Warm water changes the body in a simple way: it transfers heat into the skin and underlying tissues, which widens (dilates) blood vessels and increases blood flow. That “warming and widening” effect is one reason people often feel looser, calmer, and less tense after a bath.

In a randomized intervention study comparing warm-water immersion bathing (~40°C for 10 minutes) with showering, participants reported better fatigue, stress, pain, and mood-related measures after the bathing period than after the showering period. This was linked to the stronger “whole-body heat” effect of immersion, which can increase circulation and promote physical refreshment.

Beyond relaxation, some studies connect repeated hot-water exposure to cardiovascular changes that resemble mild exercise stress (in a controlled way). In an 8-week trial in sedentary adults, repeated hot-water immersion (“heat therapy”) used 40.5°C water for 60 minutes, 4–5 times per week and led to improvements in several vascular measures: better flow-mediated dilation (a common measure of endothelial function), lower arterial stiffness, and reductions in blood pressure, compared with a thermoneutral “sham” immersion group.

The idea is not that baths “replace exercise,” but that the heat load can trigger helpful circulation-related signals—especially for people who struggle with regular training. Sauna research also supports that heat exposure is generally well tolerated in healthy adults, while emphasizing that certain heart conditions require caution.

Foot baths are a smaller heat dose, but they may still influence the body’s “automatic” stress wiring (the autonomic nervous system). In a study of healthy young women, a 42°C footbath for 10 minutes with added mechanical stimulation (air bubbles and vibration) shifted heart-rate variability toward more parasympathetic (“rest-and-digest”) activity and less sympathetic (“fight-or-flight”) activity, alongside increases in white blood cell count and natural killer cell activity.

In patients with rheumatoid arthritis, a randomized controlled study found that warm hand-foot baths (plain warm water or warm saltwater) over six weeks improved pain, fatigue, and sleep quality versus a control group, with saltwater showing the largest pain improvement.

Bubble baths are mostly about comfort and experience, but “bubbles with vibration” in foot bathing has limited evidence for extra calming/physiological shifts. The main point is that heat + comfort + reduced sensory stress can add up to a real relaxation signal, while benefits beyond that depend on dose, safety, and the person’s health.