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Advance Access Publication 5 December 2007 eCAM 2009;6(2)159–164
doi:10.1093/ecam/nem149
Review
Humor and Laughter May Influence Health IV. Humor and Immune
Function
Mary Payne Bennett
1
and Cecile Lengacher
2
1
Western Kentucky University, School of Nursing and
2
University of South Florida
This is the final article in a four part series reviewing the influence of humor and laughter on
physiological and psychological well-being. This final article reviews the evidence for the effect
of sense of humor, exposure to a humor stimulus and laughter on various immune system
components, with a focus on the effects of laughter on natural killer cell cytotoxicity.
Keywords: Humor – Laughter – Immune Function – Psychoneuroimmunology
Introduction
This article is the conclusion of a multipart series
reviewing the evidence currently available concerning
the influence of humor on various health outcomes. The
first article in this series discussed the basic background
of research in this area including definitions and a review
of theoretical underpinnings (1). The second article
reviewed the literature concerning use of humor as a
complementary therapy within various clinical samples,
as well as evidence concerning how a sense of humor
influences physiological and psychological well-being (2).
The third article in this series examined the influence of
the physiological response to humor (i.e. laughter) on
selected health outcomes; including muscle tension,
cardio-respiratory functioning and various physiological
measures of stress (3). This final article reviews the
evidence thus far to support the influence of sense of
humor, exposure to humor and laughter on various
immune system outcomes.
Sense of Humor and Immune Function
According to PNI theory and several recent studies, it
has been postulated that laughter or sense of humor may
affect health through moderation of stress chemicals and/
or immunoenhancement (4–7). In order to test this
theory, Martin and Dobbin (8) used a sample of 40
college students to determine if sense of humor might act
as a moderator of daily hassles on immune functioning
(8). Hassles were measured by Daily Hassles Scale
(DHS), while sense of humor was measured using the
Situational Humor Response Questionnaire (SHRQ), the
Metamessage Sensitivity Subscale (SHQ-MS), the Liking
of Humor Subscale (SHQ-LH) and the Coping Humor
Scale (CHS). Immune function was determined by
salivary IgA (SIgA). SIgA was measured at two different
times during the study, about one and a half months
apart. While scores on the SHRQ and SIgA at time two
were positively correlated (P< 0.05), all the other humor
scores and SIgA measure correlations were not signifi-
cant, and six out of eight correlations were even negative
(non-significant). These results would appear to indicate
that sense of humor has no direct effect on salivary
immune functioning, or at most, a very modest effect.
The authors concluded that sense of humor, while not
directly related to SIgA, might act as a buffer or
moderator of the effects of daily hassles on SIgA (8).
However, this supposition proposed by Martin and
Dobbin (8) was not supported by their subsequent study
that attempted to document the moderating effect of
sense of humor on the relationship between exam
stress and a variety of immune measures. Dobbin and
colleagues (9,10), examined the effect of three psycholo-
gical variables (Type A, Locus of Control and Sense
For reprints and all correspondence: Mary Payne Bennett, Western
Kentucky University, School of Nursing, AC Room 113D, 1906 College
Heights Blvd # 11036, Bowling Green, KY 42101-1036, USA.
E-mail: mary.bennett@wku.edu
ß2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/
licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original workis
properly cited.
of Humor measured by CHS) on immune functioning
following examination stress. The results indicated that,
as expected, exam stress produced significant immune
suppression as measured by decreases in T-cell
response to various mitogens, decreased IL-1beta levels
(P< 0.01) and decreased interferon gamma levels
(P< 0.05). However, the effect of exam stress was
not modified by sense of humor or any of the
measured psychological variables used. The authors
concluded that the role of psychological traits as
moderators of stress should be questioned (9,10). While
this conclusion appears too broad, considering the bulk
of literature to support the role of other psychological
factors as stress modifiers, it does call into question the
ability of sense of humor (at least as measured by CHS)
to moderate the effects of stress on physiological
functioning.
Exposure to Humor, Subsequent Laughter
and Salivary IgA
In order to determine if simply exposing people to a
humorous situation can result in immunoenhancement, a
few small studies have been conducted using humor
videos. In a randomized crossover design, 10 college
students viewed two videos, a humorous video and an
instructional video (used as a control) (11). The results of
exposure to a humorous video and sense of humor
(measured by CHS) on SIgA levels were examined. Sense
of humor scores on the CHS were positively correlated
(P< 0.05) with SIgA levels before viewing the videos,
demonstrating that subjects with greater sense of humor
also had increased salivary IgA, but scores on the CHS
were actually negatively correlated with increases in SIgA
(P< 0.10) following the humorous video. An attempt to
explain this confounding finding was suggested by the
authors, in that as the subjects with higher humor scores
had higher baseline SIgA before the film, SIgA may not
have been able to increase as much from the intervention,
due to a possible ceiling effect. But given the conflicting
data obtained when examining the relationship between
sense of humor and immune function, it may be that
sense of humor does not have a significant effect upon
this physiological outcome measure.
On the positive side, the findings did demonstrate that
subjects had significantly increased SIgA levels
(P< 0.025) after watching the humorous video (Richard
Pryor Live), indicating that exposure to humor (and
indirectly, subsequent laughter or other humor response)
can increase one measure of immune function (SIgA
levels). This supports the popular view that humor can be
healthy, but obviously needs additional support before
adoption by the scientific community.
Another publication documents results of three sepa-
rate investigations of the effect of humor on SIgA, using
college students as subjects (4). In all three studies
(n= 45, n= 34, N= 62), subjects’ salivary IgA levels
increased significantly after a brief humorous stimulus
(P< 0.005). These results clearly support the immunoen-
hancing actions of exposure to a brief humorous stimulus
on SIgA. Again, the influence of sense of humor on SIgA
levels was less clear. In an attempt to overcome possible
problems due to instrumentation, sense of humor was
measured using both SHRQ and CHS. Contrary to
Dillon’s findings, in study number one, scores on the
humor scales were unrelated to baseline SIgA, while
scores on the CHS were positively related to increases in
SIgA following the stimulus (P< 0.02). In study number
2, no significant correlation was found between sense of
humor and pre- or post-SIgA levels; and in study number
3, scores on the SHRQ were only marginally related to
increases in post-stimulus SIgA (P< 0.10).
In summary, the effect of sense of humor on SIgA and
its possible interaction with the humorous stimulus is not
clearly supported. One investigation reported that sense
of humor was negatively correlated with increases in
SIgA following the humorous stimulus (11), two others
found subjects with greater sense of humor scores had
larger increases in SIgA following the humorous stimulus
(6), and lastly one reported sense of humor was not
significantly related to SIgA levels before or following a
humorous stimulus (6). On the other hand, the effect of
exposure to humor stimulus on salivary IgA was
supported. However, it should be noted that the use of
salivary IgA as a measure of immune function has been
questioned by some authors (12,13), due to variations in
individual saliva flow rate and the use of stimulated and
non-stimulated samples in some studies. In addition, the
clinical significance of increased levels of salivary IgA is
questionable. Therefore, this body of research should be
viewed with some caution and needs replication using a
more valid and reliable measure of immune function.
Exposure to Humor, Subsequent Laughter
and Natural Killer Cell Cytotoxicity
Many PNI researchers are now using natural killer cell
cytotoxicity as an indicator of immune system function-
ing. According to Schulz et al. (14), the natural killer cell
assay is the immunoassay most likely to produce clear
and replicable results in this type of research. Natural
killer (NK) cells are lymphocytes which are classified as a
non-B, non-T or null cells. NK cells are able to lyze
tumor cell line in vitro, while leaving normal cells
intact (15). This demonstrates the ability of NK cells to
discriminate between normal and cancerous cells.
Additional in vitro data has demonstrated that NK
cells are capable of killing a wide variety of cancerous
cells including leukemia, carcinomas, sarcomas and
melanomas (15,16). Lower levels of NK cell activity
160 Humor and immune function
have been correlated with the spread of cancer, demon-
strated by increased tumor cell metastasis in both humans
and animals (17). In addition, the NK cell is a
spontaneous killer, in that it does not have to be
activated by tumor antigens, nor is it limited by major
histocompatibility complex requirements (18). There is
also some evidence that natural killer cell activity is
important in the prevention of some types of viral
illnesses, most notably those induced by herpes simplex
type 1, Epstein Barr and influenza viruses (19,20).
Cardiovascular patients in Japan demonstrated a
relationship between various psychological measures
and immune function. A positive correlation was noted
between NK cell activity and scores on both the
extraversion scale and a sense of humor scale. They
also reported a negative correlation between NK activity
and scores on the neuroticism scale. The authors stated
that the results indicate an association between general
positive feelings and higher levels of NK cell activity.
However, it should be noted that this work was
correlational and did not examine cause and effect (21).
A few researchers have attempted to document the
influence of humor and/or humor response on NK
cytotoxicity. With 22 breast cancer patients as the
sample in a randomized crossover design (22), all subjects
viewed both a humorous video and a distressing video.
NK cell cytotoxicity and numbers of NK cells were used
as outcome measures. Half of the subjects viewed the
humorous video first, while the other half viewed the
distressing video first. Blood samples were taken from an
indwelling catheter before and after each video, at 30 min
following the video, and 23 h following the first video
(just prior to viewing the second video). Sense of humor
was also included and measured using the Coping Humor
Scale (CHS). Scores on the CHS were positively
correlated with numbers of NK cells, which would
indicate that subjects with higher coping humor scores
also had more NK cells. However, contrary to what was
expected, no significant changes were noted in NK
numbers or cytotoxicity at the end of either video or
during recovery.
This unpublished dissertation also included an unex-
pected finding that NK cytotoxicity was significantly
decreased 23 h after viewing the humorous video and was
significantly increased 23 h after viewing the distressing
film. Wise suggested that this could be a rebound effect,
from a change in NK cytotoxicity (in the expected
direction) sometime in the preceding 22 h. However, it
should be noted that the 23 h post-stimulus test point was
immediately prior to viewing the second video. Perhaps
this result was related to anticipation of the upcoming
video. This is a confounding factor that needs to be
avoided in future humor research. In addition, as NK
level is known to be reduced in patients with cancer,
using cancer patients as the subjects in this investigational
work may have lead to an additional confounding factor.
Another investigation concerning the effect of humor
on NK cell activity used 10 healthy male subjects (5).
The experimental group viewed a 60 min humorous
video, while the control group watched a non-humorous
video. Blood samples were drawn from an indwelling
catheter at baseline, during the movie, and 30 min after
the movie (recovery). The experimental group displayed
significantly increased NK cell activity during and
following the humor video, from baseline to recovery
(P< 0.008), while the control group did not. However,
this study involved a very small sample and was
published in abstract form only.
In what is probably the most comprehensive report
thus far, Berk (23) reports the results of a series of five
separate studies. The results are from a total of 52
healthy males, who viewed a humor video for 1 h. Blood
samples were taken 10 min before, 30 min into, 30 min
after and 12 h after the intervention. Increases were found
in NK cell activity (P< 0.01) and immunoglobulins
G(P< 0.02), A (P< 0.01) and M (P< 0.09), with
several immunoglobulin effects lasting at least 12 h. The
authors conclude that modulation of neuroimmune
parameters by laughter may have indications for use in
health and wellness intervention programs as adjunct to
other integrative medicine therapies (23).
Most studies that document a positive effect of laughter
on NK activity have used all male samples. The use of all
male subjects in studies using immune or endocrine-based
outcomes simplifies the methodology, as it negates any
possible effects that may occur due to female hormonal
changes. However, it then becomes difficult to determine
how a particular intervention may work in women.
Because of this, a later study by our group used a sample
of 33 healthy adult women to examine the effect of
laughter on stress and NK cell activity (24). This
controlled study was designed to test the effect of
humor on NK function, and to determine if sense of
humor (measured by two different instruments) or
laughter (measured by the Humor Response Scale—
HRS) is related to change in stress NK activity when
subjects are exposed to humor. Subjects were randomly
assigned to view either a humor video or a neutral
control video, with pre and post measures of stress and
natural killer cell activity measured in all subjects.
Watching a humor video decreased stress for subjects in
the humor group, as compared to those in the distraction
group (P< 0.01). The effect of humor was apparently
mediated by humor response, as amount of mirthful
laughter correlated with the decreased stress seen in
subjects who viewed the humor video (P< 0.01). Humor
response also played a role in change in NK cell activity
following the video. Subjects who scored less than 25 on
the Humor Response Scale (indicating laughter) had
increased immune function compared with their own pre-
intervention immune function (P< 0.05), and compared
to those participants who viewed the humor video but
eCAM 2009;6(2) 161
scored below 25 on the Humor Response Scale
(P< 0.05). This finding indicated that only the subjects
who laughed out loud during the humor video had
significantly increased immune function following the
intervention. Persons who just smiled or did not have
observable responses to the humor video did not have
positive changes in immune function. This finding is
demonstrated in Fig. 1, indicating a significant relation-
ship between the amount of laughter and change in
immune function for persons in the humor group.
Similar to findings from other studies, there was no
connection between sense of humor (as measured Situ-
ational Humor Response Scale and the Multidimensional
Humor Scale) and change in any of the study outcomes.
Sense of humor was not related to change in stress,
change in NK activity or even observed laughter in
response to the humor stimulus. This finding supports
earlier work (8–10) that suggest that sense of humor
(as measured by currently available instruments) does not
appear to play a significant role in the physiological
response to a humor stimulus. Findings from this study
support that the act of laughing is correlated to changes
in stress and immune function following exposure to a
humor stimulus. Laughing can apparently reduce stress
and improve NK cell activity, at least temporarily.
As low NK cell activity is linked to decreased disease
resistance and increased morbidity in persons with cancer
and HIV disease, the authors conclude that laughter may
be a useful cognitive-behavioral intervention for use in
these patients. As an interesting side note, the differentia-
tion in the effects of smiling versus laughing out loud was
noted in another study of laughter, which examined the
effect of smiling, laughing and howling on mood changes.
It was found that howling did not substantially improve
mood but both smiling and laughing did. Moreover,
laughter seemed to boost positive affect more than just
smiling (25). Additional support for the effect of laughter
on various physiological outcomes is briefly summarized
in Table 1.
Discussion of Sense of Humor, Response
to a Humor Stimulus and NK Cell Cytotoxicity
Empirical evidence concerning the effect of sense of
humor on NK cell function is conflicting; with one study
Table 1. Brief overview of outcomes using a humorous stimulus
Health Outcome Results
Muscle relaxation Periods of intense laughter are followed by relaxed muscle tone (26,27).
Urinary epinephrine and norepinephrine
levels
Hormonal measures of sympathetic nervous system activation increased during a humorous
video (28).
Galvanic skin response and blood pressure A humorous stimulus lead to increased galvanic skin response, but stable blood pressure
indicating that while humor appears to involve activation of the sympathetic nervous
system (SNS), it also acts to buffer some of the actions of the SNS on blood pressure (29).
Changes in heart and respiratory rate Laughter leads to increased heart rate, respiratory rate and oxygen consumption (30).
Measures of anxiety, heart rate and blood
pressure
Exposure to a humorous stimulus decreased self-reported anxiety in a group of college
students who were waiting to receive an electrical shock, but did not significantly affect
physiological measures of anxiety (heart rate and blood pressure), compared to those in
the no humor control group (31).
Relaxation as measured by Biofeedback College students who scored high on internal locus of control had increased relaxation
following exposure to a humorous stimulus (32).
Various hormonal measures Berk (5). Serum cortisol, growth hormone and plasma dopac all decreased during the humorous
stimulus. No significant change was found in serum prolactin, beta endorphins, epinephrine
or norepinephrine.
SIgA Exposure to a humorous stimulus increases SIgA (6,11).
NK cell activity Wise (21) reported that exposure to a humorous stimulus did not significantly increase NK
activity. Berk (22) reported that exposure to a humorous stimulus significantly increased
NK activity (series of five studies). Finally, Bennett (24) reported that exposure to a humorous
video did not significantly increase NK activity. However, laughter in response to the humorous
video was significantly correlated with improved NK activity.
Figure 1. Plot represents the relationship between change in NK cell
functioning and subject humor response (24).
162 Humor and immune function
finding that sense of humor was related to higher baseline
levels of NK activity (23), while a second using an
intervention design did not find any relationship between
sense of humor and NK activity (24). One researcher did
report that sense of humor, as measured by psychological
self report instruments, is related to increased numbers of
NK cells in the periphery (18), but this work needs
replication in a larger sample. The overall impression
obtained from the studies conducted thus far indicates
that sense of humor has a minor role, if any, in changes
in physiological outcomes when subjects are exposed to a
humorous stimulus. However, it should be acknowledged
that this finding may be due to inadequate methods
currently available to measure sense of humor.
As for the effect of exposure to a humorous stimulus
and subsequent laughter on measures of immune func-
tion, a few small studies demonstrate an increase in SIgA
levels following exposure to a humorous video, but the
clinical benefits of increasing SIgA levels are somewhat
uncertain. Three out of four publications that report the
effect of a humorous stimulus and/or laughter on NK cell
activity indicate that exposure to a humorous stimulus or
the act of laughter can increase NK cell activity, at least
temporarily. However, it is not known if the increases
demonstrated in these studies are of a significant value to
have a clinical benefit, as long term studies looking at
health outcomes have yet to be conducted. Therefore,
additional research in this area is certainly indicated.
Humor Research Methodology and
Implications for Future Research
As can been seen from the research reviewed in this
article, humor researchers have used different conceptua-
lizations of humor and different methodologies to
examine the effect of humor, making it difficult to
summarize this body of research. In some analyses, sense
of humor is measured with a number of self-report
instruments and then correlated with various health
outcomes. The problem with this is that the various
measures of sense of humor are subject to social
desirability. Most people like to believe that they have
a good or above average sense of humor, and thus this
variable is difficult to capture using self-report instru-
ments. Experimental design is also used to determine the
effect of a humorous stimulus on health outcomes.
However, what one person feels is a humorous movie
or situation, another person may not view as being
humorous. Therefore, while these studies may determine
the outcome of viewing a supposedly humorous video in
a given set of participants, there is no guarantee that the
results obtained are, in fact, due to humor or laughter. In
order to determine the effectiveness of humor or laughter,
some objective measure of humor response is needed.
Unfortunately, most publications thus far have not
included measurement of humor response.
As previous research indicates, some subjects who
are exposed to a humorous stimulus do not laugh.
In addition, what one person views as a humorous
stimulus, another person may not find funny. This has
been addressed in earlier work by allowing subjects a
choice of different videos, etc., but it is still possible for a
person to choose a video and still not find it funny, or at
least not funny enough to produce laughter. Humor
response is known to be affected by environmental
conditions, and it can be difficult for subjects to relax
and laugh at a humor video when experimental conditions
require blood draws for laboratory testing. To help control
for this, it is critical that future humor research includes
some measure of subject response to the humorous
stimulus. Videotaping subject responses and then measur-
ing these responses with observer rating scales such the
Humor Response Scale can help document the effect of
individual humor responses to the stimulus.
Another concern is that of control groups. While
experiments using a humorous stimulus should include
some type of neutral stimulus to control for factors such as
the passage of time, experimental conditions and the
relaxation that might be associated with watching an
interesting video of some type, many of the earlier studies
did not include this type of control. It is also difficult to
select a truly ‘neutral stimulus’, in that what one person
may feel is a neutral stimulus, someone else may find
amusing, etc. And to more completely control for other
possible mechanisms which might affect health outcomes,
Martin (33) has suggested the need for at least two
additional control groups. A negative control group, which
would watch a video intended to produce emotions such as
fear or sadness, to control for the possible effects of
‘general emotional arousal’ and a positive control group
who would view a video intended to produce positive
emotions such as joy or happiness, but not necessarily
laughter, to control for the effect of positive emotions.
Of course, all of these additional control groups add to
the complexity of the design and analysis, and would
require some measure of the emotions supposedly evoked
by videos, to be sure that a subject who viewed the
negative video actually experienced negative emotional
arousal, etc. As can be seen, research design in this area
can be quite challenging. Clearly, more groundwork is
required to determine the best methods of testing and
documenting psychological and physiological outcomes
of humor in various populations. The next step is to
incorporate the prior methodological work into future
humor research design and investigate the phenomena in
larger samples of healthy subjects. In addition, small
clinical pilot studies may be used to investigate the
possibly different effects of humor in different clinical
populations.
eCAM 2009;6(2) 163
Conclusions
Research results concerning humor and healing are thus
far rather tentative, and more work is needed before
broad claims can be made concerning an effect of humor
upon health outcomes. While in a frequently cited case
study, Cousins (34) attributed his cure from ankylosing
spondylitis to complementary therapies including laugh-
ter, empirical research supporting this type of response is
currently not available. In fact, as can be seen from the
above review, documentation of the effects of humor on
various health related outcomes in healthy populations is
still in the infancy stages, and research documenting
benefits in a clinical population (such as persons with
cancer) is yet to be established.
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Received July 25, 2007; accepted July 26, 2007
164 Humor and immune function
