Optimal Indoor Temperature and Humidity: A Scientific Approach

Optimal Indoor Temperature and Humidity: A Scientific Approach

Indoor climate is often a topic of debate — from household discussions to professional settings. Some advocate for keeping the space cool and humid year-round. However, personal opinions and habits do not always align with scientific evidence.

Recent research (source) and meta-analyses (meta-analysis) provide a comprehensive understanding of how temperature and humidity impact not just comfort, but also health, disease risk, and cognitive performance.

Let’s break down what the science says.

1. Air Temperature: Why 22–24 °C Matters

The temperature range of 22–24 °C is considered optimal for indoor environments, especially in temperate and cold climates.

• Above 26 °C: Studies indicate an increase in complaints about fatigue, difficulties in concentrating, feelings of depression, and a measurable decline in cognitive functions (source). Long-term exposure to such temperatures can impair work productivity and mental well-being.

• Below 18 °C: On the other hand, maintaining indoor temperatures lower than 18 °C is associated with a heightened risk of cardiovascular diseases (source) and respiratory illnesses (source). This risk arises due to vasoconstriction — the narrowing of blood vessels (source) that occurs even with moderately cool air inhalation (source).

Thus, simply adding a sweater is not a sufficient solution; the inhaled air itself influences physiological responses critical to health.

2. Air Humidity: Balancing Between 40–60%

Maintaining proper indoor humidity is just as vital as temperature control.

• Optimal Range: The ideal relative humidity for most indoor spaces is between 40% and 60% (source). For individuals prone to allergies or asthma, maintaining humidity closer to 50% is recommended (source).

• Low Humidity Risks: When humidity drops below 30%, the mucociliary clearance of the respiratory system — the mechanism that traps and expels pathogens and pollutants — becomes impaired (source). This increases vulnerability to infections and leads to symptoms like dry eyes, skin irritation, and general fatigue.

• High Humidity Risks: Excess moisture in the air creates a breeding ground for mold and dust mites, two of the most powerful indoor allergens. Overly humid conditions can worsen asthma, allergies, and other respiratory conditions.

3. Infectious Disease Transmission: The Role of Humidity

Humidity levels also significantly impact the survival and transmission of airborne viruses.

• In environments with low humidity, droplets expelled by coughing, sneezing, or talking evaporate quickly, allowing viral particles to remain airborne for longer periods. This increases the risk of viral transmission, including for pathogens like influenza and SARS-CoV-2 (source).

• Higher humidity, within the optimal range, facilitates quicker inactivation of viruses and encourages aerosol particles to settle out of the air more rapidly, reducing the likelihood of inhalation by others.

Thus, maintaining proper humidity is a proactive way to lower infectious risks indoors.

4. Productivity and Cognitive Function

Indoor environmental conditions do not just affect health — they directly influence mental performance and work productivity.

• Optimal conditions (22–24 °C and 40–60% RH) are associated with maximal cognitive functioning (source). Memory, attention span, speed of thought, and reaction times are all sharper in this zone.

• Deviations from the optimal range — whether higher or lower temperature and humidity — lead to a measurable decline in concentration, decision-making speed, and problem-solving accuracy (source).

This insight is particularly important for workspaces, educational settings, and home offices aiming to maximize performance.

5. Final Thoughts: A Rational Approach to Indoor Climate

While short-term exposure to heat or cold — such as sauna use or cold water immersion — can be beneficial for resilience training and health optimization, chronic underheating or overheating indoor spaces for the sake of energy savings is counterproductive (source).

Similarly, striving for humidity levels above 60% is unnecessary and potentially harmful. Humans evolved to thrive in environments with moderate humidity — not in the wet, mold-friendly conditions favored by fungi.

Conclusion: If your goal is to support your immune system, enhance your mental clarity, and feel comfortable daily, maintaining an indoor temperature between 22–24 °C and humidity between 40–60% is a scientifically validated foundation.