There are three vaginal infections that are typically classified as vaginitis. The most common of these is bacterial vaginosis (BV). BV is caused by an overgrowth of one of several organisms (bacteria) that are usually present in the vagina. Normally, the “good” bacteria in the vagina outnumber the “bad” bacteria. However, if the bad bacteria become too abundant, they can upset the bacterial – or pH – balance of the vagina, resulting in BV.

Although BV accounts for more cases, it is less understood than yeast infection or trichomoniasis, the other common types of vaginitis. It is also undetected and misdiagnosed more often than these conditions. Left untreated, BV can lead to the following significant health complications:

• Pelvic inflammatory disease (also known as PID, an infection of the upper genital tract that may cause infertility)
  
  
• Complications following surgeries (abortion, hysterectomy and other procedures)

Experts also believe that BV may be associated with increased susceptibility to the human immunodeficiency virus (HIV), the virus that causes acquired immune deficiency syndrome (AIDS). However, further study is needed to confirm this link.

According to the Centers for Disease Control and Prevention, BV affects up to 16 percent of expectant mothers in the United States, although many are not even aware they have the condition. Pregnant women with BV are at increased risk of the following:

• Premature delivery
• Postpartum infection
• Post-surgical complications (after Caesarean-section)

Although BV can be transmitted through sexual intercourse, it is not generally considered a sexually transmitted disease (STD). Approximately one-quarter of women treated for BV will have a recurrence within one month.

The two other main types of vaginitis include:

• yeast infection (genital candidiasis). Caused by an overabundance of Candida, a microscopic fungus that normally inhabits the vagina. There are four types of Candida. A variety called Candida albicans (C. albicans) causes the vast majority of vaginal yeast infections. This fungus, which also grows normally in the mouth (a condition called thrush) and digestive tract, can infect other moist regions of the body as well, including the skin folds and nail beds.
  
  Almost 75 percent of all adult women will have a yeast infection at some point in their lives, according to the CDC, and approximately 5 percent of patients will develop a condition called recurrent vulvovaginal candidiasis (RVVC). RVVC is classified as more than three symptomatic vaginal yeast infections over the course of one year. Patients who experience RVVC should notify their gynecologist (a physician that specializes in treating disorders of the female reproductive system) who will attempt to identify the underlying cause of the condition. Although yeast infection is not generally considered an STD, it may be transmitted to male partners through sexual intercourse in rare instances.
  
  
• trichomoniasis. Caused by a parasite in the vagina, typically the Trichomonas vaginalis. This protozoan (single-cell organism) primarily resides in a woman’s genitourinary tract, where it finds the moisture and warmth it needs to develop and multiply. Trichomoniasis is typically transmitted through sexual intercourse with a partner who is already infected. Because the parasite can live for several hours on damp washcloths, towels and bathing suits, it can be spread when these items are shared. Trichomoniasis affects approximately 5 to 10 percent of women in the United States.
  
  Trichomoniasis affects more people (an estimated 7.4 million) than any other nonviral STD in the United States. Left untreated, trichomoniasis does not typically produce symptoms. However, it may cause vaginitis in some women, and some men with the condition may develop nongonococcal urethritis (a type of urethral infection). Additionally, recent research indicates that pregnant women with trichomoniasis may experience preterm delivery, and individuals who are infected may be two to four times more likely to acquire other STDs, including HIV. However, more research is needed.

Other, less common forms of vaginitis include:

• Atrophic vaginitis. Typically results from a decline in estrogen (a female reproductive hormone) levels occurring after menopause. Reduction of the hormone may cause changes in the skin around the vagina, vulva, urethra and/or bladder.
  
  
• Noninfectious vaginitis. Occurs when products such as perfumed soaps, douches and vaginal sprays irritate the skin around the vagina or cause an allergic reaction.
  
  
• Chlamydia. Primarily transmitted through sexual intercourse.
  
  
• Viral vaginitis. Caused by viral infection, such as the herpes simplex virus (HSV) or the human papillomavirus (HPV).