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Thrush — causes and risk factors

Yeast thrives in a warm, moist environment with low acidity and a good supply of sugar. It doesn’t take much to change the pH (acid/alkaline balance) of a healthy vagina to create the ideal breeding ground for candida.

Antibiotics

Many women develop thrush soon after they start a course of antibiotics. There are two possible reasons for this:

1. Antibiotics kill friendly bacteria
   Antibiotic drugs are used to fight a range of common infections. Unfortunately, they can also kill ‘friendly’ bacteria, such as lactobacilli, which help to keep yeast in the vagina under control. Without lactobacilli, the balance in the vagina is disrupted and candida can take over. Although antibiotics have no effect on yeast itself, they can change the environment in the vagina just enough to cause thrush.
   
   
2. Your body may be run down
   If you are taking antibiotics, your body is likely to be run down or weak from an illness. While your body is busy fighting another infection, yeast may seize the opportunity to multiply.

Contraception

1. The contraceptive Pill
   The Pill affects hormones that, amongst other things, can affect a woman’s ability to metabolise (process) sugar. Yeast feeds on sugar, and if there is extra sugar in the body, yeast will use it to grow. The contraceptive pills available now are less disruptive to the body than they used to be. Because of this, it is widely believed that taking the Pill no longer increases a woman’s risk of thrush. Some studies, however, suggest that women who use the Pill may still be more likely to develop thrush, and have recurrent thrush, than woman who do not use the Pill.
   
   
2. Intra-uterine device (IUD)
   Some of the side effects associated with the IUD, such as heavy bleeding and bleeding between periods, also play a role in the development of thrush. (See periods below). Women who use an IUD may also have an increased risk of developing vaginal and uterine infections, which can lead to thrush.
   
   
3. Allergies
   Some women have an allergic reaction to latex condoms, spermicides, or the rubber in diaphragms and cervical caps. Allergy symptoms may be similar to thrush, but the underlying problem is different, as is the treatment. It is essential to get an accurate diagnosis to make sure you are taking the right steps to get better (See diagnosis).

Diabetes

Women with diabetes are more likely to get thrush than are women who do not have diabetes. This is because diabetes increases blood sugar levels, which may, in turn, increase the sugar in vaginal secretions. Diabetic women also tend to have high sugar levels in their urine, and this may contribute to thrush by feeding yeast in the genital area just outside of the vagina.

Diet

Certain foods may have an impact on thrush. Some practitioners believe sugar, dairy products, coffee, tea and wine contribute to thrush by increasing urinary sugar.

Perfumes, deodorants and washing

Anything that changes the natural acidity (pH) of the vagina, or damages the tissues in and around the vagina, may lead to thrush. Perfumed soaps, vaginal deodorants, douches, disinfectants and scented bubble baths can all irritate or damage the delicate tissues of the vagina and vulva. Whether you use perfumed soaps or not, scrubbing, excessive washing or rubbing hard with a towel may do enough damage to lead to thrush.

Periods

Note: Thrush should not affect the foetus as it develops in the womb, but it may be passed on to the baby during vaginal birth. Most babies are exposed to yeast at birth anyway and it generally doesn’t cause a problem. If babies develop thrush, it is usually in their mouths and is easily treated. Ask your GP or midwife for more information. (For treatment of vaginal thrush during pregnancy see treatments.)

Sex

Vaginal thrush is not a sexually transmitted infection (STI) – if you’ve never had sex, you can still get thrush – but sex may play a role in the development of thrush. Penetrative sex can irritate the vagina, particularly when there is little lubrication. Semen may change the acidity of the vagina which can then lead to thrush. And some studies suggest that oral sex increases a woman’s risk of developing thrush. Masturbation has not been linked to thrush.

Thrush can be, but is not always, passed on to a partner during sex. Most women get thrush as a result of their own internal changes or circumstances, not from the person they are having sex with. Men are more likely than women to get thrush through sex.

Your sexual partner does not necessarily need to be treated at the same time as you, but if you continue to get thrush, it may be worth asking your partner to have a check-up.

Tight clothing

Tight trousers, leggings, synthetic knickers or tights prevent air from circulating and can create a warm, moist place for thrush to develop.

Weak immune system

If your body’s immune system is run down due to stress, illness, poor nutrition, HIV, fatigue or serious injury, you may be more vulnerable to thrush. This is because your body is less able to keep the infection at bay.

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Written by Tamara Beus and published in printed format (2001) by Women's Health

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