Soaking in a hot tub can bring many health benefits. In fact, the word "spa" is an acronym for the Latin “salus per aquam”, which literally means "health from water." Ancient cultures - including the Egyptians, Greeks, and Romans - used spas for therapy and relaxation.
Everyone knows that a hot tub is hot. But not everyone knows of the great benefits to the body when you spend a few minutes in your spa. When your body absorbs heat, several subtle physiological processes occur. First, as your body warms up, blood flow is increased. The warming of your blood causes your blood vessels to dilate. Blood pressure is subsequently reduced - often in as little as 20 minutes.
Additionally, the hot water also causes muscle relaxation as heat from the water is carried deep into your muscles. Normally, your body tries to cool itself by carrying heat to the surface via your blood. Unlike a bathtub, a spa can maintain a hot water temperature indefinitely. So while you are soaking in a spa, your blood doesn't recirculate at a reduced temperature. It returns deep within your body at a warmer temperature than before, delivering therapeutic heat where other treatments cannot.
Furthermore, the central nervous system's sensitivity it muted, as your body focuses its attention on the heat gain. This brings about temporary pain relief. This neurological affect can happen with any gradual increase or decrease in your body's temperature - but soaking in warm water is certainly nicer than the alternative!