Candida is a family of fungi that live on the human skin and around the vagina without causing any problems or symptoms. They are harmless and the majority of the time the immune system and bacteria that live on the skin prevent candida from multiplying, but if conditions change fungi numbers can rapidly increase causing infection. Candida thrives in warm, moist and airless conditions which is why the vagina is susceptible to infection.

There are a number of factors which are recognised as triggers of vaginal thrush:

Antibiotics - thrush occurs in approximately 30%¹ of women who already have the candida fungus present in the vagina and are using oral or intra-vaginal antibiotics. Antibiotics are known to change the environment in the vagina as they remove the bacteria that naturally prevent the candida from multiplying.

Pregnancy - changes in the levels of hormones, e.g. oestrogen during pregnancy can increase the chances of developing thrush. The recurrence of symptoms and reduction in relief of symptoms from treatments is more common during pregnancy. Pregnant women are also more likely to have asymptomatic thrush.

Diabetes - women who have poorly controlled diabetes are more likely to develop symptoms of thrush than those who control their condition. Recurrent episodes of thrush can be one of the first signs of undiagnosed diabetes and is one of the reasons why more than two episodes in six months is a referral criteria.

Weakened immune system - the risk of developing thrush is higher in women who have reduced immune function, e.g. HIV, AIDS or are using medication that impairs immune function such as chemotherapy, steroid therapy or some anti-arthritic drugs. The reduced immune function means that the body's immune system is unable to control the levels of candida.

There are a number of other factors associated with the causes of thrush but as yet there is little clinical evidence to support them as being triggers:

Contraceptive pill - there are possible links between the oral contraceptive, particularly the combined form, and the development of thrush.

Sexual behaviour - there is only weak evidence to demonstrate a link between increased sexual activity and the risk of developing thrush. It is not a sexually transmitted disease and there are no recommendations to treat a male partner if a woman has thrush except to prevent reinfection or if the partner is showing symptoms.

Female hygiene - the use of fragranced soaps, gels or vaginal douching doesn't increase the risk of developing thrush. There is also no evidence that sanitary products, such as towels and tampons are associated with the condition when they are used appropriately.

Tight fitting clothing - there is no link between wearing tight clothing or non-cotton underwear and the condition.