How to Prevent & Treat Colds & Flu

Summary

Andrew Huberman explains the biology of the common cold and influenza, detailing how these viruses spread and how the immune system’s three-layered defense system combats them. The episode covers science-supported behavioral protocols and specific compounds to both prevent infection and accelerate recovery. A significant focus is placed on practical, zero-cost strategies that enhance immune function before and during illness.

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Key Takeaways

• Cold virus can survive on surfaces for up to 24 hours; flu virus dies off after approximately 2 hours — the primary route of self-infection is touching your eyes or mouth after contact with contaminated surfaces or people.
• You become contagious ~24 hours before symptoms appear for both colds and flu, and remain contagious until symptoms fully resolve — not just 5–6 days in.
• Nasal breathing is one of the most effective zero-cost strategies to prevent infection — it warms incoming air, maintains nasal microbiome diversity, and activates mucosal defenses.
• Sleep deprivation significantly impairs the innate immune system — even getting 50–75% of your sleep requirement reduces your ability to fight off viruses.
• 2–4 servings of low-sugar fermented foods per day (sauerkraut, kimchi, kefir, kombucha) supports gut microbiome diversity, which is critical for immune function.
• Short-term stress does not necessarily harm immunity — cortisol plays an active role in activating natural killer cells; only chronic stress or stress that impairs sleep is immunosuppressive.
• Exercise of appropriate intensity and duration boosts innate immune activity via the lymphatic system — excessive exercise, however, can suppress immunity.
• The flu shot reduces risk of contracting the season’s dominant flu strain by 40–60% but is ineffective against other strains or cold viruses.
• Caloric restriction over extended periods can compromise innate immune function, though brief intermittent fasting may have modest immune benefits.

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Detailed Notes

What Is the Common Cold?

• “The cold virus” is not a single virus — there are over 160 different serotypes of rhinovirus, categorized under rhinoviruses (named for nasal symptoms).
• Different serotypes have different surface protein shapes, which is why prior antibody production doesn’t protect against new variants — and why we get multiple colds per year.
• Symptoms typically appear 1–2 days after exposure.
• Cold virus particles are approximately 5 microns in size and can spread via sneezing, coughing, and surface contact.
• Surface survival: up to 24 hours on skin, objects, door handles, etc.
• Primary entry route into the body: the eyes, followed by the mouth — skin itself is an effective barrier with antiviral surface chemicals.

What Is the Flu?

• Influenza viruses are categorized as Type A, B, or C, with Type A being the most common and dangerous (e.g., H1N1, which caused the Spanish Flu of 1918–1920, killing 17–50 million people).
• Flu virus classifications (e.g., H1N1) refer to the specific surface proteins expressed on each strain.
• Surface survival: approximately 2 hours — flu transmission is more dependent on direct human-to-human contact or aerosol exposure than surface contact.
• You are most contagious during the 3 days of peak symptoms (fever, coughing, sneezing).
• Like colds, flu is contagious ~24 hours before symptoms appear.

The Flu Shot

• Flu shots are developed each season targeting the most prevalent strains.
• Efficacy: 40–60% reduction in risk of contracting the targeted strain.
• Also shown to reduce symptom severity even if infection occurs.
• Completely ineffective against non-targeted flu strains and cold viruses.

The Three Layers of Immune Defense

1. Physical Barriers

• Skin: a living organ that produces antiviral/antibacterial chemicals on its surface.
• Nasal mucosa: sticky, warm lining that traps and neutralizes viruses; nasal microbiome is the primary first-line antiviral defense site.
• Eyes: surface tears and antibacterial agents actively kill pathogens (the “eye crust” in the morning is defeated bacteria).
• Mouth: mucosal lining with distinct microbiota from nasal passages.
• Primary virus entry points: eyes > mouth > nose via hand-to-face contact.

2. The Innate Immune System

• A fast, non-specific response — doesn’t distinguish between virus types or serotypes.
• Deploys white blood cells: neutrophils, natural killer cells, macrophages.
• Complement system: chemical signals in the blood mark infected cells with “eat me” signals.
• Infected cells release cytokines (e.g., interleukin-1, interleukin-6, TNF-alpha) — these drive inflammation, increased blood flow, and swelling at infection sites.
• Histamines (released from mast cells) contribute to localized heat and swelling (edema).
• Exercise at appropriate intensity activates the innate immune system via the lymphatic system — potentially allowing innate immunity to resolve infection before adaptive immunity is needed.

3. The Adaptive Immune System

• Activates a few days after initial infection; highly specific to the infecting serotype.
• First produces IgM antibodies — a close but imperfect match to the virus surface shape.
• Then refines production into IgG antibodies — highly specific to the exact viral surface profile.
• Generates immunological memory via stem cell populations in bone marrow — enabling rapid antibody deployment upon re-exposure to the same serotype.
• Vaccines work by training the adaptive immune system without full infection.

Behavioral Strategies to Strengthen Immunity

Sleep

• Sleep deprivation — even partial (50–75% of requirement) — significantly impairs innate immune function.
• Aim for however much sleep prevents daytime sleepiness (excluding a normal 10–30 min afternoon dip).

Exercise

• Moderate-intensity, appropriate-duration exercise recruits the lymphatic system and enhances innate immune activity.
• Excessive exercise (e.g., two hard workouts in one day) can suppress immunity and increase susceptibility to infection.

Nutrition

• Caloric deficit over extended periods compromises innate immune function.
• Brief intermittent fasting may modestly support immune function.
• 2–4 servings/day of low-sugar fermented foods (refrigerated sauerkraut, kimchi, kefir, kombucha, yogurt with live cultures) promotes microbiome diversity.
• Fermented foods must contain live cultures — look for refrigerated options.

Stress Management

• Chronic stress impairs immune function — especially when it disrupts sleep.
• Short-term stress (not sleep-disrupting) can enhance innate immunity by elevating cortisol, which activates natural killer cells and cytokine deployment.
• Cortisol is beneficial when elevated in the morning and at appropriate levels — chronically high or chronically low cortisol both impair immunity.

Nasal Breathing

• Nasal breathing is strongly recommended throughout the day (except during speech, eating, or high-intensity exercise).
• Heats incoming air in a way that reduces viral embedding in mucosal lining.
• Maintains diversity of nasal microbiome — the primary antiviral defense barrier.
• Mouth-breathing children and adults show higher rates of upper respiratory infections, including colds and flu.
• Referenced resource: Jaws by Stanford colleagues on nasal breathing and health.

Avoiding Self-Infection

• Studies from Noam Sobel’s lab (Weizmann Institute) show people unconsciously touch their eyes or mouth within ~30 seconds of shaking hands — likely a chemo-signal detection behavior.
• Being conscious of this habit can reduce transmission risk.
• Cold virus survives up to 24 hours on surfaces — hand sanitization after touching shared surfaces is protective.

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Mentioned Concepts

• rhinovirus
• influenza
• [[innate