Cold Exposure, Immunity & REM Sleep — AMA #7 (Huberman Lab)
Summary
In this Ask Me Anything episode, Andrew Huberman addresses whether deliberate cold exposure can cause illness, when to avoid it, and how it interacts with the immune system. He explains the nuanced relationship between cold-induced epinephrine and norepinephrine release and immune function, offering clear guidance on protocols for both healthy individuals and those feeling unwell.
Key Takeaways
- Deliberate cold exposure of 1–10 minutes does not directly cause colds or infections, provided you warm up properly afterward.
- Cold, dry air — especially combined with mouth breathing — can thin mucosal linings and increase susceptibility to viral and bacterial infections.
- If you are sick (malaise, fever, fatigue), avoid deliberate cold exposure, intense exercise, and extreme heat exposure — rest and conserve your body’s resources.
- Repeated cold exposure (e.g., 3x/week for 6 weeks) shows trends toward increased immune cell counts and immune markers.
- Epinephrine and norepinephrine released during cold exposure can be pro-immune in the short term but immune-suppressive if chronically elevated.
- Cyclic hyperventilation (Wim Hof/tummo breathing) triggers similar norepinephrine/epinephrine release and can suppress symptomology from bacterial infections — but this suppression is not the same as fighting off infection.
- Nasal breathing is strongly preferred over mouth breathing as it protects mucosal barriers against infection entry.
- If feeling slightly run down but determined to do cold exposure, warm up thoroughly afterward — hot shower, hot tea, or sauna at a non-stressful temperature.
Detailed Notes
Can Deliberate Cold Exposure Make You Sick?
- Cold exposure itself (1–10 minutes in cold water, followed by warming up) does not directly cause colds or infections, assuming the water is clean.
- The risk comes from the environment after cold exposure: if you remain in cold, dry air while shivering, especially while mouth breathing, mucosal defenses weaken.
- Cold, dry air reduces the robustness of the mucosal lining in the nose and throat — the primary physical barrier against viral and bacterial entry.
- Warmer, more humid environments support a stronger mucosal barrier.
Should You Do Cold Exposure When Sick?
| Condition | Recommendation |
|---|---|
| Feeling good | Do cold exposure; warm up afterward |
| Slightly rundown / mild sniffle | Optional — if you do it, warm up very well after; hot tea recommended |
| Clear illness (malaise, fever, fatigue) | Avoid cold exposure, hard exercise, and stressful heat exposure |
- When ill, the body activates sickness circuits in the brain that promote stillness, curled posture, and rest — these are adaptive responses designed to direct resources toward healing.
- Light movement (e.g., short walks) is acceptable if not severely ill, to maintain circulation.
Cold Exposure and Immune Function
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Study referenced: “Immune System of Cold Exposed and Cold Adapted Humans”
- Protocol: 14°C (57.2°F) water, 1 hour exposure, 3x/week for 6 weeks
- Results: Single exposure showed no significant immune change; repeated exposure showed trends toward increased IL-6, T lymphocytes, T helper cells, T suppressor cells, and activated T and B lymphocytes
- Note: These were trends, not statistically significant findings
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Mechanism: Cold exposure releases epinephrine and norepinephrine into both brain and body
- Short-term elevation → pro-immune (activates immune cells and molecules)
- Chronic elevation, especially late in the day → immune-suppressive (reduces immune cell efficiency)
Wim Hof Breathing and Immune Response
- Study referenced: “Voluntary Activation of the Sympathetic Nervous System and Attenuation of the Innate Immune Response in Humans” (PNAS)
- Participants injected with E. coli endotoxin experienced flu-like symptoms (fever, vomiting, diarrhea)
- Those who performed cyclic hyperventilation beforehand experienced significantly reduced symptoms
- Mechanism: Norepinephrine/epinephrine release suppressed certain arms of the immune response, reducing symptomology (e.g., fever) — but not by eliminating the infection
- Fever is itself an adaptive immune tool (raises body temperature to kill pathogens)
Nasal Breathing as Immune Defense
- Nose and mouth are the primary entry points for viruses and bacteria (eyes are secondary)
- Nasal breathing filters pathogens through mucous lining before they reach the respiratory tract
- Recommendation: Breathe through the nose whenever possible — during low-intensity exercise (Zone 2 cardio), walking, rest
- Mouth breathing is acceptable during hard exercise, martial arts, or talking
Mentioned Concepts
- deliberate cold exposure
- epinephrine / adrenaline
- norepinephrine / noradrenaline
- cyclic hyperventilation
- Wim Hof breathing
- tummo breathing
- innate immune system
- adaptive immune system
- nasal breathing
- mucosal immunity
- sympathetic nervous system
- heat shock proteins
- interleukin-6 (IL-6)
- T lymphocytes
- sickness behavior