Does sauna bathing help against infections?
There are preliminary indications that regular sauna bathing may have a beneficial effect on your immune system, but the evidence is too thin for firm conclusions. If you have joint complaints or an unusual skin condition, discuss it with your doctor before making it a regular habit.
Regular sauna bathing may reduce the severity of flu and respiratory infections. That signal comes from observational studies and narrative review articles, not from large randomised trials. These are therefore early indications, not an established clinical benefit.
A small study in 20 healthy young men showed that immune system changes only became measurable after a series of ten sauna sessions: there were shifts in white blood cells and certain types of lymphocytes. A single sauna session did not produce that effect. In addition, trained and untrained men responded differently, so it is not a given that this applies equally to everyone.
Sweat naturally contains certain protective proteins that can inhibit bacteria on the skin. Whether sauna bathing raises the concentration of those proteins compared with ordinary sweating cannot be determined from the available studies.
Animal research in mice and hamsters shows that an elevated body temperature can increase resistance to influenza virus and SARS-CoV-2, through a mechanism linked to the gut microbiome. This has so far only been demonstrated in animals; whether sauna bathing produces the same effect in humans is unknown.
There are also safety considerations. In people with joint complaints, a serious joint infection caused by a difficult-to-treat bacterium has been described following repeated steam therapy; this involved herbal steam therapy, not a classic sauna bath. People with a rare hypersensitivity to their own sweat components can develop skin rashes and severe itching from sauna bathing. For everyone else these risks appear small, but it is worth being aware of them.
All claims are based on small observational studies, one small intervention study (n=20), animal experimental research and two case reports. No large randomised trials are available.
Does green tea help against infections?
For influenza there is reasonable evidence that green tea catechins are helpful; for most other infections the data are still at the laboratory or animal stage, so use it as a complement to standard prevention, not a replacement for it.
Does sunbathing boost your immune system beyond the vitamin D effect?
Sunlight has real effects beyond vitamin D through nitric oxide and hormonal pathways, but randomised evidence for improved immune defences is lacking. At the same time, the immunosuppressive effect of chronic exposure is well documented, so moderate sun exposure makes more sense than a great deal of it.
Can too little sleep make you more susceptible to infections?
Too little sleep demonstrably makes your immune system more vulnerable, including to infections and vaccinations. Make sure you get sufficient sleep, even though the exact numbers and thresholds are not yet precisely known.
Does cold showering boost your immune system?
Cold showering produces measurable stimulation of the immune system, but whether it actually makes you less likely to fall ill has not been proven. Until better research is available, there is no harm in doing it if you enjoy it, but do not count on it as protection against infections.
Does turmeric help against inflammation?
Curcumin has a biologically plausible anti-inflammatory effect and shows reductions in inflammatory markers across multiple studies, but the results are not consistent enough for a firm recommendation. If you want to try it, choose a formulation with piperine or a liposomal variant for better absorption, and discuss it with your doctor if you are taking any medications.
Can you slow down the ageing of your immune system?
The immune system demonstrably ages, and there are promising avenues for slowing that process, but no single approach has been proven safe and effective in humans. Eating less processed food is the only step you can concretely take right now; everything else requires more research in humans before any conclusions can be drawn.