Oral thrush in adults - Causes 

Causes of oral thrush in adults 

Oral thrush infections are caused by increased levels of Candida albicans fungi, which are naturally present in the mouth.

This increase may result from:

  • using an inhaler to take corticosteroid medication  
  • certain medications which reduce the amount of saliva produced
  • an injury in the mouth
  • smoking 
  • the immune system being weakened (immunodeficiency)
  • an underlying health condition, such as cancer or HIV

Corticosteroids can be used to reduce inflammation (swelling) and treat a variety of conditions such as:

  • some types of cancer
  • arthritis, a condition that causes inflammation of the bones and joints 
  • eczema,  a long-term skin condition that causes itchy, dry and red cracked skin
  • asthma,  a long-term condition that causes the airways of the lungs to become inflamed and swollen
  • COPD, (chronic obstructive pulmonary disease) a collective name for lung diseases (including chronic bronchitis, emphysema and chronic obstructive airways disease) that cause breathing difficulties

Inhaled corticosteroids are often used to treat asthma. The medicine is delivered through an inhaler, or spacer, (a plastic cylinder attached to your inhaler which increases the amount of medication reaching the lungs and minimising contact with your mouth). Inhaled corticosteroids cause fewer side effects than other forms of treatment but can change acidity levels in the mouth. The change kills healthy bacteria and causes an imbalance that makes oral thrush more likely to develop.

Risk factors

You are at an increased risk of developing oral thrush if:

  • you have diabetes
  • you are a certain age (oral thrush is more common in infants and elderly people) 
  • you have high blood sugar levels
  • you wear dentures that are poorly fitted or not cleaned regularly
  • you often take antibiotics (medication used to fight infections)
  • you have an iron deficiency or B-vitamin deficiency
  • you are having treatment for cancer such as chemotherapy or radiotherapy

Page last reviewed: 01/08/2012

Next review due: 01/08/2014


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