Short read
Edzard Ernst and colleagues at the University of Vienna ran a controlled prospective study with 50 volunteers in Austria, published in Annals of Medicine in 1990. Over six months, 25 people used the sauna regularly and 25 used neither sauna nor comparable procedures. The frequency, duration and severity of common colds were recorded in both groups. Ernst later became known as a critic of unsupported complementary medicine.
Compared with the group that avoided the sauna entirely, the sauna group had significantly fewer cold episodes. The difference was most pronounced in the last three months, when the frequency was roughly halved. Duration and severity of colds did not differ between the groups. This is one of the few studies in which the comparison group used no sauna at all.
The study is small, with 50 people, and dates from 1990. There was no blinding, and participants recorded their symptoms themselves. The authors concluded that further studies were needed to confirm the hypothesis.
Two details matter more than the headline figure. Sauna use was not associated with shorter or milder colds, only with fewer of them. And the difference only became visible after about three months, so the data give no basis for using the sauna as an acute measure. With 50 participants, the result is a lead for further research rather than a settled finding.