Most of the time we live in harmony with Candida, a strain of yeast that calls the human body home. We don't even know it is there. But give yeast the right conditions—a moist environment and a weakened immune system—and it will grow and flourish.

Then we have a problem.

And it is not just a woman's problem. In addition to vaginal yeast infections, overgrown yeast causes diaper rash in infant girls and boys, oral thrush, breast infections in nursing mothers, jock itch and serious bloodstream infections.

Meet yeast

Candida is related to, but different than bakers or brewers yeast (Saccharomyces) used in food and beer. It is a single cell organism found mainly in our digestive tract, skin and other body cavities like the mouth, genitals and the ears—places on the body that are warm and moist. Like all yeast, Candida also is a fungus.

“Candida is quite a unique organism,” says Mike Lorenz, PhD, assistant professor of microbiology and molecular genetics at the University of Texas Medical School at Houston. Our bodies have an awful lot of microorganisms in them, but very few of those are fungi. Candida is not found in the environment we don't pick it up from eating contaminated food or from water or from breathing it in. The only place it is known to live is in warm-blooded animals like us.”

The cell structure of Candida is nearly identical to that of a human cell, which is why scientists frequently use its cousin, baker's yeast, as a model organism in their research.

Strength in numbers

What causes yeast to grow out of control? Contrary to popular theories and diets, eating too much sugar is not to blame, but rather changes in the body's internal environment. Normally, good bacteria and other organisms in the body keep yeast growth in check. When the good guys are gone, yeast sees an opportunity to grow and takes it. A weakened immune system also allows yeast to grow.

“When you take antibiotics, you kill off a lot of the friendly microbes living in your body, and allow the other ones that are not killed by the antibiotics to overgrow,” Lorenz says. “As a result, many women will develop vaginal yeast infections after using antibiotics.”

He adds an estimated 75 percent of women in the United States will have a yeast infection once in their lives. A small subset of American women develops chronic yeast infections. For them, yeast infections are quite debilitating and may require the help of a specialist.

Most yeast infections are caused by an overgrowth of an individual's own yeast, but yeast infections also may be transmitted through sexual contact. That means men can have them too. Newborn babies also may catch a yeast infection from their mothers during birth. Breastfeeding mothers can get yeast infections from babies with oral thrush.

Oral thrush is a yeast infection in the mouth, a condition most common in babies under six months whose immune systems are less developed. Oral thrush also is common in persons with HIV/AIDS, and is one of the leading AIDS defining illness, since oral thrush is rare in adults with healthy immune systems.

The most serious of yeast infections occur in the bloodstream and can be deadly. Bloodstream yeast infections typically occur in persons who are hospitalized and have weak immune systems, for example, organ recipients, patients who have had major surgery and patients with HIV or cancer. In very rare cases, patients may contract a bloodstream yeast infection from medical equipment or devices contaminated with yeast. Candida infections are the fourth most common bloodstream infection among hospitalized patients in the United States according to the Centers for Disease Control.

“The number of Candida infections has been going up steadily over the past 25 to 30 years to where it has become a serious issue,” Lorenz says.

He attributes the increase to patients living longer because of advances in treating cancer, organ failure and other medical conditions.

“Those people we are keeping alive in a very weakened state are susceptible to infections that people didn't used to get,” Lorenz says.

Yeast and desist

The symptoms of a yeast infection are unpleasant, no matter where it is on the body. An itching and burning sensation is common with skin infections and vaginal infections. Women with vaginal yeast infections may also have a cottage cheese-like discharge. Oral thrush shows up as white patches on the lips and the tongue, making swallowing difficult and painful. Babies with a yeast-caused diaper rash have a red, bumpy and itchy rash on their groin, thighs and abdomen.

“Most of the time, the diagnosis can be made clinically by the appearance of the yeast overgrowth,” says Luis Ostrosky-Zeichner, MD, associate professor of medicine in the Division of Infectious Diseases at UT Medical School and an editor of doctorfungus.com, an online reference guide to fungal infections. “What we usually see are whitish flecks that slough off. Doctors can do microbiological testing and examine samples with the microscopes to make sure.” Ostrosky-Zeichner also is medical director for epidemiology at Memorial Hermann Hospital - Texas Medical Center.

Bloodstream infections are harder to diagnose because patients may not have any specific symptoms. Fever and chills after receiving antibiotic therapy are the most common symptoms. If the infection spreads to the body’s organs, the symptoms will vary based on the source of the infection. Blood tests are the only way to accurately diagnose bloodstream yeast infections.

Treatment

Mild cases of yeast infections can be treated with good hygiene or the conditions of the body, such as wearing less constrictive clothing to promote airflow. For athlete’s foot, keep feet dry. Topical and oral antifungal medications may also help knock out the infection. However, proper diagnosis of yeast infections is important. Studies have shown that as many as two-thirds of all over the counter drugs sold to treat yeast infections were used by women without the disease.

“Since we started to introduce all these topical antifungals, or patients they take them too long, we have started to see some yeast that are resistant to antifungals,” Ostrosky says.

Bloodstream infections are much harder to treat. Studies show that an estimated 40 percent of patients with bloodstream infections die, a mortality higher than any common bacterial infection.

“There are only a couple of antifungals to use against bloodstream yeast infections and these antifungals all have serious drawbacks,” Lorenz says. “Some of them are poorly tolerated by patients, so they can't be given for long periods of time. Others simply are just not that effective. Because very few people got bloodstream infections from Candida 30 or 40 years ago, there wasn't a lot of development of antifungal drugs to treat them.

“The problem with developing antifungal drugs is that the cell biology of fungi is virtually identical to the cell biology of humans,” he continues. “So finding drugs that are effective against fungus, but benign toward the patient is very difficult to do.”

Lorenz is studying the biology of Candida and the role immunity plays in stemming yeast overgrowth. His lab currently is conducting pilot studies on potential new antifungal medications.

Don't believe the hype

Google “yeast” and the list of ailments caused by this usually benign microbe go on and on. Both Drs. Ostrosky and Lorenz urge caution when relying on Internet information about yeast, especially those sites or companies offering yeast-cleansing treatments.

“The theory is that you have a yeast overgrowth in your intestinal track and that is somehow associated with everything that could be wrong with your body, such as fatigue, obesity, bloatedness and digestive issues, depression,” Ostrosky says. “There is no evidence that this occurs. Be skeptical.”

 

 

Last Updated: 12-03-2008

Editorial Board | Legal Disclaimer | Privacy & Security | Contact Us

©2000-2009 Office of Institutional Advancement, UT-Houston