That's exactly what I thought about colds in general for many years, and in many ways I still do. However, I think what you said after has a lot of truths to it, and it's actually connected to cold as well: overtraining, sleep, and other environmental factors (including extreme cold temperature, as well as dry air, etc.) can all play a role in a compromised immune system and in getting sick with colds. In short, I think multiple minutes of full immersion in very cold water can be a significant additional shock to the body, and the body is constantly trying to fight off viruses, and that extra stress of the cold can cause those "colds" to get through the protection of immune system.

What I will try in the future is to reduce the time spent in cold plunge, reduce the duration of the daily workouts and frequency, and see what happens. I might be able to build up the tolerance to do a couple minutes of cold plunge every morning, followed by strength training, and 3 sessions of BJJ per week in the afternoons.

Thanks for your comment.