Poor sleep quality and intermittent hypoxia are linked with elevated blood pressure over time.

WHY IT HAPPENS

Mouth breathing at night can be connected to snoring and sleep apnea. Repeated airway collapses when sleeping triggers stress signals and intermittent drops in oxygen, which can spike blood pressure. When breathing stops during sleep repeatedly, the cardiovascular system shifts into a stressed state.

In Breath, James Nestor documented blood pressure climbing to hypertensive ranges with forced mouth breathing and dropping to normal levels when returning to nasal breathing (1). Clinical studies show patients with obstructive sleep apnea have higher 24‑hour blood pressure versus nasal breathers (2).

Clinical studies back up the link: patients with obstructive sleep apnea—a condition strongly associated with chronic mouth breathing—show higher 24-hour blood pressure compared to nasal breathers.

SOURCES

Nestor, J. Breath: The New Science of a Lost Art (2020). 

Martínez-García et al. JAMA (2013): CPAP reduces 24-h BP in resistant hypertension (HIPARCO).

Becker et al. Circulation (2003): effective CPAP lowers day & night BP by ~10 mmHg. Blood pressure averages were taken over a 24 hour period using the systolic method.

Open-mouth sleep can narrow the airway and increase the likelihood of snoring, disrupting deep sleep.

WHY IT HAPPENS

During sleep, opening the mouth and switching to oral breathing can narrow the pharynx and increase its tendency to collapse. When the upper-airway narrows, the resistance can lead to snoring and airway obstructive events that fragment sleep. (3)

In Breath, James Nestor observedsnoring can reach up to 80 decibels—like a kitchen blender—when the mouth is open at night. Nasal breathing dropped breathing noise to a whisper. (1)

Clinical trials confirm: mouth breathing makes the airway more collapsible and more likely to snore.In sleeping adults, oral breathing increased upper-airway resistance to ~12.4 vs 5.2 cmH₂O·L⁻¹·s with nasal breathing, and raised apnea–hypopnea index (AHI) from ~1.5 to 43 events per hour in the same subjects. (2 & 3)

SOURCES

Nestor, J. Breath: The New Science of a Lost Art (2020).

Fitzpatrick et al. Am J Respir Crit Care Med (2003): oral vs nasal breathing during sleep—oral breathing doubled resistance and raised AHI (apnea–hypopnea index)

Meurice et al. Am J Respir Crit Care Med (1996): mouth opening increases upper-airway collapsibility.

Mouth breathing can dry out saliva, the body’s natural defense against cavities and gum disease.

WHY IT HAPPENS

Saliva helps wash away bacteria and balance mouth pH. Breathing through the mouth reduces saliva, which can leave teeth and gums more vulnerable. Clinical studies in children and teens show mouth breathing raises plaque and gingivitis amounts, even with good hygiene routines.

Late-adolescent mouth-breathers had a 4× higher risk of high Streptococcus mutans counts (a key cavity bacterium) over 6 months even with good hygiene.

In 201 schoolchildren (11–14 yrs), mouth breathing was independently linked withincreased plaque and gingival inflammation, even after controlling for other factors.

SOURCES

Mummolo M. Biomed Res Int (2018): salivary markers & bacteria in mouth-breathers.

Wagaiyu & Ashley. J Clin Periodontol (1991): mouthbreathing & gingival inflammation.

Mouth breathing makes workouts feel harder and less efficient at steady effort.

WHY IT HAPPENS

Oral-only breathing tends to drive faster, shallower breaths which are less efficient in CO₂ exchange and waste energy. Studies show nasal breathing improves efficiency by slowing breathing rate and raises the amount of CO₂ exhaled. 

VE/VCO₂ can be used as an indicator of heart and lungs health where the number tells how many breaths your body needs to blow out the “used air” (carbon dioxide) when you are exercising. A higher VE/VCO₂ means your heart and lungs may be working too hard.

SOURCES

Eser et al. Front Physiol (2024): nasal breathing improved ventilatory efficiency.

Recinto et al. Sports (2017): mouth breathing drove hyperventilation but didn’t increase power.

In children, mouth breathing can change how facial features develop—potentially leading to narrower jaws, longer faces, and smaller airways.

WHY IT HAPPENS

Chronic mouth breathing shifts tongue and jaw posture, rotating the mandible downward and back. Meta-analyses show mouth-breathing kids have steeper mandibular planes, narrower airways, and more tooth crowding. (1)

Meta-analysis of 10 studies: mouth-breathing children had both jaws positioned further back, higher mandibular plane angles (SNGoGn +4.1°), and narrower airway measures (PAS −2.1 mm) (2).

A second meta-analysis found greater mandibular plane angles and facial height in mouth-breathers vs nasal-breathers—consistent with the classic “adenoid facies” pattern.

SOURCES

Zhao et al. BMC Oral Health (2021) meta-analysis: craniofacial changes & airway.

Zheng et al. Exp Ther Med (2020) meta-analysis: facial morphology differences.