(1) Skin has neurons that sense changes in heat;

(2) Electrical signals are sent to the spinal cord;

(3) Signals are sent to the brain – specifically the preoptic area (POA) which send signals to the brain & body and trigger behavioral responses.

The impulse to get yourself out of a hot environment is the consequence of the POA communicating with the amygdala and in turn activating adrenal glands

• Regular use of sauna and other heat exposure can reduce mortality by cardiovascular events, stroke, and all-cause mortality.
• You will become better adapted and better at sweating excess heat with frequent exposure.
• Options if you don’t have access to a sauna: try hot water bath up to the neck – getting a similar temperature is key (176F-212F); wear a plastic suit (like fighters trying to drop weight).
• Wet sauna and dry sauna are both acceptable; most infrared saunas don’t get hot enough.

Hormone effects of heat: decrease in cortisol output.

Activation of heat shock proteins (HSP): heat changes the way in which proteins are configured at a molecular level – HSP makes sure cells of the brain and body don’t misfold

Heat for lifespan: heat upregulates pathways related to DNA repair and clearing out of senescent cells.

Heat for metabolic enhancement:  57 minutes per week (total, spread out across sessions) of heat exposure – cold exposure: 11 minutes per spread out of the uncomfortable but safe cold.

Hormesis: subjecting yourself to enough stress to induce adaptation of some kind.

• Growth hormone: impacts metabolism and growth of cells and tissues of the body, responsible for tissue repair and growth spurt during puberty.
• Starting in the early 30s, growth hormone release is greatly diminished.
• Sauna exposure increased growth hormone 16 fold – important caveat, effect on growth hormone went down with increased sauna use because body becomes heat adapted.
• If growth hormone increase is your main goal for sauna use, limit to 1x/week or 1x/10 days – and enter fasted or without food in the 2-3 hours prior for maximum benefits.

The endorphin system is activated when we experience short stress.

Dynorphin system: the struggle of heat exposure ultimately activates pathways that lead to an increase in the baseline level of mood and heightened level of happiness and improved mood.

Glabrous skin: hair-free skin found in palms of hands, soles of feet, the upper half of the face.

Glabrous skin surfaces can be leveraged to cool the blood and core of the body.

To warm a cold body: use a warm blanket or warmer on glabrous surfaces.

To cool a hot body: use a cool compress, frozen or cold materials on glabrous surfaces.

Fever is natural heat inoculation designed to kill pathogens in the body.

Cold exposure (11 minutes per week, up to the neck) has been shown to increase brown fat which increases metabolism and the ability to feel comfortable in cold temperatures.

Local heat exposure (not to the point of burning) converts white fat to beige fat which leads to systemic increases in thermogenesis, metabolism, and fat loss – children have a lot of brown and beige fat.