EXTERNAL PHYSIOLOGICAL STRESS FACTORS OR ENVIRONMENTAL STRESS FACTORS 
These factors are related to the environmental condition. For a flight deck, they might include:

• Extreme Temperatures. A generally pleasant temperature for individuals wearing regular clothing is approximately 20°C. When it goes beyond 30°C, there's a rise in heart rate, blood pressure, and perspiration. However, below 15°C, people start feeling uncomfortable and may experience reduced sensation and control in their hands, particularly for precise muscle actions.
• Noise. Intense noise (over roughly 90 dB) disrupts performance, resulting in concentration disruption and deterioration of information retention in working memory. The flight crew errors are increased.
• Vibration. Vibration can impact the entire body or specific parts. Any vibration induces fatigue and can influence visual and motor performance, resulting in discomfort. The vibration's frequency determines the affected body parts, and its intensity governs symptom severity.
• Low humidity. A modern aircraft's air conditioning draws external air through the engine's compressor. At typical airline altitudes, temperatures range from -30°C to -55°C with extremely dry air (5% humidity). Humans prefer comfort at 40% to 60% humidity, but lower humidity leads to discomfort due to drying of nose and throat membranes.

Note: All the factors mentioned in the answers might be considered as environmental stress factors. However, we need to choose the most common ones in the cockpit.