A mouth that rests slightly open is common in older age, and it usually reflects several small physical changes adding up rather than one single cause. The lips, jaw, teeth, tongue, neck posture and breathing all help keep a mouth closed, and aging can loosen more than one of them at once. An open mouth can also be an early outward sign of a condition affecting the nerves that control the face, so the pattern around it matters more than the open mouth alone.
How Aging Muscles and Lips Let the Mouth Fall Open
The ring of muscle that closes the lips changes with age. Its outer fibers tighten and stay tense at rest, while the fibers at the lip edge lose their elasticity.1PubMed Central. The Aging Process of Facial Muscles The fat pads that give lips their fullness also shrink considerably over time.2PubMed Central. The Aging Process of Facial Muscles Lips that once rolled outward become flatter and turned inward, leaving less soft tissue to meet and seal.3PubMed Central. The Aging Process of Facial Muscles Keeping the lips together at rest can stop being automatic and start taking effort, effort that drops off when a person relaxes or tires.
The tongue and throat muscles weaken too. The pressure the tongue can press against the roof of the mouth falls noticeably with age, because the muscles above and below the voice box that help hold the tongue and jaw in place tire and weaken.4PubMed Central. Anatomic and physiopathologic changes affecting the airway of the elderly patient: implications for geriatric-focused airway management That weakness can make swallowing harder and raises the chance of food or drink going down the wrong way.5PubMed Central. Anatomic and physiopathologic changes affecting the airway of the elderly patient: implications for geriatric-focused airway management A tongue that rests lower in the mouth also gives the jaw less support to stay closed.
In daily life, the mouth tends to open most when the person is relaxed, watching TV, or dozing in a chair. They can usually close it when asked, which is one clue, among several, that muscle weakness rather than a nerve problem is behind it. The lips may look thinner and turned in, and the corners of the mouth may droop. The change is gradual and even on both sides.
Weakened muscles can hold a position well for a short time but tire over hours, so many families notice the open mouth more in the evening. Illness, poor sleep, or dehydration can make the tiredness, and the open mouth, more noticeable.
A slow loosening of the lips over months or years, equal on both sides, fits wear and tear on the muscles rather than a new illness. A change that appears over days or weeks, or looks different on one side, calls for a medical check rather than an assumption of aging.
Missing Teeth, Bite Collapse and Denture Problems
The back teeth act like pillars that hold the upper and lower jaw at the right distance apart. When lost teeth are not replaced, the jaws can lose their proper position, a change dentists call bite collapse.6ASSSA English. Loss of Vertical Dimension of Occlusion or Bite Collapse: Why the loss of one tooth can lead to the loss of more teeth? Without back-tooth support, the front teeth tend to tip forward and the bite deepens.7Journal of Dental Rehabilitation and Applied Science. Full mouth rehabilitation accompanied by phonetic analysis of a patient with reduction of vertical dimension of occlusion, and inaccurate pronunciation due to numerous tooth loss: a case report Chewing gets weaker, speech can become less clear, the face changes shape, and jaw joint pain can develop.8Journal of Dental Rehabilitation and Applied Science. Full mouth rehabilitation accompanied by phonetic analysis of a patient with reduction of vertical dimension of occlusion, and inaccurate pronunciation due to numerous tooth loss: a case report Lips and jaw that no longer meet in their old positions find it harder to rest closed.
When the jaws close too far, the lower face can look shorter, with the chin rising toward the nose. Deep lines can form at the corners of the mouth, where skin folds and stays moist. The lips may turn inward because the teeth and bone beneath them no longer hold them out.
Dentures help, but fit matters. Losing teeth changes the proportions of the lower third of the face, and complete dentures restore much of its appearance, though not exactly to how it looked with natural teeth.9PubMed. Quantifying the facial proportions in edentulous individuals before and after rehabilitation with complete dentures compared with dentate individuals: A 3D stereophotogrammetry study Wearing complete dentures pushes the upper lip forward by close to a millimeter and fills out the area around the mouth, most noticeably at rest.10PubMed. Facial soft tissue surface changes following complete denture treatment: A comprehensive 3D analysis But dentures set too short, or giving too little lip support, can change the lip line and make the visible red part of the lips smaller.11Journal of Prosthodontic Research. Changes in lip forms on three-dimensional images with alteration of lip support and/or occlusal vertical dimension in complete denture wearers Dentures that have worn down or loosened over years may let the face sag again.
Several signs suggest dentures are part of the problem. The mouth looks sunken, or the chin seems to move closer to the nose. The dentures click, slip, or are often left out. The mouth hangs open mainly when the dentures are out, such as at night. Sore spots or chewing trouble often appear alongside. Slurred s sounds or whistling may point to tooth or denture issues rather than nerves, and avoiding chewy foods suggests weak bite support.
At a dental visit, the dentist checks how far apart the jaws sit when the teeth meet. Old dentures can sometimes be relined or remade at the correct height, and replacing missing back teeth can restore support for the jaw.
Posture and the Forward-Leaning Head
Many older adults develop a stooped, forward-head posture. Changing head posture can shift where the lower jaw sits and how the chewing muscles work.12Physical Therapy Korea. Influence of Forward Head Posture on Electromyography Activity of Hyoid Muscles During Mouth Opening It can also change the position of the small bone in the throat that anchors tongue muscles, and the shape of the face’s profile.13PubMed. Changes in the craniofacial morphology and hyoid bone position in the neutral and forward head posture in healthy individuals: A cross-sectional study A forward or drooping head can therefore tug the jaw down and make an open mouth more likely.
Some of this is visible at home. Watch for the chin pushed forward while sitting in a deep chair or using a phone. Dozing with the head dropped back often lets the jaw fall open. Supportive pillows or a higher-backed chair can keep the head more upright, and raising screens and reading material to eye level helps.
Neck stiffness or pain alongside the posture is worth having assessed. A physical therapist can suggest gentle posture exercises suited to an older person, though posture changes slowly and needs daily practice.
Mouth Breathing and Sleep
Breathing partly through the mouth during sleep becomes more common as people age.14PubMed. Older individuals have increased oro-nasal breathing during sleep People 40 and older are about six times more likely than younger people to spend more than half their sleep breathing partly through the mouth.15PubMed. Older individuals have increased oro-nasal breathing during sleep That link with age held regardless of snoring, weight, sleeping position, or sex.16PubMed. Older individuals have increased oro-nasal breathing during sleep
Sleep apnea is a condition where the throat repeatedly narrows or closes during sleep, briefly stopping breathing. People with sleep apnea spent about 97% of sleep with their mouths open, compared with about 27% for people without it.17PubMed Central. Mouth opening/breathing is common in sleep apnea and linked to more nocturnal water loss The more severe the sleep apnea, the more mouth breathing tends to occur.18PubMed Central. Mouth opening/breathing is common in sleep apnea and linked to more nocturnal water loss Heavy night-time mouth breathing is also linked with losing more body water overnight.19PubMed Central. Mouth opening/breathing is common in sleep apnea and linked to more nocturnal water loss Mouth breathing makes dry mouth worse, and trying to cut it down helps the mouth stay moist.20Friend Family Dentistry. Don’t Suffer From Dry Mouth: 5 Xerostomia Remedies | Friend Family Dentistry
Signs that point to sleep apnea include loud snoring with pauses, gasps, or choking sounds; heavy daytime sleepiness or dozing off while sitting; and morning headaches, dry mouth, or waking very thirsty. A doctor can arrange a sleep study, sometimes done at home.
A quiet, slightly open mouth with steady breathing is usually harmless. Breathing that stops and restarts loudly needs checking. A bed partner can observe it, or a phone recording can.
To ease night-time dry mouth, keep water by the bed and sip through the day. A bedroom humidifier can help. Ask the doctor or pharmacist whether any medicines add to dryness, and treat a blocked nose so breathing through it is easier.
When an Open Mouth Signals Parkinson’s, Stroke or Dementia
People with Parkinson’s disease often lose movement in their face, making it hard to show emotion and speak clearly. They may begin to keep their mouths open and drool.21Health Research Authority. The assessment and treatment of hypomimia in Parkinson’s disease
The fixed, mask-like face of Parkinson’s comes with less blinking and a steady stare. The voice often becomes quieter and softer too, so a soft voice with an open mouth together is more suggestive than either alone.
A stroke or a facial palsy such as Bell’s palsy can weaken lip strength. Common results are drinks leaking from the mouth, drooling, biting the cheek, and food staying in the mouth.22PubMed Central. Training lip force by oral screens. Part 3: Outcome for patients with stroke and peripheral palsy After a stroke, the tongue can be affected as well as the lip muscles.23PubMed Central. Training lip force by oral screens. Part 3: Outcome for patients with stroke and peripheral palsy A sudden droop on one side of the face is an emergency sign of stroke.
In dementia, some people lose the ability to deliberately control movements of the mouth and face even when the muscles work.24PubMed. Buccofacial Apraxia, Oropharyngeal Dysphagia, and Dementia Severity in Community-Dwelling Elderly Patients This loss of control goes with more severe dementia, more disability in daily life, and greater frailty.25PubMed. Buccofacial Apraxia, Oropharyngeal Dysphagia, and Dementia Severity in Community-Dwelling Elderly Patients
Aging changes come on over years and affect both sides evenly. Parkinson’s brings a fixed, expressionless face and slowness, often with tremor. Stroke or palsy is usually sudden and one-sided. Dementia-related changes come with memory and daily-living problems.
Drooling in Parkinson’s and after stroke usually comes from swallowing less often and from weak lip closure, not from making too much saliva. Saliva that isn’t swallowed regularly collects in the mouth and spills over the lips. That is why treatment focuses on swallowing and lip control, and sometimes on medicines that reduce saliva.
Sudden face droop, arm weakness, or slurred speech means calling emergency services immediately. New drooling or coughing while eating deserves a prompt doctor visit, since choking or chest infections can follow swallowing problems.
What Can Help Keep the Mouth Closed
Mouth and face muscle training in older adults increased both lip and tongue strength.26Journal of Dental Hygiene Science. The Effects of Orofacial Myofunctional Training on the Changes of Lip and Tongue Strength in Elderly People The gains were small, so exercises help most when combined with fixing other causes. Oral screen devices held behind the lips have been used to train lip force after stroke and facial palsy.27PubMed Central. Training lip force by oral screens. Part 3: Outcome for patients with stroke and peripheral palsy A dentist or speech therapist can suggest exercises suited to the person.
Common ones to ask about include pressing the lips firmly together and holding for a few seconds, pushing the tongue up against the roof of the mouth, and puffing out the cheeks with the lips sealed. Short sessions daily work better than occasional long ones. They should be gentle, with no pain in the jaw or face, and should stop if the jaw joint clicks painfully. Doing them in front of a mirror or alongside a family member helps the person see they are doing them correctly, and linking them to a habit such as brushing teeth makes them far more likely to continue.
Exercises do little for an open mouth caused mainly by ill-fitting dentures or bite collapse, which need dental correction first. For a person with advanced dementia who can’t follow instructions, they are usually not practical, and comfort-focused care matters more. After a stroke, a therapist should guide the exercises because the weakness may be uneven.
Refitting dentures or replacing missing back teeth restores support for the jaw and lips.28Journal of Dental Rehabilitation and Applied Science. Full mouth rehabilitation accompanied by phonetic analysis of a patient with reduction of vertical dimension of occlusion, and inaccurate pronunciation due to numerous tooth loss: a case report Screening for sleep apnea is worthwhile when mouth breathing comes with snoring and daytime sleepiness. Treatment of Parkinson’s or stroke recovery therapy often includes face and swallowing work.
Start with a dentist if teeth are missing or dentures are old. See a doctor if there is snoring, drooling, tremor, or memory change. A speech and language therapist helps with lip control and swallowing.