64 Heat Therapy Statistics

by

These heat therapy figures cover the measurement periods and populations identified in the available source material. Estimates, surveys and forecasts retain their reported scope.

Key Heat Therapy Statistics

The main findings are:

  • Approximately 489,000 heat-related deaths occurred each year worldwide during 2000–2019 studies, with 45% in Asia and 36% in Europe.
  • The U.S. study estimated 326,497 acute heat-illness ED cases from 2006–2010 (2006–2010; May–September).
  • Heat exhaustion accounted for 74.7% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs).
  • A systematic review included 32 randomized controlled trials involving 1,098 patients with delayed-onset muscle soreness (search through December 2020; multinational studies).
  • The endurance-performance meta-analysis included 10 studies and 199 participants, aged approximately 20–32 years; 156 were male and 43 female (studies through February 2024; healthy active adults and athletes).
  • A newer systematic review included 14 studies and 194 participants: 9 acute-recovery studies and 5 long-term training studies (search updated June 2025; healthy adults).
  • An estimated 61,672 heat-related excess deaths occurred in Europe in summer 2022.
  • The annualized U.S. rate was 21.5 acute heat-illness ED visits per 100,000 population per year (2006–2010; May–September).
  • Heat stroke accounted for 5.4% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs).
  • Heat treatment reduced pain within 24 hours with SMD −1.17 (95% CI −2.62 to −0.09; p=0.03) (within 24 hours after exercise; DOMS patients in RCTs).
  • Performance in hot conditions showed a trivial pooled ratio of means of 1.04 (95% CI 0.94–1.15; p=0.46) (post-exercise heat exposure trials; healthy adults in 33–40°C performance tests).
  • In the 14-study review, 4 acute studies found no performance-recovery effect, 4 found benefit and 1 found an adverse effect (studies through June 2025; healthy adults).
  • The 2003 European heatwave was associated with about 70,000 deaths during June–August (June–August 2003).
  • About 65,299 acute heat-illness ED visits occurred per summer year on average (2006–2010; May–September).
  • Nonspecific heat illness accounted for 3.7% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs).

Contents

  • Approximately 489,000 heat-related deaths occurred each year worldwide during 2000–2019 studies, with 45% in Asia and 36% in Europe. (Heat and health)
  • An estimated 61,672 heat-related excess deaths occurred in Europe in summer 2022. (Heat and health)
  • The 2003 European heatwave was associated with about 70,000 deaths during June–August (June–August 2003). (Heat and health)
  • A 44-day heatwave in the Russian Federation in 2010 was associated with 56,000 excess deaths. (Heat and health)
  • Heat-related mortality among people aged over 65 increased approximately 85% between 2000–2004 and 2017–2021 (2000–2004 vs 2017–2021; global; age 65+). (Heat and health)
  • For each 1°C increase in ambient heat above the optimal level, pooled evidence found 4% higher odds of preterm birth (pooled studies through 2024; global review of maternal/neonatal studies). (Heat and health)
  • Heatwave exposure was associated with 26% higher odds of preterm birth in a global review (pooled studies through 2024; global review of maternal/neonatal studies). (Heat and health)

WHO summary of published estimates; heat-related mortality methods vary across studies.

Excess-death estimate, not a count of clinically diagnosed heat illness.

Historical heatwave estimate; attribution is population-level.

Heatwave excess-mortality estimate, not therapeutic heat exposure.

WHO indicator compares periods and reflects environmental heat exposure.

Association from pooled observational evidence; not a therapeutic-heat trial.

Pooled observational estimate; heatwave definitions differed.

Heat illness statistics from U.S. emergency departments

Nationwide Emergency Department Sample; heat illness defined by ICD-9-CM 992.0–992.9.

Population rate based on pooled study years.

Average across five study years.

Uses total ED visits as denominator and assumes no repeat heat-illness visits.

Disposition categories from ED records; does not capture deaths after discharge or admission.

Coding-position statistic, not a severity measure.

Applies only to cases with heat illness as first-listed diagnosis.

Applies only to secondary-diagnosis cases.

Year-specific rates from pooled national ED data.

Ecological correlation; it does not establish individual causation.

Heat therapy safety statistics by age, sex, geography and diagnosis

  • Heat exhaustion accounted for 74.7% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Heat stroke accounted for 5.4% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Nonspecific heat illness accounted for 3.7% of acute heat-illness diagnoses (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Among heat-stroke cases, 62.0% were admitted or died in the ED (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Heat stroke represented 28.3% of all hospital admissions among acute heat-illness cases (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Heat stroke represented 77.0% of deaths occurring in the ED among acute heat-illness cases (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The ED case-fatality rate for heat stroke was 99.4 per 10,000 visits (95% CI 78.7–120.1) (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The highest treat-and-release rate was 26.2 per 100,000 per year among adults aged 18–45 (2006–2010; May–September; United States; age 18–45). (Summertime acute heat illness in…)
  • Adults over 65 had the highest hospital-admission rate at 6.65 per 100,000 per year (2006–2010; May–September; United States; age 65+). (Summertime acute heat illness in…)
  • Adults over 65 had the highest ED-death rate at 0.031 per 100,000 per year (2006–2010; May–September; United States; age 65+). (Summertime acute heat illness in…)
  • The male treat-and-release rate was 25.5 per 100,000 per year versus 12.1 for females (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The male hospital-admission rate was 3.7 per 100,000 per year versus 1.31 for females (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The male ED-death rate was 0.024 per 100,000 per year versus 0.006 for females (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Rural areas had a treat-and-release rate of 29.7 per 100,000 per year, compared with 13.8 in large metropolitan areas (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Rural areas had a hospital-admission rate of 3.32 per 100,000 per year, compared with 2.16 in large metropolitan areas (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The lowest-income ZIP-code quartile had a treat-and-release rate of 23.9 per 100,000 per year versus 11.9 in the highest quartile (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • The lowest-income ZIP-code quartile had a hospital-admission rate of 3.5 per 100,000 per year versus 1.49 in the highest quartile (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Uninsured patients had the highest treat-and-release rate at 28.8 per 100,000 per year (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Medicare-covered patients had a hospital-admission rate of 6.88 per 100,000 per year (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Heat-stroke cases had 23.86 times the adjusted odds of admission or ED death compared with other acute heat-illness diagnoses (95% CI 22.35–25.46) (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Male sex was associated with adjusted odds ratio 1.64 for admission or ED death in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • A chronic blood condition was associated with adjusted odds ratio 9.05 for admission or ED death in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • A chronic circulatory condition was associated with adjusted odds ratio 2.44 for admission or ED death in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Patients aged 0–17 had an adjusted odds ratio of 0.40 versus adults over 65 for admission or ED death in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Patients aged 18–45 had an adjusted odds ratio of 0.45 versus adults over 65 in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)
  • Large-metropolitan patients had adjusted odds ratio 1.36 versus rural patients in the heat-stroke model (2006–2010; May–September; United States EDs). (Summertime acute heat illness in…)

ICD-9-CM-coded ED diagnoses.

ICD-9-CM code 992.9; categories do not sum to all cases because other diagnoses were present.

Composite ED disposition outcome.

Share among heat-illness admissions, not all U.S. admissions.

Deaths in the ED only.

ED case-fatality measure; not total post-visit mortality.

Age-specific treat-and-release rate.

Age-specific rate from ED data.

Death-in-ED rate; small counts and sampling uncertainty apply.

Sex-specific rate; exposure and behavior differences are not controlled by this comparison.

Sex-specific rate.

Small event counts; death-in-ED only.

Urban-rural classification is area-level.

Area-level comparison.

ZIP-code income is an area-level socioeconomic measure.

Area-level socioeconomic comparison.

Insurance category is recorded at ED visit and may reflect access and exposure differences.

Payment-source category; not an individual causal effect.

Multivariable model; comparison is heat stroke versus other coded heat illness.

Model estimate with females as referent.

Association in a clinical model; chronic-condition coding and confounding remain possible.

Association, not proof that the condition caused the outcome.

Adults over 65 were the referent group.

Rural areas were the referent; area-level association.

Heat therapy outcomes for pain and delayed-onset muscle soreness

  • A systematic review included 32 randomized controlled trials involving 1,098 patients with delayed-onset muscle soreness (search through December 2020; multinational studies). (Heat and cold therapy reduce…)
  • Heat treatment reduced pain within 24 hours with SMD −1.17 (95% CI −2.62 to −0.09; p=0.03) (within 24 hours after exercise; DOMS patients in RCTs). (Heat and cold therapy reduce…)
  • Heat treatment reduced pain beyond 24 hours with SMD −0.82 (95% CI −1.38 to −0.26; p=0.004) (more than 24 hours after exercise; DOMS patients in RCTs). (Heat and cold therapy reduce…)
  • Hot-pack therapy reduced pain within 24 hours with SMD −2.31 (95% CI −4.33 to −0.29; p=0.03) (within 24 hours after exercise; DOMS patients in hot-pack trials). (Heat and cold therapy reduce…)
  • Hot-pack therapy reduced pain beyond 24 hours with SMD −1.78 (95% CI −2.97 to −0.59; p=0.003) (more than 24 hours after exercise; DOMS patients in hot-pack trials). (Heat and cold therapy reduce…)
  • There was no statistically significant difference between pooled heat and cold therapy groups for pain reduction (p=0.16) (post-exercise follow-up; DOMS patients in RCTs). (Heat and cold therapy reduce…)
  • Cold therapy within one hour reduced DOMS pain within 24 hours with SMD −0.57 (95% CI −0.89 to −0.25; p=0.0005) (within 24 hours after exercise; DOMS patients in RCTs). (Heat and cold therapy reduce…)

Review population and interventions varied; this is evidence volume, not an effect by itself.

Pooled RCT estimate; negative SMD indicates lower pain and confidence interval is wide.

Pooled RCT estimate; timing and heat modalities varied.

Subgroup estimate with very wide confidence interval.

Subgroup estimate; protocols and comparators varied.

A non-significant difference does not prove equivalence.

Included as a comparator context for heat therapy; not a heat outcome.

Post-exercise heat therapy statistics for endurance and physiology

  • The endurance-performance meta-analysis included 10 studies and 199 participants, aged approximately 20–32 years; 156 were male and 43 female (studies through February 2024; healthy active adults and athletes). (The effect of post-exercise heat…)
  • Performance in hot conditions showed a trivial pooled ratio of means of 1.04 (95% CI 0.94–1.15; p=0.46) (post-exercise heat exposure trials; healthy adults in 33–40°C performance tests). (The effect of post-exercise heat…)
  • Performance in thermoneutral conditions showed a pooled ratio of means of 1.06 (95% CI 0.99–1.12) across 6 studies and 144 participants (post-exercise heat exposure trials; healthy adults in 18–24°C tests). (The effect of post-exercise heat…)
  • The pooled VO2max effect was SMD 0.33 (95% CI 0.19–0.47) across 3 studies and 91 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled speed-at-lactate-threshold effect was SMD 0.19 (95% CI −0.53 to 0.92) across 3 studies and 55 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled heart-rate effect was SMD −0.32 (95% CI −0.45 to −0.20) across 6 studies and 163 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled perceived-exertion effect was SMD 0.11 (95% CI −0.38 to 0.61) across 6 studies and 163 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled core-temperature effect was SMD −0.44 (95% CI −0.79 to −0.09) across 6 studies and 163 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled sweat-rate effect was SMD 0.27 (95% CI 0.06–0.47) across 6 studies and 139 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The pooled thermal-sensation effect was SMD −0.61 (95% CI −0.98 to −0.24) across 5 studies and 112 participants (post-exercise heat exposure trials; healthy adults). (The effect of post-exercise heat…)
  • The post-exercise heat interventions lasted 5–21 days, with sessions lasting 14–40 minutes (included trials; healthy adults and athletes). (The effect of post-exercise heat…)

Small, young research samples limit generalization.

Low predictive certainty; pooled estimate was imprecise.

GRADE certainty was very low.

Very-low certainty because of risk of bias, imprecision and publication bias.

Very-low certainty and wide interval crossing zero.

Direction follows the review’s outcome coding; certainty was very low.

Very-low certainty and confidence interval crossing zero.

Review coding uses negative values for the reported direction; clinical importance is uncertain.

Very-low certainty and heterogeneous protocols.

Low certainty; thermal-sensation scales were rescaled before pooling.

Protocol range describes study designs, not a recommended dose.

Sauna and passive-heat research statistics: what trials show

  • A newer systematic review included 14 studies and 194 participants: 9 acute-recovery studies and 5 long-term training studies (search updated June 2025; healthy adults). (Effects of Post-Exercise Heat Exposure…)
  • In the 14-study review, 4 acute studies found no performance-recovery effect, 4 found benefit and 1 found an adverse effect (studies through June 2025; healthy adults). (Effects of Post-Exercise Heat Exposure…)
  • In the newer review, 6 acute-recovery studies used hot-water immersion, 1 traditional sauna and 2 infrared sauna (studies through June 2025; healthy adults). (Effects of Post-Exercise Heat Exposure…)

Review abstract reports low-to-moderate overall evidence quality.

The remaining acute studies did not fit these result categories in the abstract summary; outcomes and protocols differed.

Modality counts apply to acute-recovery studies and do not establish comparative effectiveness.

Table of contents