The diagnosis of oral candidiasis is usually based on its clinical appearance with the distinctive white lesions on the mouth, tongue, or cheeks, during a visual examination of the mouth. If in doubt, your doctor or dentist may refer you to an Oral Pathologist to get a microscopic histological examination or a culture of intraoral scrapings to identify the Candida species and rule out other illnesses in order to confirm the diagnosis.
In severe cases, when it is suspected that the infection has spread beyond the throat, an endoscopic examination may be required to check for the extend of the infection.
If a patient has frequent or persistent outbreaks of oral thrush symptoms, the doctor or dentist may recommend additional diagnostic tests to check for undiagnosed medical illness, such as diabetes, cancer or HIV infection. A biopsy of affected tissue may be indicated, especially when candidiasis is suspected in conjunction with some concurrent pathology, such as epithelial dysplasia, squamous cell carcinoma, or lichen planus.

Oral Thrush is caused by the growth of Candida albicans. Although Candida albicans is a type of fungus naturally found in most of the healthy mouths, its overgrowth can cause an outbreak of oral thrush symptoms. The Candida albicans population in the mouth is kept under control as it is competing with the other bacteria and micro-organisms of the mouth.
Any condition that changes the natural balance of the microbial ecosystem of the mouth can potentially be the reason for an oral thrush infection.
The causes of oral thrush are conditions that either affect the immune system or alter the oral mucosal environment.
Immune system related causes of oral thrush :
A weakened immune system increases the chances of developing thrush, because of reduced ability of the body to control viruses, bacteria, or fungi and to stop infections. That is why oral thrush symptoms are common in elderly people and babies, as they have in general a weaker immune system and they are more susceptible to infections.
Population groups with a weakened immune system include :
- persons with poor general health,
- cancer patients receiving radiation therapy/chemotherapy
- people infected with HIV/AIDS
- having Hypothyroidism or Hyperparathyroidism
- taking drugs to suppress the immune system following an organ transplant
Thrush can be very serious for patients with cancer or HIV as it further weakens the immune system and, if allowed to spread into the throat, affects their nutrition and causes respiratory problems.
Oral mucosa environment related causes of oral thrush :
Taking antibiotics or steroids may alter the oral mucosal environment by suppressing certain species of mouth bacteria in favor of others, one of which might be Candida albicans, leading to oral thrush.
Another common cause of oral thrush symptoms is xerostomia or dry mouth syndrome. People with dry mouth have less saliva which disrupts the chemistry of the mouth and may help in developing an oral candidiasis infection.
Poor oral hygiene, heavy smoking, excessive alcohol consumption, stress and certain medications that change the chemical balance of the mouth may have the same effect.( causing the fungus Candida to grow out of control, causing infection)
Patients with diabetes have saliva that contains large amounts of sugar, which encourages the growth of Candida..
Wearing dentures that are not properly maintained or fitted can be responsible for some type of oral thrush.
A newborn may acquire the Candida fungus during delivery, if the mother had an active vaginal candidiasis. Symptoms of oral thrush usually follow within 7 to 10 days after birth.