AMA #7: Cold Exposure, Maximizing REM Sleep & My Next Scientific Studies

KEYPOINTS

• 01

  Brief deliberate cold exposure is unlikely to give you a cold by itself

  Huberman's answer to the main question is 'probably not directly,' provided sessions stay in the typical range of about 1–6 minutes (10 minutes for people who really push it) and you warm up afterwards with clothes, a sauna or a hot shower. He sees no mechanism by which the cold water itself, assuming it is clean, would raise susceptibility to an upper respiratory infection.

• 02

  Cold, dry air around the session is the more plausible risk

  Laboratory studies that tightly control room humidity and temperature indicate that cold, dry air increases susceptibility to viral and bacterial infection. The nose, mouth and back of the throat are the main entry points, and their mucus lining traps pathogens. Cold, dry air thins and weakens that lining, while warmer, more humid environments keep it more robust. So shivering outside in dry winter air after a plunge, especially while mouth breathing, could plausibly raise infection odds.

• 03

  If you are actually sick, skip deliberate cold exposure

  His direct advice: if you feel malaise or fatigue because of a cold, flu or bacterial infection, stay out of the cold. That holds even though regular cold exposure can raise immune markers. He extends the same rule to hard exercise and stressful heat. Warm or hot baths, showers or a gentle sauna are fine, but not saunas hot enough to be a deliberate stressor aimed at heat-shock proteins or heart rate adaptation.

• 04

  Mild symptoms are an edge case: warm up thoroughly if you go ahead

  For a slight sniffle or feeling a bit run down, his first suggestion is the old-fashioned one: take a hot shower and go to sleep. If you are determined to plunge anyway, make sure to fully rewarm afterwards with a hot shower, bath or moderate sauna, and perhaps hot tea.

• 05

  Repeated cold exposure nudges immune markers upward; one session does not

  Across several studies, deliberate cold exposure increases the release and production of various immune molecules and cells, mainly when it is repeated over weeks. Huberman stresses that the effects are modest: in the key study they were trends, not statistically significant changes. Nobody yet knows how those shifts translate into real resistance to a given dose of cold or flu virus, which would be very hard to test.

• 06

  Adrenaline and noradrenaline are the likely link between cold and immunity

  Cold water and deliberate hyperventilation both release epinephrine (adrenaline) and norepinephrine (noradrenaline) in brain and body. Short-term spikes are pro-immune and can activate immune cells and molecules. But chronically high levels, especially repeated late in the day over many days, can reduce the number and efficiency of immune cells. He suggests thinking of 'can cold make me sick?' as 'what happens when I spike adrenaline?'

• 07

  Suppressing symptoms is not the same as beating the infection

  In the PNAS hyperventilation study (below), participants avoided fever and nausea partly because the adrenaline surge suppressed parts of the innate immune response. They still had endotoxin in their bodies; they just were not mounting a fever, which is itself an adaptation that heats up and helps kill an infection. Huberman admits he is 'saying two things at once': the same molecules can strengthen or dampen immunity depending on dose and timing.

• 08

  Rest when sick because sickness behavior is adaptive

  Infection activates brain 'sickness circuits' that push you to move less, curl up, look down and slump. Huberman frames this as a design for healing: the goal when ill is to devote the body's resources to fighting infection. A little gentle walking to circulate blood is probably fine if you are not bedridden.

• 09

  Nasal breathing doubles as an infection barrier

  He recommends nose breathing whenever you are not exercising hard, doing martial arts or talking. Zone 2 cardio and walking are good times to keep the mouth closed. Beyond reasons covered in other episodes, the mouth is a main site of entry for infections.