Prevention is not treatment

A controlled study found fewer cold episodes among healthy volunteers who used sauna regularly. It did not find shorter or less severe colds, and it did not test sauna as a treatment after a person became sick.

A long-term cohort also found that frequent sauna use was associated with fewer new respiratory disease cases. That association describes later incidence across years, not whether heat helps an infection you have today.

Do not stack heat on fever

Fever already raises body temperature, and illness can make hydration harder to maintain. Adding sauna heat increases the same burdens instead of reproducing the prevention protocols.

Symptoms below the neck are another reason to be conservative. The research does not supply a treatment protocol for active illness, so a doctor is the right person to ask about your condition.

What the research says

Ernst et al. followed 50 healthy volunteers, with 25 assigned to sauna and 25 to control, for 6 months. Their Annals of Medicine trial from 1990 found fewer cold episodes in the sauna group, concentrated in the final 3 months, while cold duration and severity did not differ. This tested prevention in healthy people, not treatment while sick.

Kunutsor, Laukkanen, and Laukkanen followed 1,935 men for a median of 25.6 years and recorded 379 new respiratory disease cases, including COPD, asthma, or pneumonia. Their European Journal of Epidemiology study from 2017 found hazard ratios of 0.73 for 2–3 sessions a week and 0.59 for 4 or more sessions compared with 1 or fewer. These were cohort associations and do not prove that sauna prevented disease or treated active illness.

Hussain and Cohen's Evidence-Based Complementary and Alternative Medicine systematic review from 2018 assessed 40 clinical studies with 3,855 participants, including 13 randomized controlled trials. It found plausible benefits but called for higher-quality evidence about adverse effects and which populations benefit.