In 1918, countless nurses cared for patients during the influenza pandemic – often with little more than water, soap, and discipline. Their quiet professionalism has shaped what prevention can achieve in everyday life, a lesson more relevant than ever: Those who recognize early warning signs and implement simple, evidence-based steps can not only mitigate winter illnesses but often stop them in time, preserving energy, focus, and performance.

Winter illnesses like influenza, colds, and other respiratory infections are more likely to spread when we are indoors and the air is dry. Dry air causes the mucosal barriermoist protective layer in the nose and throat that traps pathogens to dry out, making it easier for viruses to enter. An underappreciated early sign is an increase in the resting heart rateheartbeats per minute in a relaxed state – it is sensitive to the onset of inflammatory processes. Moreover, relative humidityproportion of water vapor in the air influences how well viruses survive and how effectively our defenses work. For high performers, early detection means less absenteeism, more stable training and work cycles, and better recovery.

What happens when early signs are ignored? An elevated resting heart rate and dry mucous membranes increase the likelihood that viruses will spread and symptoms will emerge. Studies show that moderate humidity reduces the viability of many pathogens, while excessively dry air can facilitate infections ^[1]. Additionally, excessive alcohol consumption increases susceptibility to lung infections because central immune cells in the lungs are weakened ^[2]. Conversely, consistent handwashing among the population reduces the frequency of respiratory infections – a simple yet powerful lever for fewer sick days and more performance reserve ^[3].

Several strands of research converge to form a clear picture. First: Wearable data can signal infections before symptoms appear. In a controlled study with experimental influenza exposure, millions of physiological data points were analyzed; changes in heart rate and blood pressure occurred early and allowed for the prediction of infection two days before significant symptoms appeared ^[4]. For everyday life, this means: A personalized resting heart rate baseline is a useful monitoring tool. Second: Humidity has a double effect – it influences the survival of pathogens and the integrity of our mucous membranes. A review suggests that a relative humidity of about 40–60% minimizes the transmissibility of many pathogens ^[1]. However, the evidence from intervention studies is more heterogeneous: A systematic review found mixed effects on dryness symptoms and uncertain indications of reduced absenteeism, pointing to the importance of proper implementation and contextual factors ^[5]. Third: Behavior matters. A large-scale, internet-based handwashing promotion program significantly reduced the rate of respiratory infections in a real-world setting – an impressive testament that small habits can lead to large systemic effects ^[3].

- Establish a 20-second handwashing ritual with soap and water after public contact (public transport, meetings, gym). A practical hack: Place soap at the entrance of your home so that “hands first, then phone” becomes an automatic routine ^[3].
- Maintain indoor air between 40-60% relative humidity. Use a hygrometer; opt for evaporative or steam humidifiers and clean the devices weekly. This reduces virus survival and protects mucous membranes; also ensure good ventilation to avoid “stuffiness” ^{[1] [5]}.
- Track your resting heart rate daily at the same time (e.g., in bed in the morning). If it rises 3-5 beats above your usual baseline and you feel “off,” reduce training intensity, prioritize sleep, and monitor symptoms for 24-48 hours – often, you can catch infections before they slow you down ^[4].
- Significantly limit alcohol, especially on consecutive winter evenings. Aim for alcohol-free weekdays as the standard. This keeps lung immune function sharp – important for quick pathogen defense ^[2].

The next wave of smart prevention combines behavioral routines with personalized data: hand hygiene, controlled humidity, and resting heart rate tracking as daily micro-interventions. In the coming years, wearables are likely to predict infection risks even more precisely and buildings will automatically maintain health-optimized humidity. Those who start today are building a robust, data-informed immune system for a strong winter.