Oral yeast infection: how to recognize and treat it?

Oral mycosis, also called oral candidiasis, is an opportunistic infection caused by the overgrowth of certain fungi. In 95% of cases, the culprit is Candida albicans. This microorganism is naturally present in the mouths of nearly 80% of healthy individuals without causing harm. It lives in balance with the other microorganisms that make up our microbiome. Infection occurs only when this balance is disrupted, allowing the fungus to multiply in an uncontrolled way and invade the superficial tissues.

The symptoms of oral fungal infection can vary depending on the affected area, but certain clinical signs are characteristic of the disease:

• The visual appearance : The most well-known sign is the appearance of white patches or spots resembling curdled milk on the tongue, palate, or inner cheeks.

• Burning sensations : Sharp pain or a burning feeling, especially when consuming acidic, spicy, or hot foods, is common in cases of oral fungal infection.

• Taste alteration : Patients often report a metallic taste in the mouth or a partial loss of taste sensitivity.

• Physical discomfort : Persistent dry mouth, difficulty swallowing, or a sticky, pasty sensation in the mouth often accompany fungal overgrowth.

While “thrush,” corresponding to white patches, is the best‑known form, oral fungal infection can also present more subtly as a simple, intense redness of the tongue or gums. In people who wear dental prostheses, it can remain asymptomatic for a long time before causing visible inflammation. Whatever its presentation, this infection indicates an underlying imbalance that should be identified promptly to prevent it from becoming chronic or recurrent.

Oral fungal infection results from an alteration of the mouth’s microbiota.

This is called an opportunistic infection because the fungus becomes aggressive only when it detects a weakness in its host’s defenses. This shift can be triggered by external factors or by internal changes within our body.

The most common cause in adults lies in the use of certain medications that alter the balance of the microbiota. Broad-spectrum antibiotics are often implicated: by destroying the beneficial bacteria in the mouth that naturally regulate the fungal population, they give Candida free rein to multiply without competition.

Similarly, inhaled corticosteroids, which are essential for people with asthma, can locally weaken the immune defenses of the mucous membranes if they are not followed by systematic mouth rinsing. In more intensive clinical contexts, such as chemotherapy or radiotherapy, the direct damage to tissues and salivary glands creates a major breach that yeasts can easily exploit.

Certain local factors also promote fungal infection of the tongue. The wearing of dental prostheses is a major risk factor, especially if the appliance is poorly fitted or worn at night. Under the acrylic plate of the denture, an area of maceration that is low in oxygen and acidic forms, which is ideal for fungal growth.

Dry mouth is another major contributing factor. Saliva is not just a simple lubricant: it is rich in antifungal proteins, such as histatin-5, which prevent the fungus from attaching to the mucous membranes. Without sufficient saliva production, the mouth loses its primary natural cleansing system. Finally, smoking irritates the tissues and alters the oral pH, thereby promoting the transformation of the fungus into its invasive form.

Immunity is the final barrier against candidiasis.

The risk is highest at the beginning and at the end of life. In fact, in the newborn, whose microbiota and immune system are still immature, and in the elderly person, whose defenses are declining, oral fungal infections are the most common. Certain metabolic diseases, such as diabetes, also promote infection, because high blood glucose levels increase the sugar content of saliva, which is beneficial for Candida. Finally, any form of immunosuppression, such as HIV infection or nutritional deficiencies, impairs the effectiveness of Th17 lymphocytes, immune cells whose role is precisely to monitor mucous membranes against fungal attacks.

Oral mycosis can take several forms depending on how the fungus invades and how the host’s body responds. Identifying which type of candidiasis is involved is the first step toward implementing an appropriate treatment.

• Pseudomembranous candidiasis, or “thrush” : This is the most classic and most easily recognizable form. It appears as whitish, creamy patches scattered over the tongue, the palate, or the inside of the cheeks. These patches can be removed by gentle scraping, revealing a red, irritated mucosal surface underneath.

• Erythematous or atrophic candidiasis : Less conspicuous but often more painful, it does not present with white patches. The mucosa becomes bright red and very sensitive. It often affects the dorsum of the tongue, which loses its papillae and becomes completely smooth. This is the form frequently observed after taking antibiotics or in patients living with HIV.

• Angular cheilitis or perlèche : This form occurs outside the oral cavity, specifically at the corners of the mouth. It causes redness, painful cracks, and sometimes yellowish crusts. It is often promoted by stagnant moisture in the folds of the lips, particularly in older adults whose skin is sagging or in children who frequently lick their lips.

• Chronic hyperplastic candidiasis : This is a rarer and more persistent form. It appears as firm, adherent white patches, often located on the inside of the cheeks. Unlike thrush, these patches cannot be removed by scraping. It mainly affects people who smoke and requires close monitoring because there is a risk of malignant transformation if it is not treated.

• Denture stomatitis : This form specifically affects people who wear dentures. It is strictly limited to the area covered by the prosthesis, most often the palate. The mucosa appears red and inflamed, sometimes with small, granular-looking elevations. It is the direct consequence of poor denture hygiene or wearing the appliance at night.

• Median rhomboid glossitis : It appears as a red, symmetrical, diamond-shaped area located at the very back of the dorsal surface of the tongue. Long regarded as a congenital malformation, it is now known to be a chronic infection caused by Candida, often associated with smoking or the repeated use of corticosteroids.

Although the visual appearance of candidiasis is often characteristic, medical management is necessary to confirm the diagnosis and, above all, to identify the underlying cause of the imbalance in the microbiota. In most cases, a careful clinical examination by a physician or dentist is sufficient to establish the diagnosis. However, if the infection is resistant to first-line treatment or if the patient is vulnerable, a mycological sample may be taken. Using a swab, similar to a large cotton swab, the clinician rubs the lesions to precisely identify the fungal strain and assess its sensitivity to antifungal agents. This procedure is painless and helps rule out other diseases of the oral mucosa.

The goal of treatment is twofold: to eliminate the excess fungi and restore a healthy oral environment.

To achieve this, topical antifungal agents are generally used as first-line treatment. They are available as syrups, gels, or lozenges and often contain nystatin or miconazole. Before swallowing, to ensure effectiveness, it is important to keep the product in contact with the mucous membranes for as long as possible. Additionally, antiseptic mouthwashes may be prescribed, but their use should be limited in duration so as not to further disrupt the protective bacterial flora.

Note : Depending on the cause of the fungal infection, it may be necessary to review daily habits to prevent recurrence (frequently cleaning dental prostheses, always rinsing the mouth with water after using a corticosteroid inhaler spray, regularly changing one’s toothbrush, etc.).

• GUEDJ A. & al. Mycoses buccales. EMC - Stomatologie (2005).

• JABRA-RIZK M. A. & al. Oral candidiasis: A disease of opportunity. Journal of Fungi (2020).

• TEE TAY S. & al. Candida species and oral mycobiota of patients clinically diagnosed with oral thrush. Plos One (2023).

• RAJA A. & al. Oral candidiasis. StatPearls (2023).