“Immersion in a hot tub for 10 minutes lowers blood pressure in subjects with treated hypertension, but no more than in [the non-hypertensive group].” In other words, the people with hypertension reacted the same as the people without hypertension. According to the Cleveland Clinic, a hot tub soak causes blood vessels to slightly dilate, thus lowering overall blood pressure. While it is not recommended for high blood pressure patients to constantly fluctuate between very cold water and warm water, there's nothing wrong with occasional or regular hot tub use.