Oral mycosis: how can it be recognised and treated?

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

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

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

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

• 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 sensation of a sticky mouth often accompany fungal overgrowth.

While “thrush”, corresponding to white patches, is the best-known form, oral fungal infection can also present more discreetly as a simple, intense redness of the tongue or gums. In denture wearers, it may remain asymptomatic for a long time before causing visible inflammation. Whatever its presentation, this infection is a sign of an underlying imbalance that must be identified promptly in order to prevent it from becoming chronic or recurrent.

Oral thrush results from a disruption of the microbiota in the mouth.

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

The most frequent cause in adults lies in the use of certain medications that alter the balance of the microbial flora. Broad-spectrum antibiotics are often singled out: by destroying the beneficial bacteria in the mouth that naturally regulate the fungal population, they leave the field open for Candida to multiply without competition.

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

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

Dry mouth is another important contributing factor. Saliva is not just a simple lubricant: it is rich in antifungal proteins, such as histatin-5, which prevent the fungus from adhering to the mucous membranes. Without sufficient saliva production, the mouth loses its main natural cleaning 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.

Risk is highest at the beginning and at the end of life. Indeed, in the case of the newborn, whose microbiota and immune system are still immature, and in older people, whose defences are declining, oral fungal infections are the most frequent. Certain metabolic diseases, such as diabetes, also promote infection, because high blood glucose increases the level of sugar in saliva, which benefits Candida. Finally, any form of immunodeficiency, such as HIV or nutritional deficiencies, impairs the effectiveness of Th17 lymphocytes, immune cells whose specific role is to monitor the mucous membranes against fungal aggression.

Oral fungal infection can take several forms depending on how the fungus invades and how the host responds. Identifying which type of candidiasis is involved is the first step towards establishing an appropriate treatment.

• Pseudomembranous candidiasis or “thrush” : This is the most common and easily recognisable form. It presents as whitish, creamy plaques scattered over the tongue, palate or inner cheeks. These plaques can be removed by gentle scraping, revealing an underlying mucosa that is red and irritated.

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

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

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

• Denture stomatitis : This form affects denture wearers specifically. It is confined exactly to the area covered by the prosthesis, most often the palate. The mucosa is red and inflamed, sometimes with small granular elevations. It is a direct consequence of poor denture hygiene or wearing the appliance at night.

• Median rhomboid glossitis : This presents as a red, symmetrical, diamond‑shaped area located at the very back of the dorsum 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 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 flora. In most cases, a careful clinical examination by a doctor or dentist is sufficient to establish the diagnosis. However, if the infection does not respond to first-line treatment or if the patient is vulnerable, a mycological sample may be taken. Using a swab, a sort of large cotton bud, the practitioner rubs the lesions to identify precisely the strain of fungus and to check its sensitivity to antifungal agents. This procedure is painless and makes it possible to rule out other diseases of the oral mucosa.

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

For this, topical antifungal agents are generally used as the 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. As an adjunct, antiseptic mouthwashes may be prescribed, but their use should remain 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 your daily habits to prevent it from recurring (frequently cleaning your dentures, systematically rinsing your mouth with water after using a corticosteroid inhaler spray, regularly changing your toothbrush, etc.).

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• 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).