Saunas are helpful when it comes to the digestive system due to helping increase circulation throughout the body. Improving your circulation while constipated can help get your body back on track and push out impacted stools.
While there are several conditions listed where you should either avoid the sauna or seek medical advice, constipation is not one that is usually listed. Some might have the concern that during your session your body and muscles may relax enough that you may need to poop, but this is not a common concern.
When you detoxify, poop is one of the common ways for those toxins to exit your body. Your body is getting rid of toxins from your body, many of these we get from the food our bodies cannot process correctly so these need to be released through poop.
Traditional saunas promote detoxification by warming up the room to about 150-200°F and causing those inside to sweat out toxins. They rely on heating with rocks or wood-burning stoves, with modern ones using an electric coil.
The infrared sauna helps with detoxification by heating the body using infrared lights and heaters. The skin soaks up the heat, raising the body temperature from within, which is far more efficient than traditional saunas.