Our tongue enables us to distinguish between four different primary tastes: sweet, sour, salty, and bitter. There is also a fifth taste referred to as umami, which we can identify as a meaty or savory taste sensation. Our ability to distinguish between these different taste sensations is dependent on the different types of chemical receptors located in different regions of the tongue.
The taste sensations are triggered when chemicals in our food and beverages interact with the different types of receptors present on the tongue. Not all taste sensations are triggered by the physical presence of food on the tongue. Sometimes, taste sensations may arise even in the absence of any food or drink. Such abnormal taste sensations are also referred to as dysgeusia. Cacogeusia refers to a condition in which a bad taste is present in the mouth even in the absence of any food or drink.
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Why is there a sour tase?
The sour taste sensation is caused by the interaction of acids in our food with the appropriate chemical receptors on the tongue. Not all acids are perceived to be sour to the same extent. This is because acids differ in their ability to stimulate the sour taste receptors present on the tongue.
Acids like citric acid and acetic acid trigger relatively weaker sour taste sensations than hydrochloric acid and formic acid. A relative taste index for various foods and beverages can be constructed based on the differential abilities of various acid components in triggering sour taste sensations.
Causes of Sour Taste in the Mouth
Acid in food and beverages
As mentioned previously, the sour taste sensations are normally triggered by the interaction of various acids present in foods and beverages with the appropriate chemical receptors on our tongue. Examples of foods that commonly elicit sour taste sensations include citrus fruits, fermented foods and drinks, vinegar, and some kinds of offal meats. Additives added during food preparation can also make the food taste sour.
As with any other taste sensation, the sour taste diminishes rapidly as the triggering chemicals get washed off from the tongue by the saliva. In case of people who suffer from dry mouth, the sour taste sensations persist for a relatively longer period. Sour taste sensations also diminish in the continuous presence of the triggering chemicals as the sensory nerves quickly adapt to the stimulus.
Reflux of gastric acid
The hydrochloric acid that is produced in the stomach plays an essential role in the digestive processes. The acidic contents of the stomach are normally separated from the esophagus by the lower esophageal sphincter. The peristaltic movements of the gut move the stomach contents down into the duodenum, which constitutes the first part of the small intestine.
Sometimes, the contents of the stomach may enter the esophagus and reach the throat and the oral cavity. This acid reflux causes a strong sour taste in the mouth, along with a burning pain sensation in the chest (also known as heartburn).
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In some cases, a sour taste in the mouth may be the only symptom associated with acid reflux. Acid reflux into the oral cavity can be caused by a variety of conditions, including vomiting, excessive alcohol consumption, excessive physical activity after eating, and lying down immediately after a big meal. These acute cases of acid reflux usually resolve on their own.
Pus can also elicit a sour taste in the mouth. This is especially the case when infections occur in the mouth, throat, nasal cavity, esophagus and the upper airways. Pus contains the enzyme lysozyme (released by the immune cells to destroy the invading bacteria), enzymes and toxins secreted by pathogens, and dead cells. Together, all these substances can elicit a strong sour taste in the mouth.
Sour taste in the mouth in the morning
Some individuals may have a sour taste in the mouth when they get up in the morning. This is a common occurrence in patients suffering from gastroesophageal reflux disease. Sleeping increases the chance of acid reflux due to the supine sleeping position, relaxation of the lower esophageal sphincter, and increased acid secretion during the night hours. Consuming alcohol or having a large meal just before sleeping aggravates the condition.
Along with the sour taste in the mouth, the affected individuals may also experience morning sore throat, nausea, excessive salivation, indigestion, regurgitation and heartburn. Bad breath in the morning may also be evident. Elevation of head while sleeping may help people who suffer from gastroesophageal reflux disease. Apart from gastroesophageal reflux disease, acute sinusitis, nasal infections, and airway infections can also cause sour taste in the morning. This is especially the case when pus from these infections accumulates in the throat and the mouth during sleep.
Sour taste in the mouth during pregnancy
Pregnant women are especially prone to suffering from acid reflux. This is because the increased abdominal pressure in these women may prevent proper closure of the lower esophageal sphincter. Women carrying multiple fetuses and obese women are at an increased risk of having acid reflux. In addition, the vomiting caused by morning sickness in pregnant women can also leave a sour taste in the mouth.
Maintaining proper oral hygiene may help in relieving the sour taste. Other measures to combat the problem include eating frequent small meals throughout the day rather than a few large meals, avoiding lying down immediately after eating, and lying on the sides (rather than on the back) while sleeping.
Sour taste in the mouth after eating
People suffering from gastroesophageal reflux disease are more likely to have acid reflux after a meal. Also, acid reflux is more likely after consuming certain foods such as spicy meals, chocolates, and alcohol. Individuals may be particularly sensitive to certain foods, which should be avoided in order to decrease the risk of acid reflux.
Sour taste in the mouth after coughing
Sneezing and coughing may also leave a sour taste in the mouth. Coughing helps in the expulsion of sputum, which may contain pus. This is especially the case in conditions such as laryngitis, tracheitis, bronchitis, suppurative tonsillitis, and nasal cavity infections. Also, patients suffering from gastroesophageal reflux disease have a higher chance of experiencing sour taste in the mouth after a cough. This is because the pressure developed during coughing and sneezing can push the stomach contents upwards.