The sense of taste can detect four primary tastes – sour, sweet, bitter and salty. A fifth taste sensation known as unami can be associated with savory tastes. Most of the time, the taste sensations are triggered by different foods and drinks, however, in some cases a taste may be detectable despite not eating or drinking. A taste disorder is broadly known as dysgeusia and a bad taste in the mouth without appropriate stimuli is known as cacogeusia.
A sour taste is triggered by the presence of acids in the foods or drinks that are consumed. The relative taste index for various foods and drinks differ, with the strongest stimulation caused by acids like formic, hydrochloric and chloracetic acid. The acids with the lowest indices include acetic and citric acid. This means that a food or drink containing formic acid or hydrochloric acid will trigger more pronounced sour taste sensations.
What causes a sour taste in the mouth?
Consuming a food or drink that is acidic will trigger the sour taste sensation. Citrus, vinegar, fermented foods and drinks and some offal meats are more likely to taste sour. This also depends on the preparation of the food or drink and other additives that may alter the taste. A sour taste, like any taste sensation rapidly diminishes as saliva washes away the trigger chemicals in foods and drinks and the nerves adapt to the stimulus. However in a person with any cause of mouth dryness, the taste sensation may persist for long periods afterwards.
However, a sour taste in the mouth is often associated with the stomach contents, which are usually acidic due to the presence of hydrochloric acid. Usually the stomach contents are isolated to the stomach and then pass into the duodenum, the first part of the small intestine, for the process of digestion to continue. Stomach acid is an important part of the digestion process, breaking down foods into smaller compounds and activating other enzymes in the stomach and duodenum to continue with digestion.
In acid reflux, the stomach contents rise up the esophagus and can reach the throat or mouth cavity. Most cases of acid reflux will result in a burning chest pain, known as heartburn. At times, heartburn and many of the other common signs and symptoms associated with acid reflux may be absent except for a sour taste in the mouth. Acute episodes of acid reflux may occur after overeating, consuming excess amounts of alcohol, sleeping immediately after a large meal or exercising after eating. This is further discussed under sour stomach. In patients without acid reflux, it may be a result of vomiting.
Chronic cases of acid reflux, known as GERD (gastroesophageal reflux disease), causes the backward flow of stomach acid at any time in the day or night. While acute exacerbations may occur with the same factors mentioned above, GERD is due to a dysfunctional lower esophageal sphincter (LES). Usually the LES prevents the backward flow of stomach contents by remaining contracted except to allow food and drink from the esophagus to enter into the stomach. In GERD, this protective mechanism fails and varying amounts of stomach acid can enter the esophagus at any time.
Another common causes of a sour taste is the presence of pus. This is seen with infections, primarily those affecting the mouth, nasal cavity, throat, upper esophagus and airways. Immune cells contain lysosymes, which are enzymes that can digest invading microorganisms, are abundant in pus. Coupled with enzymes released from the damaged microorganism, toxins produced by these pathogens and necrotic cells in the pus, it can cause a strong sour taste in the mouth.
Sour Taste in the Mouth in the Morning
Awaking with a prominent sour taste in the mouth is commonly seen with GERD. The acid reflux is often exacerbated at night due to increased gastric acid secretion, relaxation of the LES and lying flat. This is further aggravated by eating a large meal or drinking alcohol before sleeping.
Acid reflux may also present with heartburn, morning sore throat, water brash (excessive saliva in the mouth), nausea, regurgitation and indigestion. Patients may also report a prominent bad morning breath. Refer to acid reflux causes and chronic reflux for more information on acute and chronic reflux respectively. The condition may improve slightly by elevating the head of the bed.
Nasal infections, acute sinusitis and infections of the airways may also be responsible for a sour taste in the mouth in the morning, especially if the pus accumulates in the mouth and throat during sleep.
Sour Taste in the Mouth During Pregnancy
Increased abdominal pressure associated with pregnancy may affect the functioning of the LES. This allows for the stomach contents to spill over into the stomach and is the reason why acid reflux is so common in pregnant women. Obese women are at a greater risk, as well as those carrying multiple fetuses, especially is there is a prior history of GERD. Vomiting associated with morning sickness may also cause a sour taste in the mouth. during pregnancy This is relieved with proper oral hygiene.
Pregnant women may find that the acid reflux symptoms resolve after pregnancy. Simple measures like eating smaller meals more frequently, not sleeping or lying down after eating and lying on the side (preferably left side) may help reduce the extent of the reflux during pregnancy.
Sour Taste in Mouth After Eating
Acid reflux is more prominent after eating especially in a person with gastroesophageal reflux disease (GERD). Certain foods and drinks are more likely to cause reflux leading to a sour taste in the mouth. This includes alcohol, chocolates, spicy foods and patients may report a sensitivity to individual foods. This is discussed further under acid reflux diet.
Avoiding these foods and drinks, eating smaller meals and avoiding strenuous exercise and sleeping immediately affter eating may help to avoid the acid reflux symptoms.
Sour Taste in Mouth After Coughing
Coughing may help to expel sputum containing pus from the airways and throat. This is more likely to be seen with bronchitis, tracheitis and laryngitis, as well suppurative tonsillitis and even nasal cavity infections. Sneezing may also cause a similar effect, especially with nasal infections. The sudden and forceful expiration helps to expel the mucus trapped lower down in the airways.
Patients with GERD may also experience a sour taste in the mouth after coughing. The raised pressure associated with coughing and sneezing may propel stomach contents up into the esophagus and even as high as the throat and mouth following a cough or sneeze. This is more frequently seen with a persistent cough. Treating the cause of the cough is important to avoid further recurrences.