Heat, infrared and the body's response
Vasodilation
Vasodilation is the widening of blood vessels as the smooth muscle in their walls relaxes, increasing blood flow through them. Heat causes it in the skin so the body can shed heat. Blood pressure often falls as a result, which is why people can feel light-headed on standing up.
Also called vasodilatation, cutaneous vasodilation
Arteries and arterioles are wrapped in smooth muscle that is held partly contracted at rest. Relaxing it widens the vessel; because flow through a tube rises very steeply with its radius, small changes in diameter produce large changes in flow. Vasodilation is controlled by the sympathetic nervous system, by local metabolites, and by nitric oxide released from the vessel lining.
The heat response. When skin and core temperature rise, the body redirects blood to the skin so heat can be lost from the surface. Skin blood flow can increase many times over during heat stress. Two consequences follow directly:
- Cardiac load. The heart must pump more, and faster, to supply the skin without starving everything else. Heat is a genuine cardiovascular load, and that is one reason people with any heart condition should not use an ozone sauna. Check who should not use an ozone sauna before a session.
- Blood pressure. Widened vessels plus fluid lost as sweat can drop blood pressure, particularly on standing. Getting a client out of the sauna slowly, and the recommended rest afterwards, both exist for this reason.
Further reading. Increased skin blood flow during heating is everyday physiology. Our far infrared studies page collects research on heat and blood vessels and links on to its sources.
Why it matters here
It explains the flush, the faster heartbeat and the light-headedness people can feel afterwards, and it is why leaving the sauna slowly and resting for a while is part of the routine.