For many, night often brings an unwelcome surge in seasonal allergy symptoms. Sneezing, congestion, and itchy eyes intensify after sunset, disrupting sleep. This article explores the physiological rhythms, environmental conditions, and allergen behaviors that explain why allergies frequently worsen at night.
The Body’s Internal Clock
The human body operates on a roughly 24-hour cycle known as the circadian rhythm, which profoundly influences biological processes, including immune system responses. Histamine, a chemical released during allergic reactions, naturally exhibits a circadian rhythm, with levels often peaking between midnight and 4 AM. This increased histamine production can intensify symptoms like sneezing, itching, and congestion.
Cortisol, a hormone with anti-inflammatory properties, also follows a predictable daily pattern. Levels typically peak in the morning and reach their lowest point around midnight. This natural decline in cortisol at night reduces the body’s ability to suppress inflammation and allergic reactions. The combination of elevated histamine and reduced cortisol creates a physiological environment conducive to heightened allergic responses during sleep.
Environmental Factors in the Bedroom
The bedroom environment plays a significant role in exacerbating nighttime allergy symptoms. As individuals spend extended periods in their bedrooms, often with windows closed, indoor allergens become more concentrated. Common indoor allergens like dust mites and pet dander accumulate in bedding, mattresses, and upholstered furniture. Direct and prolonged contact with pillows can lead to increased exposure to these accumulated allergens.
Temperature and humidity levels within the bedroom also contribute to allergen proliferation. Dust mites thrive in warm, humid conditions, preferring relative humidity between 70% and 80% and temperatures between 68 and 77°F (20 to 25°C). If humidity drops below 50%, dust mites dehydrate and die, but their remains can still cause allergic reactions. Mold growth, another common indoor allergen, is also encouraged by damp, warm environments, especially in less ventilated areas or rooms adjacent to bathrooms.
Allergen Behavior After Dark
The behavior and concentration of outdoor allergens, particularly pollen, change significantly after sunset. During the day, warm temperatures and wind carry pollen high into the atmosphere. As temperatures drop and wind speeds decrease in the evening, pollen-laden air descends, causing pollen to settle closer to the ground.
Pollen concentrations can become higher at ground level, where people sleep, especially if windows are open. While overall pollen counts might be lower at night compared to peak daytime levels, the localized concentration at breathing height can trigger or worsen symptoms. Pollen can also cling to hair, skin, and clothing, transferring to bedding and increasing exposure throughout the night.