Tradition dictates that the sweat lodge experience last for several hours. Proponents of sweat lodges believe that the ceremonial aspects of sweat lodges make the heat easier to tolerate than if you were to sit in a standard sauna.
Everyone is different. While some people can tolerate the sweat lodge experience for hours the first time they participate, others find that 45 minutes is the limit. Some people participate in sweats for years only to develop intolerance for the heat as they age. Those participating in a sweat to treat a medical condition should be particularly cautious. Sweats are considered an effective treatment for head colds, sinus problems, arthritis, asthma and some skin conditions, but it's important to listen to your body.
There are very real health risks that can come with participating in sweats. The intense exposure to heat can result in dehydration or heat exhaustion. If you don't recognize the warning signs of these conditions, you might not step out of the sweat lodge in time. Don't try to tough it out if you experience a headache, muscle weakness, nausea, a dry or sticky mouth, or fatigue. These can be signs of either dehydration or heat exhaustion.
The heat is not the only safety concern in a sweat lodge. If the people running the sweat lodge are inexperienced, they may choose rocks that are wet or contain air pockets. When these rocks are heated, they can develop cracks and, reportedly, even explode. If a hot rock explodes inside the sweat lodge, extremely hot fragments of sharp rock shoot through the air. This can be prevented by using dry river rocks and not reusing rocks for more than one sweat.
A final concern is the cedar, sweet grass and tobacco that may be thrown onto the stones. If these offerings were treated with pesticides when they were grown, that pesticide residue can become airborne and will be inhaled by people participating in the sweat. It makes sense to ask if the offerings were grown organically and, if not, whether you can participate in a sweat where they aren't used.