department of Public
Health conducted a health survey to obtain information regarding the
pervasiveness of the odor in the community and its possible health
implications. Citizens' complaints reported included physical symptoms
such as breathing difficulties, burning sensations in the nose and throat,
nausea and vomiting, and headaches. A survey of residents within 0.5 miles
of the center of the facility (58 households/89 persons) and those between
0.5 and 1.25 miles away (176 households/225 persons) resulted in response
rates of 55% and 49%, respectively. The authors concluded the following:
"These responses contained complaints of symptoms attributable to the
swine facility. As with any population, symptoms as general as those which
relate to complaints as noted are difficult to correlate to specific
health problems. However, the clear excess of complaints stands as a fact
of record. Perhaps further study is needed to surface a better
understanding of individual health effects and symptoms as these relate to
perception of odor." (Warner et al, 1990). However no information is
provided on the type of complaints nor was there any report on frequency
of symptoms or whether they differed by proximity to the farm.
Schiffman et. al., (1995) evaluated 44 individuals living near hog
operations (experimental group) and 44 control subjects. These two groups
were matched on the basis of age, gender, race, and educational level.
Compared to controls, the experimental group had statistically significant
increases in tension, depression, anger, fatigue, and confusion scores
from the standardized Profile of Moods State questionnaire (McNair et al.,
1992). Schiffman states that the mood alteration could be caused by "a)
the unpleasantness of the sensory quality of the odor; b) the intermittent
nature of the stimulus; c) learned (via conditioning) aversions to the
odor, and are well documented in the scientific literature; d) potential
neural stimulation of immune responses via direct neural connections
between odor centers in the brain and lymphoid tissue; e) direct physical
effects from molecules in the plume including nasal and respiratory
irritation; f) possible chemosensory disorders; and g) unpleasant thoughts
associated with the odor."
Summary and Conclusions
The significant increases in the number of hogs and the steady increase
in the number of people in North Carolina have resulted in more contact
between people and hog odors. People are reporting to health and
environmental agencies that odors from hog farms are a nuisance and that
they are concerned about the health risks posed by exposure to the odors.
The Odor Control Task Force of the North Carolina Agricultural Research
Service at North Carolina State University reported, in regards to odors
from hog farms, that "the current situation is unacceptable, has caused
controversies that have divided communities, and should be addressed." The
sources of odors are confinement buildings, lagoons, and spray
The State Health Director is aware of three studies in the scientific
literature reporting on health studies of people living near hog farms.
These studies indicate that people living near hog farms report more
adverse health effects (including respiratory and irritation symptoms and
emotional disturbance) than people living away from hog farms. In
addition, the literature on exposure to odors in general documents that
exposure to odors in specific situations results in adverse health
effects. In addition, hog farm workers are known to experience a high
prevalence of adverse health effects including acute and chronic
respiratory symptoms. The air in hog confinement buildings has been found
to contain many gaseous and particulate chemicals some of which are known
to be respiratory irritants. These findings support the premise that
exposure to hog farm odors may result in adverse health effects. It should
be noted that the odor exposure/health effects association exists for
people with frequent exposure to the odors and does not apply to people
with one-time or infrequent exposure to odors. At present, it is difficult
to quantify or establish a dose-response relationship for environmental
exposures to hog farm odors. The State Health Director recognizes the need
for more epidemiologic studies of the association of health effects with
exposure to hog farm odors. Nevertheless, as a preventive public health
policy, the State Health Director considers exposure to hog farm odors as
a public health risk and recommends that efforts be made to minimize odor
exposures. The State Health Director encourages farm owners/operators and
regulators to take actions to minimize odor and inhalation exposures for
hog farm workers and hog farm neighbors.
Clayton and Clayton, Patty's Industrial Hygiene and Toxicology,
Fourth Edition. John Wiley and Sons, New York, 1993.
Donham, KJ. Respiratory Disease Hazards to Workers in Livestock and
Poultry Confinement Structures. Sem. Resp. Med.; 14(1) p. 49,
Donham, KJ and Leininger, JR Animal Studies of Potential Chronic Lung
Disease in Swine Confinement Buildings. Am J. Vet. Med.; 45: p.
Donham KJ, Merchant JA, and Lassise D. Preventing Respiratory Disease
in Swine Confinement Workers: Intervention Through Applied Epidemiology,
Education and Consultation. Am. J. Ind. Med.; 18: p. 241, 1990.
Hill I. R., and Kenworthy R., Microbiology of Pigs and Their
Environment in Relation to Weaning. J. Appl. Bact.; 33, p. 299,
McNair, DB, Lorr M., and Droppleman LF, Manual: Profile of Mood
States. Revised 1992, Educational and Industrial Testing Service, San
Odor Control Task Force North Carolina Agricultural Research Service,
College of Agriculture and Life Sciences, North Carolina State University,
Control of Odors from Animal Operations, A Report from the Board of
Governors of the University of North Carolina. September 1, 1998.
O'Neill, DH and Phillips, VR A Review of the Control of Odor Nuisance
from Livestock Buildings; J. Agric. Eng. Res.; 53; p. 23, 1992.
Pierre M. Caralini, Industrial Odorants: The Relationship Between
Modeled Exposure Concentrations and Annoyance, Archives of
Environmental Health, September/October 1994, Vol. 49, No. 5, pp.
Schiffman SS, Miller EAS, Suggs MS, and Graham BG. The Effect of
Environmental Odors Emanating from Commercial Swine Operation on the Mood
of Nearby Residents. Brain Research Bulletin 37(4): 369-375.
Schwartz DA, Donham KJ, and Popendorf WJ Are Workshift Changes in Lung
Function Predictive of Underlying Lung Disease? 1990 World Conference on
Lung Health, American Lung Association, American Thoracic Society,
Shim C., M.D. and Williams M.H., Jr., M.D. Effect of Odors in Asthma.
The American Journal of Medicine, Vol. 80, January 1986 pp.
Shukla NP, Air Pollution by Odor-Sources. Identification and Control,
Reviews on Environmental Health, Vol. 9, No. 4, 1991, pp.
Shusterman D., Lipscomb J., Neutra R. and Satin K., Symptom Prevalence
and Odor Worry Interaction near Hazardous Waste Sites. Environmental
Health Perspectives; Vol. 94, 1991, pp. 25-30.
Shusterman D., Critical Review: The Health Significance of Odor
Pollution, Archives of Environmental Health, January/February 1992,
Vol. 47, No. 1, pp. 76-87.
Susan Knasko, Performance, Mood, and Health During Exposure to
Intermittent Odors, Archives of Environmental Health,
September/October 1993, Vol. 48, No. 5, pp. 305-308.
Thu K., Donham KJ, Ziegenhorn R., Reynolds S., Thorne PS, Subramanian,
Whitten P., Stookesberry J. A Control Study of the Physical and Mental
Health of Residents Living near a Large-Scale Swine Operation. J.
Agric. Safety and Health; 3(1): 13-26 1996.
Warner PO, Sidhu KS, and Chadzynski L. Measurement and Impact of
Agricultural Odors from a Large-Scale Swine Production Farm, Vet Hum
Toxicol 32(4) pp. 319-323. 1990.
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