What causes thrush? Is recurrence related to bad habits?

It is not yet possible to state the real cause of the cold sore or why it appears more frequently in some people. In general, it is indicated that there are multifactorial causes that favor the appearance of lesions in the mouth, such as autoimmune changes, injuries, predisposition, gastric changes or emotional conditions.

When they appear in an isolated and punctual manner, there is no great need to investigate the causes of cold sores, but if they are recurrent or lasting, help should be sought for the problem that may be related to the habits or changes in the body.

Know some of the probable causes of thrush:


Traumas or injuries

Hitting your gums with a toothbrush, flossing incorrectly or biting your cheek can be one of the triggering factors of cold sore.

People who use orthodontic braces, prostheses or dentures and usually have lesions on the cheek or gums may have a higher incidence of cold sore.

Strong or hard foods

Foods that are too hard or difficult to chew, such as peanuts or popcorn, can damage the gums and favor the thinning of epithelial tissue, or even the popcorn shells can cause microlesions in the mucosa.

Spicy or very strong foods, on the other hand, can irritate the epithelial tissue, weakening it. If it is something more acidic, like vinegar, the pH of the mouth can be affected and cause injuries due to acid imbalance in the region.

Oral care products

Maintaining the correct cleaning and hygiene of the mouth is essential, including being able to reduce the risks of cold sore or improve recovery.

But sometimes, the chosen products can be the source of the ulcers. In general, alcohol mouthwashes tend to be irritating to the mucosa and cause burning and fragility of the epithelial tissue.

Among the components that cause the most oral irritations is sodium lauryl sulfate (Sodium Lauryl Sulfate), which acts as a very cheap disinfectant (therefore, advantageous for the industry). Its function is to help clean teeth and mouth, but in return there are several risks associated with it.

In hygiene products, the amount of sodium lauryl sulfate is very low and controlled, being considered safe by health regulatory agencies. Even so, cases of irritation,  allergy  and degradation of the skin and mucous tissues are strongly associated with its use.

Read more: What is oral health? Know your importance and care tips

Dropped immunity

Any condition that causes a fall in the body’s defense system can be the triggering factor for a cold sore.

In this group, a series of conditions can be encompassed, such as diseases that weaken the organism, use of medications such as corticosteroids, chronic diseases, stress and poor diet.


It is possible that people with infectious agents (viruses and bacteria, for example) are more susceptible to developing thrush. In this case, the condition is still likely to be multifactorial, also due to reduced immunity.

However, Streptococcus-  type bacteria  (which causes  sinusitis , for example) and cytomegalovirus-type viruses (which causes  chickenpox  and herpes, for example), Epstein-Barr (which causes mononucleosis) and varicella zoster (which causes chickenpox) are more associated. to thrush.

Read more: Cold sores: symptoms, treatment, medicine, ointment, how to cure?


It is not known exactly which mechanism relates stress to thrush. However, it is possible for predisposed people to suffer from mouth ulcers when they experience stressful situations or are emotionally shaken.

Bad eating habits

You may not be eating any food that is too hard or too bad to chew, but if your meals are nutritionally poor, this could be the reason for thrush.

Read more: What is the Food Pyramid? Types (Brazilian), benefits and groups

The deficiencies of folic acid , iron, selenium, zinc and vitamins of the B complex are the most related to mouth ulcers.

Again, thrush is usually multifactorial and the causes add up. Therefore, when you eat poorly, the body lacks nutrients that can favor the appearance of a small ulcer.

However, along with this, immunity also low, the organism is weakened and the chances of the injury appear are greater.


Among the possible causes of the incidence of thrush is genetic inheritance. Thus, in addition to food and routine care, it is possible that there are people more predisposed to suffer from mouth sores, either in frequency or in intensity.

That is, constant injuries with no apparent cause or injuries that almost never manifest themselves, but when they occur they are intense, large or long-lasting.

Gastric changes

Punctual or prolonged changes in the pH (acidity) of the stomach can facilitate the appearance of thrush.

Among the causes of the occasional changes are very acidic food and the use of non-continuous medications. Among the prolonged dysfunctions, there may be reflux,  gastritis , the use of continuous medications or the overuse of antacids.

In the case of refluxes, the acidity of the gastric juice returns to the mouth and affects the mucous membranes. As the region is sensitive, even small amounts of gastric acid can cause severe irritation and result in constant thrush.

Allergic reactions

Called allergic thrush, mouth ulcers can result from exaggerated immune responses, that is, allergies.

They can occur when the person already has some known sensitivity (be it to foods or chemicals) or when allergies occur with no known cause.

This type of cold sore is quite common in patients with food intolerance or sensitivity, for example gluten , milk, chestnuts and shrimp, who can manifest different reactions when coming into contact with food.

Read more: What is lactose intolerance, symptoms, medicines, tests, is it curable?


Any medication that causes allergic reactions can have, among the adverse effects, the development of thrush. However, the most common are anti-inflammatories, methotrexate ,  aspirin  and  atenolol .

Medicines that interfere with stomach pH can cause cold sore, as they alter the acidity of the stomach (including antacids used continuously). In addition, drugs that affect immunity, such as corticosteroids, can also have an indirect impact, increasing the risks of ulcers.

It is necessary to inform your doctor when symptoms or adverse reactions arise with the use of medications. Also, never interrupt treatment. Talk to the professional so that the best options are evaluated.