Tinea versicolor is caused by an overgrowth of Pityrosporum orbiculare. Also known as Malassezia furfur, Pityrosporum ovale or Malassezia ovalis, Pityrosporum orbiculare is a type of yeast which is normally present in small amounts on the surface of the skin.

Under normal circumstances, the yeast lives in the pores but remains on the skin’s surface. Under certain conditions (such as high heat and humidity), the yeast changes from its usual round or oval form to a string-like, branching shape. When the yeast changes shapes, it is called hyphae. In this form, the yeast migrates under the skin and produces azelaic acid, a substance that can change the amount of pigment (color) in new skin cells. It is not known why some people develop tinea versicolor and others do not.

In tropical climates where the temperature and humidity are high year-round, tinea versicolor may occur throughout the year. In areas with cooler temperatures, the condition generally occurs during the warm months of the year.

Other factors that have been associated with an increased risk of developing tinea versicolor include:

• Age. The condition is more common among adolescents and young adults when the sebaceous glands (glands in the skin that secrete oil to the skin’s surface) are more active.
  
  
• Heredity. The condition tends to run in families.
  
  
• Oily skin. The yeast that causes tinea versicolor requires oil to grow, so people with oily skin are more likely to develop the condition.
  
  
• Use of bath oils and skin lubricants. Because the yeast that causes tinea versicolor is lipophilic (attracted to fat), use of these products may increase the risk of developing the condition.
  
  
• Excessive sweating (hyperhidrosis). May cause excess growth of the yeast that causes the condition.
  
  
• Immunodeficiency. People with conditions that weaken the immune system, such as acquired immune deficiency syndrome (AIDS) are more likely to develop tinea versicolor.
  
  
• Corticosteroids. A group of anti-inflammatory drugs used to provide relief for inflamed areas of the body by lessening swelling, redness, itching and allergic reactions.
  
  
• Cushing’s disease. A hormonal disorder caused by prolonged and high levels of the hormone cortisol.
  
  
• Poor nutrition.
  
  
• Pregnancy.
  
  
• Oral contraceptives.