Does laughter improve immune function?
Weak EvidenceNO
Weak evidence suggests laughter may transiently increase certain immune markers (NK cell activity, salivary IgA) and reduce cortisol, but studies are small, methodologically limited, and no research demonstrates that laughter prevents infections or improves clinical immune outcomes.
The Verdict
Weak evidence suggests laughter may transiently increase certain immune markers (NK cell activity, salivary IgA) and reduce cortisol, but studies are small, methodologically limited, and no research demonstrates that laughter prevents infections or improves clinical immune outcomes.
What the Evidence Shows
The idea that laughter boosts immunity has been popularized since Norman Cousins' 1979 book 'Anatomy of an Illness' and subsequent psychoneuroimmunology research. Several small studies have measured immune biomarkers before and after laughter-inducing stimuli (comedy videos, laughter yoga, humor therapy). The most commonly cited findings include: Lee Berk's studies showing increased NK cell activity and reduced cortisol following 60 minutes of comedy viewing; studies showing elevated salivary IgA (a mucosal immune marker) after laughter; and reduced inflammatory markers following humor interventions. However, critical methodological problems pervade this literature. Sample sizes are extremely small (typically 10-30 participants). Most studies lack proper control groups—watching any engaging content (drama, documentary) may produce similar effects through relaxation and distraction. The biomarkers measured (NK cell activity, salivary IgA) are surrogate endpoints that do not reliably predict resistance to infection or disease outcomes. Changes are transient, returning to baseline within 12-24 hours. Publication bias is likely extreme in this feel-good research area. No study has demonstrated that regular laughter reduces infection rates, improves vaccine responses, or enhances recovery from illness. The positive associations may be confounded by the social connection that typically accompanies laughter, which independently affects immune function. While laughter is unlikely to be harmful and may improve subjective wellbeing, claims about meaningful immune enhancement remain unsupported by rigorous evidence.
Evidence Quality
1
Meta-Analyses
4
RCTs
8
Observational
Important Caveats
- ⚠️ Studies use small samples (10-30 participants) with poor or absent control groups
- ⚠️ Immune biomarker changes are transient (12-24 hours) and may not reflect clinical immune competence
- ⚠️ No studies demonstrate reduced infection rates or improved clinical immune outcomes from laughter
- ⚠️ Any engaging or relaxing activity may produce similar transient biomarker changes
- ⚠️ Social connection during group laughter may drive observed effects rather than laughter itself
Population Studied
Healthy adults aged 20-65 in laboratory settings; some studies in elderly nursing home residents and cancer patients; predominantly small convenience samples
Dosage
Studies typically used 30-60 minutes of laughter-inducing stimuli (comedy films, laughter yoga sessions); no established 'dose' for immune effects
Duration
Single-session measurements with biomarkers assessed 0-24 hours post-laughter; very limited chronic intervention data (laughter yoga programs of 4-8 weeks)
Supporting Studies (2)
Modulation of neuroimmune parameters during the eustress of humor-associated mirthful laughter
RCTBerk LS, Felten DL, Tan SA, Bittman BB, Westengard J. · Alternative Therapies in Health and Medicine (2001)
In 52 healthy men, viewing a 60-minute comedy video increased NK cell activity by 27%, reduced cortisol by 39%, and increased activated T-cell counts compared to a neutral documentary control group, with effects measurable up to 12 hours post-intervention.
View paper (DOI) →The effect of mirthful laughter on stress and natural killer cell activity
RCTBennett MP, Zeller JM, Rosenberg L, McCann J. · Alternative Therapies in Health and Medicine (2003)
Participants randomized to watch a humor video showed significantly increased NK cell cytotoxicity and salivary IgA levels compared to those watching a neutral tourism video, with effects correlating with self-rated humor enjoyment intensity.
View paper (DOI) →Contradicting Studies (1)
A systematic review of the evidence for the effectiveness of laughter interventions on subjective and objective health outcomes
Meta-Analysisvan der Wal CN, Kok RN. · Complementary Therapies in Medicine (2019)
Systematic review of 29 studies found very low quality evidence for immune effects of laughter, with high risk of bias in all included studies, no blinding, inadequate controls, and no demonstration of clinically meaningful immune improvements or reduced infection susceptibility.
Why this disagrees:
Highlights that the entire laughter-immunity literature is characterized by poor methodology: tiny samples, lack of blinding, absence of active control groups, use of surrogate biomarkers rather than clinical endpoints, and publication bias favoring positive results in this popular research area.
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