The fungus Candida is a normal resident of the mouth, digestive tract and vagina that usually causes no harm. Under certain conditions, however, Candida can infect mucous membranes and moist areas of the skin causing 'candidiasis'. Typical areas of infection are the lining of the mouth and vagina, the genital area and anus, the armpits, the skin under the breasts in women, and the skin folds of the stomach. Conditions that enable Candida to infect the skin include hot, humid weather; tight, synthetic underclothing; poor hygiene and inflammatory diseases, such as psoriasis, occurring in the skin folds.
People taking antibiotics may develop candidiasis because the antibiotics kill the 'friendly bacteria' that normally reside on the body, allowing Candida to grow unchecked. Corticosteroids or immunosuppressive therapy after organ transplantation can also lower the body's defences against candidiasis. Inhaled corticosteroids, often used by people with asthma, sometimes produce candidiasis of the mouth. Pregnant women, obese people, and people with diabetes also are more likely to be infected by Candida.
In some people (usually people with a weakened immune system), Candida invades deeper tissues as well as the blood, causing life-threatening systemic candidiasis.
Vaginal thrush is the most prevalent form of candidiasis and is discussed more fully in the following sections:
How common is it?
Vaginal candidiasis prevalence is difficult to gauge as many women self-treat using over the counter (OTC) medication. A Swedish survey of OTC and prescribed anti-fungals for vaginal Candidiasis in the mid-1990s, showed about 85 - 90 cases per 1,000 women in the age group 15 - 45 years.1
As mentioned antibiotic use can encourage vaginal thrush. Post-marketing surveillance of women prescribed quinolone and related antibiotics revealed an incidence of around 600 cases per 100,000 women. The control population (not taking any antibiotics) had about 150 cases per 100,000.2
It is undoubtedly common and estimated to affect about 75% of women in their reproductive years; 10-20% of women have asymptomatic vaginal colonisation with Candida species. Vaginal thrush is most common in 20 - 40 year-olds.
What causes it?
There are a number of factors that have been associated with triggering episodes of thrush. However, with the exception of pregnancy, antibiotics, and poorly controlled diabetes, evidence for individual risk factors has been found to be inconclusive. Accepted risk factors and possible risk factors for thrush are outlined below.
Accepted risk factors:
- Antibiotics
- Pregnancy
- Diabetes mellitus (poorly controlled)
- Immunodeficiency
Possible risk factors:
- Contraceptives
- Sexual behaviour - although thrush is more common during the peak years of sexual activity (during the thirties and forties), there is little evidence to support that the condition is spread during sex, or that there is any benefit in treating sexual partners. However, women who have oral sex may be at greater risk of developing thrush.
- Tight-fitting clothing - wearing tight-fitting clothing, such as tights, or using panty liners, may increase your chances of developing thrush.
What's the outcome?
Treatment for thrush using antifungal medication is ineffective in up to 20% of cases. Treatment for thrush is considered to have failed if the symptoms do not clear up within 7-14 days.
Vaginal thrush can lead to depression and psychosexual problems (anxiety about having sex) can sometimes occur in women who have recurrent thrush.
In rare cases, candidal balanitis (inflammation of the head of the penis) can occur in male partners of women who have thrush.