The Impact of Pets on Human Health and Psychological Well-Being: Fact, Fiction, or Hypothesis?

Abstract

Because of extensive media coverage, it is now widely believed that pets enhance their owners’ health, sense of psychological well-being, and longevity. But while some researchers have reported that positive effects accrue from interacting with animals, others have found that the health and happiness of pet owners is no better, and in some cases worse, than that of non–pet owners. I discuss some reasons why studies of the effects of pets on people have produced conflicting results, and I argue that the existence of a generalized “pet effect” on human mental and physical health is at present not a fact but an unsubstantiated hypothesis.

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Current Directions in Psychological
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DOI: 10.1177/0963721411415220
2011 20: 236Current Directions in Psychological Science
Harold Herzog
The Impact of Pets on Human Health and Psychological Well-Being : Fact, Fiction, or Hypothesis?
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Many people are deeply attached to companion animals. In the
United States, over two thirds of households include a pet,
most of which are regarded by their owners as family mem-
bers. Considering that the lifetime costs of owning a pet are
about $8,000 for a medium-sized dog and $10,000 for a cat
(cats tend to live longer than dogs), devoting resources on a
creature with whom you share no genes and who is unlikely to
ever return the favor seems to make little evolutionary sense.
Aside from the expense, there are other downsides to compan-
ion animals. In the United States, a person is 100 times more
likely to be seriously injured or killed by a dog than by a ven-
omous snake, and over 85,000 Americans are taken to emer-
gency rooms each year because of falls caused by their pets.
Further, people can contract a cornucopia of diseases from
companion animals, including brucellosis, roundworm, skin
mites, E. coli, salmonella, giardia, ringworms, and cat-scratch
fever. And, pets are second only to late-night noise as a source
of conflict between neighbors.
Although not culturally universal, pet keeping exists in
most societies, and an array of theories have been offered to
explain why people bring animals into their lives (Herzog,
2010). Among these are the misfiring of parental instincts, bio-
philia (a hypothetical biologically based love of nature), social
contagion, the tendency for the middle class to emulate the
customs of the rich, the need to dominate the natural world,
social isolation in urban societies, and the desire to teach
responsibility and kindness to children. While the reasons that
pet keeping has become a widespread cultural phenomenon
are unclear, it is evident that companion animals are vitally
important in the lives of many people.
The “Pet Effect”
When asked what they specifically get from their relationships
with pets, people typically mention companionship, having a
play partner, and the need to love and care for another crea-
ture. But fueled by media reports and books with titles like The
Healing Power of Pets: Harnessing the Amazing Ability of
Pets to Make and Keep People Happy and Healthy (Becker,
2002), the public has come to accept as fact the idea that pets
can also serve as substitutes for physicians and clinical psy-
chologists. The idea that living with an animal can improve
human health, psychological well-being, and longevity has
been called the “pet effect” (Allen, 2003).
Most pet owners believe that their companion animals are
good for them. Personal convictions, however, do not consti-
tute scientific evidence. Claims about the medical and psycho-
logical benefits of living with animals need to be subjected to
the same standards of evidence as a new drug, medical device,
Corresponding Author:
Harold Herzog, Department of Psychology, Western Carolina University,
Cullowhee, NC, 29723
E-mail: herzog@wcu.edu
The Impact of Pets on Human Health
and Psychological Well-Being: Fact, Fiction,
or Hypothesis?
Harold Herzog
Western Carolina University
Abstract
Because of extensive media coverage, it is now widely believed that pets enhance their owners’ health, sense of psychological
well-being, and longevity. But while some researchers have reported that positive effects accrue from interacting with animals,
others have found that the health and happiness of pet owners is no better, and in some cases worse, than that of non–pet
owners. I discuss some reasons why studies of the effects of pets on people have produced conflicting results, and I argue that
the existence of a generalized “pet effect” on human mental and physical health is at present not a fact but an unsubstantiated
hypothesis.
Keywords
pets, companion animals, health, psychological well-being, happiness
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Pets, Human Health, and Psychological Well-Being 237
or form of psychotherapy. Over the past 30 years, hundreds of
studies have examined the impact of pets on human health and
happiness. Here I argue that, contrary to media reports, an
examination of this body of literature indicates that the pet
effect remains an uncorroborated hypothesis rather than an
established fact. (Note that the main focus of this article is on
the effects of pets on the physical and mental health of their
owners, not the efficacy of animals as therapeutic agents for
disorders such as autism and attention-deficit/hyperactivity
disorder.)
The Evidence That Pets Are
Good for People
The first demonstration of an association between pets and
health was an early study of 92 heart-attack victims in which
28% of pet owners survived for at least a year as compared to
only 6% of non–pet owners (Friedmann, Katcher, Lynch, &
Thomas, 1980). These findings generated a flurry of research
on the positive impact of interacting with companion animals
(see review by Wells, 2009a). For example, stroking dogs and
cats, watching tropical fish in an aquarium, and even caressing
a pet boa constrictor have been reported to reduce blood pres-
sure and stress levels. The most convincing of these studies
was a clinical trial in which hypertensive stockbrokers were
randomly assigned to either pet or no-pet conditions. Six
months later, when put in a stressful situation, subjects in the
pet group showed lower increases in blood pressure than did
those in the non-pet control condition (Allen, Shykoff, & Izzo,
2001). Researchers have also reported that psychological ben-
efits accrue from living with animals. These include studies
showing that pet owners have higher self-esteem, more posi-
tive moods, more ambition, greater life satisfaction, and lower
levels of loneliness (El-Alayli, Lystad, Webb, Hollingsworth,
& Ciolli, 2006).
Epidemiologists have also connected pet ownership to bet-
ter health and well-being (see review by Headey & Grabka,
2011). For example, among 11,000 German and Australian
adults, pet owners were in better physical condition than non-
pet owners, and they made 15% fewer doctor visits, a potential
savings of billions of dollars in national health expenditures.
And an epidemiological study of Chinese women found that
pet owners exercised more, slept better, felt more physically
fit, and missed fewer days from work than women without
pets. Further, these effects were particularly strong for indi-
viduals who reported that they were very closely attached to
their pets.
Now the Bad News
Pet owners are, of course, delighted to read about research that
confirms the view that living with a dog or cat makes for a
happier and longer life. But while the media abounds with sto-
ries extolling the health benefits of pets, studies in which pet
ownership has been found to have no impact or even negative
effects on human physical or mental health rarely make head-
lines. For instance, there was no media coverage of a recent
study of 425 heart-attack victims that found pet owners were
more likely than non–pet owners to die or suffer remissions
within a year of suffering their heart attack (22% vs. 14%;
Parker et al., 2010). Indeed, replication has been a persistent
problem with research on the effects of pets on human health.
Straatman, Hanson, Endenburg, and Mol (1997), for instance,
found that performing a stressful task in the presence of a dog
had no short-term effect on blood pressure. And a study of
1,179 older adults found no differences in the blood pressure
or risk of hypertension of pet and non–pet owners (Wright,
Kritz-Silverstein, Morton, Wingard, & Barrett-Connor, 2007).
(The pet owners in the study did, however, exercise less than
non-owners and were more apt to be overweight.)
The impact of pets on psychological well-being has also
been called into question. A Pew Research Center survey of
3,000 Americans found no differences in the proportion of pet
owners and nonowners who described themselves as “very
happy” (in Herzog, 2010). Researchers in England adminis-
tered the UCLA–Loneliness scale to people who were seeking
a companion animal. When retested 6 months later, the indi-
viduals who had acquired pets were just as lonely as they were
before they got their companion animal. In addition, they were
no happier than participants who had not gotten a pet (Gilbey,
McNicholas, & Collis, 2007). Another recent study found that
older adults who were highly attached to their dogs tended to
be more depressed than individuals who were not as attached
to their companion animals (Miltiades & Shearer, 2011).
Nor has pet ownership fared well in recent epidemiological
studies. A study of 40,000 Swedes found that while pet owners
were physically healthier than non–pet owners, they suffered
more from psychological problems including anxiety, chronic
tiredness, insomnia, and depression (Müllersdorf, Granström,
Sahlqvist, & Tillgren, 2010). A Finnish study of 21,000 adults
reported that pet owners were at increased risk for hyperten-
sion, high cholesterol, gastric ulcers, migraine headaches,
depression, and panic attacks (Koivusilta & Ojanlatva, 2006).
In an Australian study of 2,551 elderly adults, dog ownership
was associated with poorer physical health and with depres-
sion (Parslow, Jorm, Christensen, & Rodgers, 2005). Finally,
in a longitudinal study of nearly 12,000 American adults, cat
or dog ownership was unrelated to mortality rates (Gillum &
Obisesan, 2010).
Reasons Why Pet-Effect Research Is
Inconclusive
For many people, pets are profoundly pleasurable and a source
of psychological support. The fact is, however, that empirical
studies of the effects of pets on human health and well-being
have produced a mishmash of conflicting results. While pets
are undoubtedly good for some people, there is presently
insufficient evidence to support the contention that, as a group,
pet owners are healthier or happier or that they live longer than
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238 Herzog
people who do not have companion animals in their lives.
Why are the results of studies on the pet effect so inconsistent?
Ioannidis (2005) argues that conflicting results and failures to
replicate are especially prevalent in areas of science in which
studies are characterized by small and homogeneous samples,
a wide diversity of research designs, and small effect sizes. He
also believes that research topics that are particularly “hot” are
especially prone to replication problems. All of these criteria
apply to research on the effects of pets on human health.
Design problems are common in studies of human–animal
interactions. Meta-analyses enable scientists to look for patterns
in the results of multiple studies on the same topic, but there have
been no meta-analyses of studies of the effects of pets on owner
happiness or health. However, for a meta-analysis in a related
area (the effectiveness of animal-assisted therapy), Nimer and
Lundahl (2007) had to comb through 250 studies to find 49 that
met even minimal standards for methodological rigor.
There is also the problem of how to interpret differences
between pet owners and nonowners. Most studies reporting
positive effects of pets are not true experiments in which the
subjects are randomly assigned to “pet” and “non-pet” groups.
Rather, they involve correlational or quasiexperimental designs
that compare people who choose to live with pets with people
who do not. Hence, while it might be the case that pets cause
their owners to be healthier and happier, it is equally possible
that the causal arrow points the other direction—that people
who are healthier, happier, and wealthier to begin with are more
likely to have the energy and financial resources required to
bring companion animals into their lives and to keep them for
extended periods. (Of course, the caution against conflating cor-
relation and causality also applies to studies in which pet owner-
ship has been found to be associated with poorer mental or
physical health.)
In addition, many studies of human–animal interactions are
based on self-reports of pet owners. While these can be useful,
self-reports sometimes produce results that are at odds with
more objective indices of health. For example, Wells (2009b)
investigated the impact of acquiring a pet on individuals suf-
fering from chronic fatigue syndrome. She found that while
the pet owners in the study claimed their animals provided
them with a host of psychological and physical benefits, their
scores on standardized measures (the Chalder Fatigue Ques-
tionnaire, the General Health Questionairre-12, and the Short-
Form-37 Health Survey) indicated that they were just as tired,
depressed, worried, and stressed as chronic fatigue sufferers
who did not get a pet.
A problem called the “file drawer effect,” which plagues
many areas of research, also skews the scientific literature on
human–animal relationships. This is the tendency for negative
results to wind up in the researcher’s filing cabinet rather than
in the pages of a scientific journal. At a session at a 2009
conference on human–animal interactions, for example, one
researcher reported that separation from their pets had no effect
on the psychological adjustment of college students, another
found that interacting with animals did not reduce depression in
psychiatric nursing home residents, and a third found no differ-
ences in the loneliness of adult pet owners and nonowners. So
far, none of these studies have appeared in print.
Finally, erroneous positive results are more common in
areas of science in which researchers have vested interests—
financial or otherwise—in a study’s outcome. Researchers are
often drawn to the study of human–animal relationships
because they are pet lovers who are personally convinced of
the healing powers of the human–animal bond. Hence investi-
gators in this field need to be particularly vigilant in designing
studies that reduce the chances of unconsciously biasing
research results. This can be especially problematic in studies
on the impact of pets on human health in which it is often dif-
ficult or impossible to eliminate placebo effects via traditional
methods such as single- and double-blind experimental and
control groups.
Why Psychologists Should Study Human–
Animal Relationships
In short, despite the growing body of research on the bonds
between people and pets, the existence of a pet effect on
human health and happiness remains a hypothesis in need of
confirmation rather than an established fact. This conclusion
should not be taken as a condemnation of pet keeping. Indeed,
companion animals have always been part of my own life, and
I understand the joys that come with living with members of
other species. Nor am I arguing that behavioral scientists
should avoid studying the impact of animals on human health
and well-being. In fact, we need more rather than less research
on this topic.
Rozin (2006) cogently observed that in their quest to
explain general principles of behavior, psychologists have
neglected huge domains of human life such as food, work, and
religion. I would add our attitudes, behaviors, and relation-
ships with other species to the list of topics that most people
find fascinating but that psychologists have for the most part
ignored. The study of our interactions with animals is interest-
ing, important, and challenging. Whether, and under what cir-
cumstances, pets make people happier and healthier is unclear.
It is, however, clear that animals play a role in nearly every
aspect of human psychological and cultural life. And our atti-
tudes and behaviors toward and relationships with other spe-
cies offer a unique window into many aspects of human nature.
Recommended Reading
Archer, J. (2011). Pet keeping: A case study in maladaptive behavior.
In C.A. Salmon & T.K. Shackelford (Eds.), The Oxford handbook
of evolutionary family psychology (pp. 281–296). New York, NY:
Oxford University Press. Provides an overview of evolutionary
theories of pet keeping.
Herzog, H. (2010). (See References). An accessible introduction to
aspects of the psychology of human–animal interactions ranging
from the effects of pets on human health and happiness to how
people make moral decisions about the use of other species.
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Pets, Human Health, and Psychological Well-Being 239
Knight, S., & Herzog, H. (Eds.). (2009). New perspectives on
human–animal interactions: Theory, policy, and research [Special
issue]. Journal of Social Issues, 65. Journal issue devoted to cur-
rent research on aspects of human–animal relationships.
McCardle, P., McCune, S., Griffin, J.A., & Maholmes, V. (Eds.).
(2011). How animals affect us: Examining the influence of human–
animal interaction on child development and human health. Wash-
ington, DC: American Psychological Association. Edited volume
focused on pets and child development but also including excellent
reviews on the impact of animals on human health and well-being.
Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to
the research, authorship, and/or publication of this article.
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