10 Reasons Your Sleep Is Getting Worse — And the One Thing That Actually Fixes It

Core body temperature must fall 2–3 degrees Fahrenheit to trigger sleep onset. This cooling process begins about two hours before sleep and is one of the primary physiological signals that tells the brain it is time to rest. When this cooling is disrupted — by stress, inflammation, or a warm environment — sleep onset is delayed and deep sleep is reduced.

The mechanism is well-established: as core temperature drops, the brain interprets the shift as a cue to begin the sleep cascade. Without that drop, the brain stays in a state of physiological alertness even when the body is tired. A sauna session followed by natural cooling provides exactly this thermal cue.

Source: Murphy & Campbell, "Nighttime drop in body temperature: a physiological trigger for sleep onset?" — Sleep, 1997

Cortisol follows a circadian rhythm — it should be at its lowest point in the late evening and during the first half of sleep. Research published in PMC found that patients with insomnia show elevated cortisol specifically in the evening and at sleep onset, suggesting that unresolved stress is a direct physiological barrier to sleep — not just a psychological one.

This distinction matters. Cortisol elevation is not a feeling of being stressed. It is a hormonal state that persists regardless of how calm you believe you are. The body needs a physiological mechanism to clear it, not just a mental one.

Source: Hirotsu et al., "Interactions between sleep, stress, and metabolism" — PMC / Clinics, 2015

A large meta-analysis published in PMC found that sleep disturbance is associated with inflammatory disease risk and all-cause mortality. The relationship is bidirectional: inflammation disrupts sleep, and poor sleep worsens inflammation. This cycle is one of the most underdiagnosed contributors to chronic insomnia.

People treat the symptom — the inability to sleep — without addressing the underlying inflammatory state that is preventing the body from entering deep sleep in the first place. Infrared heat has been shown to reduce systemic inflammatory markers, addressing the root rather than the symptom.

Source: Irwin et al., "Sleep disturbance, sleep duration, and inflammation" — PMC / Biological Psychiatry, 2015

Slow wave sleep — Stage 3 NREM — is the phase where the body repairs tissue, consolidates memory, and regulates hormones. A review published in PMC found that sauna bathing increased the amount of slow wave sleep by over 70% in the first two hours.

Most people never experience this level of deep sleep because they have no physiological trigger for it. The body needs a specific thermal cue — a drop in core temperature following a period of elevated heat — to reliably enter and sustain slow wave sleep.

Source: Laukkanen et al., "The multifaceted benefits of passive heat therapies for extending the healthspan" — PMC / Temperature, 2024

The parasympathetic nervous system — the "rest and digest" state — must dominate before and during sleep for the body to fully recover. Research from Ahokas et al. found that post-exercise infrared sauna sessions shift autonomic balance toward parasympathetic dominance, increasing HRV.

Without a reliable mechanism to shift the nervous system out of sympathetic dominance, the body remains in a low-grade alert state even during sleep — reducing sleep quality without the person being aware of why.

Source: Ahokas et al., "Effects of repeated use of post-exercise infrared sauna on neuromuscular performance" — PMC / Temperature, 2025

A study published in the Journal of Athletic Training found that whole-body red light irradiation significantly improved sleep quality and increased melatonin levels in elite female basketball players. Melatonin is the primary hormone that signals the body it is time to sleep — and most people’s evening environments actively suppress it.

Blue light from screens delays melatonin onset by up to 90 minutes. Red light at 660nm does the opposite — it reinforces the body’s natural sleep signal without supplementation. The Solara’s built-in red light panels deliver this wavelength as part of every session.

Source: Zhao et al., "Red Light and the Sleep Quality and Endurance Performance of Chinese Female Basketball Players" — PMC / Journal of Athletic Training, 2012

Unresolved physical tension keeps the sympathetic nervous system in a low-grade activated state, making it physiologically harder to fall into deep sleep. A peer-reviewed study by Mero et al. found that far-infrared sauna bathing significantly reduced muscle soreness and improved recovery from both strength and endurance training sessions.

This is particularly relevant for anyone who exercises in the evening, works a physically demanding job, or carries chronic tension from long hours at a desk. The body cannot fully enter recovery mode while it is still processing unresolved physical stress.

Source: Mero et al., "Effects of far-infrared sauna bathing on recovery from strength and endurance training" — PMC / SpringerPlus, 2015

A comprehensive review published in PMC found that among factory workers exposed to heavy metals, increasing serum concentrations were directly associated with declining sleep quality. Environmental toxins — including heavy metals and airborne pollutants — have a measurable impact on sleep architecture.

Sweating is one of the body’s primary detoxification pathways. A separate PMC review confirmed that sweating — particularly through sauna — supports the excretion of heavy metals including lead, mercury, arsenic, and cadmium, reducing the toxic burden the body must process during sleep.

Source: Liu et al., "Environmental exposures and sleep outcomes" — PMC / Environmental Health Perspectives, 2020  ·  Sears et al., "Arsenic, Cadmium, Lead, and Mercury in Sweat" — PMC, 2012

The brain relies on consistent environmental and physiological cues to initiate the sleep cascade. Research on thermoregulation and sleep confirms that the likelihood of NREM onset is highest when core temperature is at its steepest rate of decline — a state that can be reliably induced by a structured pre-sleep heat session.

Without a reliable pre-sleep routine that lowers cortisol, drops core temperature, and activates the parasympathetic system, sleep onset becomes inconsistent. A structured infrared session in the evening addresses all three simultaneously — and the body learns to associate the thermal cycle with sleep over time.

Source: Harding et al., "The Temperature Dependence of Sleep" — PMC / Current Opinion in Physiology, 2020

Most sleep interventions — melatonin supplements, white noise, sleep masks — address surface-level symptoms without touching the underlying physiology. They can help at the margins, but they do not move the needle on the root causes: elevated cortisol, poor thermoregulation, chronic inflammation, and insufficient parasympathetic activation.

The research reviewed across all ten reasons above is consistent on this point. Addressing the system — not the symptom — is what produces lasting sleep improvement. The question is not whether the physiology matters. It is whether you have a tool that actually addresses it.

Source: Harding et al., "Sleep and thermoregulation" — PMC / Current Opinion in Physiology, 2019