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

Episode Summary

Executive Summary: Andrew Huberman answers whether deliberate cold exposure can make you sick and whether it should be used when already ill. He argues cold exposure itself doesn’t directly cause colds, but cold, dry environments and mouth breathing can increase infection risk. He recommends avoiding cold/heat/exercise stress when sick, while noting repeated cold exposure may modestly enhance immune markers via adrenaline-related mechanisms.

Main Topics: Can deliberate cold exposure cause illness? (Priority: 5/5): Huberman distinguishes between cold exposure itself and the environmental conditions around it. Brief cold exposure followed by warming up is unlikely to directly cause a cold, but cold, dry air can increase susceptibility to respiratory infections. When to avoid cold exposure (Priority: 5/5): If someone already has a cold, flu, malaise, or a bacterial infection, he advises avoiding deliberate cold exposure and other stressful challenges, favoring rest and gentle recovery instead. Immune effects of repeated cold exposure (Priority: 4/5): He reviews studies suggesting repeated cold exposure may increase immune markers over time, though effects are modest and not proof of direct protection against specific infections. Role of adrenaline and norepinephrine (Priority: 5/5): Huberman explains that cold exposure and hyperventilation raise epinephrine/norepinephrine, which can be pro-immune acutely but potentially suppressive if chronically elevated. Wim Hof-style breathing and immune response (Priority: 4/5): He cites a PNAS study showing cyclic hyperventilation reduced symptoms after endotoxin exposure, illustrating how sympathetic activation can alter immune and symptom responses. Nasal breathing as a protective habit (Priority: 3/5): He emphasizes nasal breathing when possible because the nose is a key barrier to pathogens and mouth breathing may increase exposure risk, especially in cold, dry air. Premium channel and research funding (Priority: 2/5): The episode also promotes the premium subscription model, which supports the podcast and funds human research, with a dollar-for-dollar match from the Tiny Foundation.

Key Arguments: Deliberate cold exposure does not appear to directly cause colds if it is brief and followed by rewarming; the bigger risk is cold, dry air plus mouth breathing. Cold, dry environments can thin and dry mucosal linings in the nose and throat, weakening a primary barrier against viral and bacterial entry. If a listener is already sick or feeling malaise, cold exposure, heat stress, and hard exercise should generally be avoided so the body can focus on recovery. Repeated cold exposure may increase immune markers, but the evidence is mostly trend-level and does not prove reduced infection rates. Cold exposure and cyclic hyperventilation both increase norepinephrine/epinephrine, which can enhance immune activity acutely but may be harmful if chronically elevated. The Wim Hof breathing/endotoxin study suggests sympathetic activation can reduce symptom severity even when exposure to inflammatory stimulus still occurs. Nasal breathing is preferred whenever possible because the mouth is a major entry point for pathogens and mouth breathing can worsen drying in cold air.

Data Points: Typical deliberate cold exposure duration: 1-3 minutes, sometimes 5-6 minutes, up to 10 minutes for experienced users - Huberman describes common practice and cautions against jumping straight to long exposures. Cold exposure study water temperature: 14°C (57.2°F) - In the cited study on immune system effects of cold exposure. Cold exposure study duration: 1 hour - Participants were exposed to 14°C water for an hour in the older study. Repeated exposure frequency: 3 times per week - The cited study examined repeated deliberate cold exposure over six weeks. Repeated exposure period: 6 weeks - Timeframe over which immune marker trends were observed. Immune markers observed: IL-6, T lymphocytes, T helper cells, T suppressor cells, activated T and B lymphocytes - Markers that trended upward with repeated cold exposure. Breathing repetitions in Wim Hof-style protocol: About 25 cycles - Huberman describes cyclic hyperventilation used in the PNAS study. Premium subscription cost: $10 per month - Price for the Huberman Lab premium channel. Annual subscription cost: $100 upfront - One-time payment for a 12-month subscription.

Pivotal Quotes: "if you are feeling good to great, do your deliberate cold exposure." — Andrew Huberman: Core recommendation for when cold exposure is appropriate. "if you are sick, stay out of deliberate cold exposure." — Andrew Huberman: Direct guidance for listeners who are already ill. "keep that mouth shut unless you need to talk." — Andrew Huberman: Advice emphasizing nasal breathing as a protective habit.

Implications: Listeners should separate cold exposure itself from the conditions around it: brief cold exposure is usually fine when healthy, but illness calls for rest. The broader takeaway is that stressors can help or hurt depending on dose, timing, and context.