Dry mouth in the morning: why do I wake up with a dry mouth?

Saliva flows constantly during the day and increases when you eat and speak. During sleep, however, it almost stops. Colin Dawes, one of the leading names in saliva research, writes in his review in the journal of the American Dental Association that the flow of saliva falls to a negligible level during sleep and that the protective effects of saliva are lost during this time. That is why everyone may wake up in the morning with a somewhat drier mouth. The problem is when this dryness becomes marked and uncomfortable every morning and carries on during the day too.

The commonest cause is breathing through the mouth. The NHS lists breathing through the mouth at night among the main causes of a dry mouth, and writes that this happens when the nose is blocked or you sleep with your mouth open. Air passing through the mouth evaporates the saliva, which is already scarce. A study in New Zealand measured this with a sensor placed on the palate side of the upper front teeth of 10 healthy volunteers: the pH in the mouth averaged 7.3 during the day and 7.0 in normal sleep, but fell to 6.6 in sleep where they were forced to breathe through the mouth with a nose clip, and the drop lasted longer. The researchers state that this may play a part in tooth erosion and decay; the study is small and did not directly measure the effect on the teeth.

The reason for sleeping with the mouth open is often the nose. Allergic rhinitis, sinusitis, enlarged adenoids, a bent nasal septum or a cold block the nose, and the body switches to breathing through the mouth. It is also worth remembering that a blocked nose that persists on one side only can have a dental cause. If your nose is blocked during the day too, the solution to morning dryness lies not in the mouth but in the nose.

Morning dryness is a little-known sign of sleep apnoea. The NHS defines sleep apnoea as breathing stopping and starting during sleep; it lists snoring, waking up gasping or choking, waking often, excessive tiredness during the day and morning headaches among the symptoms. In a study in Israel with 668 people referred for a sleep test because of snoring and 582 adults attending a general health check, waking up with a dry mouth almost every morning was reported by 31.4% of those with sleep apnoea, 16.4% of those who only snored and 3.2% of the control group; the rate rose with the severity of the apnoea. In a 2024 study of 1,291 adults in Beijing too, morning dry mouth was more common in those at high risk of apnoea.

In sleep apnoea, the dryness is not just a feeling; it can be measured. In 30 sleep apnoea patients in Moscow diagnosed with a sleep test, morning dryness was present in 60% of those with mild apnoea, 72.7% with moderate apnoea and 88.9% with severe apnoea; as the apnoea became more severe, the amount of saliva decreased and the saliva became more acidic. This is a small study, but the direction is the same as in the others. What it means in practice: in someone who snores and wakes up with a dry mouth every morning, the problem may not lie only in the mouth. The NHS writes that, if not treated, sleep apnoea can increase the risk of high blood pressure, stroke, type 2 diabetes and heart disease.

Medicines can markedly increase morning dryness, especially those taken in the evening. The NHS lists medicines among the main causes of a dry mouth and recommends checking the leaflet; but it also stresses not stopping a prescribed medicine without talking to a doctor. Drinking too little water, sweating a lot or becoming dehydrated during illness, anxiety, smoking, and alcohol and caffeine taken in the evening are also factors that increase dryness. Dryness that carries on during the day too, or comes with dry eyes or needing to pass urine often, suggests a condition such as diabetes or Sjögren's syndrome; in this case the NHS recommends seeing a GP.

Dryness at night has a cost for oral health. Dawes writes that saliva protects against decay, acid wear (erosion), fungal infection and irritation sores in the mouth, that it clears sugar and acid from the mouth, and that it carries minerals that repair tooth enamel. This protection already drops during sleep; when the mouth stays open, it weakens even more. Dawes's practical conclusion is clear: the most important brushing of the day is the one just before bed. Drinking something sugary or acidic after going to bed turns the unprotected hours into the riskiest time for decay.

For people with dentures and implants, the night matters especially. With a dry mouth, the NHS recommends not sleeping in dentures and taking dentures out at night to prevent oral thrush. In a systematic review that examined nine studies, six studies showed that a dry mouth had a negative effect on speaking, chewing and the retention of removable dentures. In addition, when saliva decreases, thrush and redness under the denture (denture stomatitis) develop more easily. There are few studies directly examining the effect of night-time dryness on teeth fixed on implants; but because the health of the tissue around implants depends on plaque control, cleaning around implants should be an integral part of the evening routine.

The first list describes the picture that suggests causes you can put right at home; the second list describes the picture that calls for seeing a doctor. Examination and, if needed, a sleep test make the definite distinction.

The sequence below moves from the observation you can make at home to the doctor's assessment.

1. 1

   Keep notes for a week

   Every morning, score how severe the dryness is from 0 to 10. Next to it, write down the features of that night: was your nose blocked, did you have alcohol or coffee, did you sleep in your dentures, which medicines did you take in the evening, how many times did you wake up in the night.

2. 2

   Ask the person who sleeps next to you

   Do you sleep with your mouth open, do you snore, does your breathing stop? The NHS writes that sleep apnoea can be hard to notice and that someone watching you while you sleep can help. A few minutes of audio recorded on your phone can also give an idea.

3. 3

   Check your nose during the day

   Can you close your mouth and breathe comfortably through your nose alone for a minute? Close one nostril and try with the other, then the other way round. If one side is constantly blocked, make a note of it.

4. 4

   Review your medicine list

   Check whether a dry mouth is listed in the leaflets of all the medicines you take. Take the list to your doctor; changing the timing of a dose or choosing another medicine may be possible.

5. 5

   GP or ENT

   If there is snoring and pauses in breathing, your GP can refer you for a sleep test; the doctor referring you decides whether the test is done at home or in a sleep laboratory. If a blocked nose is the main issue, an ear, nose and throat specialist assesses it.

6. 6

   A dental check-up

   The dentist assesses the effect of the dryness on the teeth, gums and dentures: new decay, wear at the necks of the teeth, thrush, redness under the denture. Fluoride products and how often you are seen are adjusted accordingly.

There is no single solution for morning dryness; what is done varies with the cause, and often several measures are used together.

The following are the wrong decisions commonly seen with this complaint, and what they cost.

How long it takes to improve depends on the cause. The sequence below is a general framework.

1. When the nose clears

   With temporary blockage, morning dryness often goes once the nose clears.

2. A few weeks with home measures

   The NHS recommends seeing a GP if the mouth is still dry after a few weeks despite home and pharmacy measures.

3. With sleep apnoea treatment

   The NHS writes that CPAP can feel strange at first, but that it works best when used every night. If the dryness persists, the machine settings are reviewed.

4. In the long term

   As long as the dryness persists, the risk of decay and thrush continues. Planning dental check-ups more often helps you get through this period safely.

We do not give a single figure, because morning dryness comes from causes ranging from a simple habit to sleep apnoea. The items that determine it:

Investigating the cause

Whether an ear, nose and throat examination, a sleep test or blood tests are needed.

Sleep apnoea treatment

Options such as a CPAP machine or an oral appliance differ in scope.

The effects inside the mouth

Treating the decay, thrush or denture problems the dryness has caused.