Atopic dermatitis, commonly known as eczema, is a chronic inflammatory skin condition characterized by dry, itchy, and irritated patches. For many, the most distressing symptom is the intense increase in itching, known as nocturnal pruritus, that occurs at night. This nighttime exacerbation is driven by a complex interplay of internal biological processes and external environmental factors. Understanding the multi-factorial nature of this nocturnal itch is crucial for managing the cycles of discomfort and sleep loss that severely impact quality of life.
Circadian Rhythms and Immune Activity
The body’s internal 24-hour clock, or circadian rhythm, heavily influences the biological mechanisms that regulate inflammation and itch. One significant factor is the natural fluctuation of cortisol, an anti-inflammatory hormone. Cortisol levels peak in the early morning and gradually decline throughout the day, reaching their lowest point during the evening and night. This nightly drop in the body’s natural anti-inflammatory agent leaves the skin’s inflammatory response less suppressed, allowing the underlying eczema to flare up more intensely.
The body’s core temperature undergoes a slight increase in the evening, a process that helps facilitate the onset of sleep. This rise in temperature increases blood flow to the skin’s surface, a change that warms the skin and makes the nerve endings responsible for transmitting itch signals more reactive. As these nerve endings become more sensitive to stimuli, the sensation of pruritus is amplified.
The immune system also follows a circadian rhythm, resulting in a shift in the concentration of inflammatory chemicals known as cytokines. The release of pro-inflammatory cytokines is often elevated during the nighttime hours. These signaling molecules intensify the inflammatory response in the skin, contributing directly to the increased redness, irritation, and itch sensation experienced during sleep. This coordinated biological shift—lower cortisol, warmer skin, and elevated inflammatory mediators—drives the nocturnal worsening of eczema.
Environmental Factors and Skin Hydration
While internal biology sets the stage for nocturnal itching, the immediate sleeping environment and the state of the skin barrier play a major role in triggering the sensation. The skin, especially compromised eczematous skin, naturally loses more moisture to the environment at night through a process called Transepidermal Water Loss (TEWL). This process is the passive evaporation of water from the skin’s surface, and the rate of loss increases during sleep.
The already impaired skin barrier in eczema sufferers cannot effectively retain moisture, meaning the increased TEWL leads to rapid dehydration of the skin. This dryness causes the skin to become tight, sensitive, and more prone to irritation, which directly fuels the itch. A dry sleeping environment, often created by central heating or air conditioning, exacerbates this problem by drawing moisture away from the skin even faster.
The bedding itself can introduce irritants that worsen the condition when held against warm skin for extended periods. Residual chemicals from harsh laundry detergents or fabric softeners can cause contact irritation. Certain materials, like wool or tightly woven synthetic fabrics, can create friction or cause overheating, which increases skin warmth and further stimulates the itch receptors. These environmental and hydration issues compound the biological predisposition to itchiness.
The Cycle of Sleep Loss and Scratching
The final component of nocturnal pruritus is the psychological and behavioral feedback loop. During the day, constant distractions from work, conversation, and activities help suppress the perception of the itch sensation. Once the body is at rest and the mind is quiet, this distraction is removed, causing the individual to focus intensely on the now-amplified sensation.
As a person drifts off to sleep, their conscious control over their body movements is significantly lowered. This reduced inhibition allows for unconscious scratching, often without the individual even fully waking up. This reflexive scratching physically damages the already fragile skin barrier, creating micro-tears and releasing more inflammatory mediators into the tissue.
The resulting damage further intensifies the inflammation and subsequent itch, perpetuating the vicious “itch-scratch cycle” that is characteristic of eczema. The continuous sleep disruption caused by the itch leads to poor sleep quality, which in turn elevates stress hormones and lowers the overall threshold for sensing pain and itchiness the following day. This creates a challenging cycle where poor sleep worsens the skin, and the worsening skin prevents restorative sleep.