What causes thrush?

Thrush, also known as candida or candidiasis, is a yeast infection caused by the Candida species of fungus, usually Candida albicans. Thrush is a common vaginal infection in women but men can also get candida infections.

Candida infections can occur in the mouth (oral candidiasis), the top of the penis and, rarely, other parts of the body such as the gastro-intestinal system. Candida skin infection can also occur.

Candida is an organism that is frequently present in the body and does not usually cause any symptoms. The growth of Candida is normally kept under control by the presence of normal bacteria. However, if something alters this balance, an overgrowth of the yeast organism causes a thrush infection. An overgrowth of yeast can occur when the body’s defences are lowered in some way, for example

• Immuno-suppressed patients

Patients with cancer and those receiving chemotherapy.

• Antibiotics

Some antibiotics may cause thrush and many people find that taking certain antibiotics encourages the infection to recur, especially if taken over a long period of time. Antibiotics can kill the bacteria that keep yeast levels down.

• Diabetes

Yeast infections are often associated with diabetes, especially when the blood sugar level is very high. Recurring or stubborn cases of candidiasis may sometimes be an early sign of diabetes.

• Steroid use

Oral thrush can sometimes happen with steroid inhaler use for asthma. Rinsing your mouth with water and spitting out the rinse help to reduce the risk.

• Denture wearers

Oral thrush is more common in people who wear dentures. A dry mouth caused by certain drugs or after chemotherapy or radiotherapy to the head and neck may also lead to thrush. Oral thrush can also be caused by excessive use of antibacterial mouthwash.

• HIV

Very rarely, oral thrush may be one of the early signs of HIV infection. It can become a serious problem if it is left untreated. People with AIDS can also develop thrush elsewhere in their bodies. Drugs that suppress the body’s defence system, such as drugs used to treat AIDS, also cause thrush.

Risk of infection

Candidiasis is not usually spread by sexual intercourse.
Treatment of the sexual partners of women with thrush is not recommended but may be considered in women who have recurrent infection. A minority of male sex partners may have balanitis (inflammation of the penis).

Symptoms

Candida infection can cause swelling and redness of the head of the penis (balanitis) with associated itching or irritation. Yeast infections of the penis are more common when the penis is uncircumcised.

When the mouth is infected (oral candidiasis), the lining of the mouth is often red and sore. Sometimes the yeast causes raised creamy-yellow spots and patches on the tongue and cheek lining. These may leave a raw red area when rubbed (e.g. cleaning teeth). In thrush resulting from antibiotics or steroid use, the affected areas may just appear red and sore.

There may also be red sore areas at the corner of the lips known as angular cheilitis or angular stomatitis. Many mild oral thrush infections are painless, although the condition can sometimes become quite sore.
On the skin, candidiasis produces an itchy red rash.

Diagnosis

Your doctor will ask about your symptoms and examine you. In most cases, thrush can be diagnosed by simply looking at the spots. A sample may need to be scraped off and sent to the laboratory for analysis if oral thrush is suspected. In the case of infection of the penis, a swab may be taken.

Treatment

A variety of antifungal medications are available for oral thrush (drops, lozenges, pastilles and oral tablets/capsules). With treatment, the infection usually clears up in a few days to a week. For penile or skin infections, treatment with topical antifungal agents (creams) relieves symptoms. For severe thrush that has spread to other areas of the body, higher doses and more prolonged treatment may be required.

Preventing oral thrush – oral hygiene

It may be possible to alter one or more of the causes to help prevent further bouts of oral thrush:

It is important to keep your mouth as clean as possible and rinse after meals.

Smoking encourages growth of yeast infections.
Denture hygiene is extremely important for denture wearers who develop oral thrush, as the yeast clings to the fitting surface of the denture. Dentures should be kept out as much as possible, especially overnight. Some yeast infections will resolve completely if the dentures are not worn at night for two weeks.

Dentures should be cleaned in warm soapy water and scrubbed with a soft nailbrush on the fitting surface. The dentures can be soaked in any solution used to sterilise baby’s bottles.

If careful cleaning and hygiene has not helped, you may be prescribed medicated tablets or lozenges. The dentist may want to check your mouth after treatment to check that everything has cleared up.
It is important to have new dentures made every few years.

What else can I do to prevent thrush?

Use antibiotics correctly and avoid inappropriate or prolonged use
Avoid too many antibacterial lozenges
If you have diabetes, good control of your blood sugar level reduces the risk of thrush and other infections.
If you use steroid inhalers, use of a spacer device may reduce the risk of oral thrush. You should also gargle and rinse your mouth after using your inhaler.
If you have dry mouth as a result of taking drugs, take frequent sips of water to keep the mouth moist.
Avoid high sugar diets.
Remember

See your doctor if you are getting recurrent yeast infections or if a yeast infection persists despite treatment.
Discuss with your doctor why you are getting thrush infections and if you need further investigation
Follow the full treatment as prescribed by your doctor.