Winter often brings noticeable dryness in the air, a sensation directly related to the amount of moisture, or humidity, present in the atmosphere. Understanding the scientific principles behind this shift explains why indoor environments become particularly arid during colder months.
Understanding Dry Winter Air
Winter air feels dry because cold air holds significantly less moisture than warm air. This involves two key measurements: absolute humidity, the actual mass of water vapor in a given volume of air, and relative humidity, the percentage of moisture compared to the maximum amount it can hold at that specific temperature.
When frigid outdoor air, with minimal water vapor, enters a heated indoor space, its temperature rises considerably. Though the absolute amount of water vapor remains the same, its capacity to hold moisture increases with temperature. This leads to a sharp decrease in relative humidity. For example, outdoor air at 20°F with 80% relative humidity might drop to about 15% when heated to 70°F indoors, creating a very dry environment. Indoor heating systems further exacerbate this effect by continuously warming incoming cold air without adding moisture.
Effects of Low Humidity
Low humidity levels can impact both human health and household items. For individuals, dry air often leads to symptoms such as parched skin, chapped lips, and irritation in the nasal passages and throat. This dryness can also make eyes feel itchy and irritated.
Beyond general discomfort, dry air can worsen existing respiratory conditions like asthma and bronchitis, as it dries out the fluid that hydrates bronchial tubes, making airways susceptible to irritation. Studies indicate that viruses, including those causing the common cold and flu, may survive and spread more readily in low humidity environments. Homes can also suffer from prolonged exposure to dry air, which may cause wood furniture, flooring, and musical instruments to shrink, crack, or warp.
Strategies for Comfort
Mitigating the effects of dry winter air often involves increasing moisture in indoor environments. Humidifiers are effective devices that add water vapor into the air, with common types including cool mist (ultrasonic, evaporative) and warm mist (steam vaporizers). Maintaining indoor humidity levels between 30% and 50% is recommended for optimal comfort and health. Regular cleaning of humidifiers is necessary to prevent the buildup of bacteria or mold.
Alongside mechanical solutions, personal practices can enhance comfort. Consistent hydration helps the body maintain moisture. Applying thick, oil-based moisturizers frequently, especially after bathing, helps to seal moisture into the skin. Simple home methods like air-drying laundry indoors or placing bowls of water near heat sources can also contribute small amounts of moisture to the air.