For most illnesses, there is a clear boundary that determines whether a sauna is safe: the fever line. Do you have a fever? If the answer is yes, you must strongly avoid the sauna. When your core body temperature is already elevated by a fever, exposing yourself to 65°C-90°C heat can dangerously overload your cardiovascular system and cause severe dehydration. Even with the flu or stomach problems (vomiting/diarrhea), the risk of fluid loss is simply too high. Only if you have mild, early cold symptoms without a fever and are using a private sauna can you even consider a short session.Click here to learn more