Condoms apart from preventing unwanted pregnancies and transmission of STIs, condoms do help good bacteria grow in the vagina.
Sexually active women in the study who used condoms had larger colonies of beneficial microbes in their vaginas compared with women who used other forms of birth control, the researchers at Beijing Friendship Hospital found.
The scientists focused on lactobacillus, a group of bacteria that dominates the natural flora of the vagina for many women.
The microbes, which produce lactic acid and hydrogen peroxide, help the vagina maintain an average pH of 4.5, comparable to the acidity of beer or tomato juice, the Huffington Post reported.
This "acidic buffer system," as the researchers called it, is thought to block harmful bacteria from taking up residence and causing infections.
Though there may not be a "normal" microbiome for a healthy vagina, the presence of lactobacillus is thought to help prevent bacterial vaginosis, which is an imbalance of vaginal bacteria that causes itching, unusual discharge and unpleasant odor.
Beneficial bacteria have even been linked to a decreased risk of human immunodeficiency virus (HIV) infection.
The study is published online in the journal PLOS One.