What Causes Yeast Infections?

The term "yeast" is often used with infections caused by fungi, which:

  • appear in nature as molds, mildews, mushrooms and yeast
  • are more complex than viruses or bacteria
  • number more than 100,000 species, with only 200 causing disease

Candida albicans is the most likely cause. Even though yeast infections happen in millions of people, if you are healthy, they should not be a major health problem.

Superficial Infections

  • involve the skin
  • are not spread easily
  • are caused by Candida that are always in and on the body, but can multiply with a change in pH or hormone balance

Invasive Infections

While yeast infections are mostly harmless, some enter the bloodstream and cause infection inside your body. You are at greater risk if you:

  • have high blood sugar
  • use steroids
  • have had an organ transplant
  • have a weakened immune system
  • have a major illness like AIDS, cancer, liver disease, inflammatory bowel disease or rheumatoid arthritis

Many infections are called secondary or opportunistic because they take hold when your immune system is weak. Fungi can also become invasive in some clinical settings. Long stays in hospitals add to your risk. The fungus may also gather in the urinary tract in patients who use catheters for a long time.

Opportunistic infections can also be from environmental fungi, e.g., aspergilla and Cryptococcus. Some other fungi can be found in soil, animals or trees, and include:

  • Blastomyces: found in the Midwest, on the shores of lakes, rivers and ponds
  • Coccidioides: found in the hot, dry climate of deserts
  • Histoplasma: found in building sites, bird sanctuaries or caves with bats