14 Causes of Bacterial Vaginosis

2. Unprotected Oral Sex

Unprotected oral sex can affect the balance of bacteria in your vagina. The mouth carries many types of bacteria and during oral contact, some of these bacteria can move into the vaginal area. Your vagina stays healthy when helpful bacteria stay in control. Oral contact can change the vaginal pH since saliva has a different pH than the vagina. This change can allow harmful bacteria to grow.

Small cuts or sores in the mouth can raise this risk. Bleeding gums, mouth sores, or recent dental work can make it easier for bacteria to pass during contact. You may not notice these issues at the time. Oral sex also spreads bacteria from other body areas, including those linked to the anus or skin. Even small amounts can disrupt your normal balance.

You may not notice symptoms right away. Changes can happen over days as bacteria shift. This process does not mean oral sex causes an infection every time. Using barriers during oral sex can limit bacterial transfer. Clean habits before and after sexual contact also help reduce changes in vaginal balance.

3. Unprotected Anal Sex

Unprotected anal sex can raise your risk of bacterial vaginosis (BV). Bacteria from the rectum can move into the vagina during anal sex. The rectum holds many bacteria that do not belong in the vagina. During anal sex, these bacteria can spread to nearby skin and surfaces. If vaginal contact follows, the bacteria can enter the vagina.

This transfer can upset the normal balance of vaginal bacteria. The vagina works best when helpful bacteria stay in control. Outside bacteria can reduce those helpful bacteria and allow other types to grow.

You face higher risk when you move from anal to vaginal contact without cleaning or changing protection. Bacteria can travel on skin, fingers, or sex toys. Even small amounts can matter. Semen can also affect vaginal balance. It can raise vaginal pH levels, which makes it easier for harmful bacteria to grow. When this combines with bacteria from anal contact, the risk increases.

4. Sex with Unseen Risks

Sex can change the balance of bacteria in your vagina in ways you cannot see. Even when you feel fine, these changes can raise the chance of bacterial vaginosis. BV is not a classic sexually spread infection, but sexual contact still plays a role. You may notice higher risk when you have a new partner or more than one partner. Each person carries their own mix of bacteria. During sex, these bacteria can enter your vagina and shift the balance between helpful and BV-associated bacteria.

Semen can also affect this balance. It has a higher pH than the vagina. When semen enters the vagina, it can raise the pH level and allow harmful bacteria to grow more easily. Certain sexual activities can add to the risk, including moving from anal or oral contact to vaginal contact without cleaning in between and sharing sex toys without cleaning. You may also see risk differences based on partner type. BV occurs more often in people with female partners, likely due to shared vaginal bacteria during close contact.

5. Multiple Sexual Partners

Having multiple sexual partners can raise your risk of bacterial vaginosis. Each partner can introduce different bacteria. These bacteria can change the natural balance inside your vagina. Your vagina works best when healthy bacteria stay in control. Frequent exposure to new partners can disturb this balance. When harmful bacteria grow faster, bacterial vaginosis can develop.

You can get bacterial vaginosis even if you do not have sex often. Still, the risk tends to rise as the number of partners increases. This pattern appears in people with male partners, female partners, or both. Sex without condoms can also affect your risk. Condoms help limit the exchange of fluids and bacteria. Without them, bacteria can move more easily between partners.

Bacterial vaginosis is not considered a classic sexually transmitted infection. You do not catch it from one person alone. Instead, it develops when changes in sexual activity upset the normal bacterial mix.

6. Improper Condom Use

Improper condom use can raise your risk of bacterial vaginosis. Condoms help limit the exchange of fluids that can change the balance of bacteria in your vagina. When condom use is inconsistent or incorrect, that balance can shift.

Semen has a higher pH than the vagina. When semen enters the vagina without a condom, it can raise vaginal pH. A higher pH makes it easier for harmful bacteria to grow and crowd out Lactobacillus, particularly Lactobacillus crispatus, the helpful bacteria that protect vaginal balance.

Improper use includes condoms that break, slip off, or get put on late. It also includes removing a condom before sex ends. These situations allow fluid contact that affects vaginal bacteria. Using oil-based products with latex condoms can cause damage. Damage reduces protection and increases the chance of fluid exchange. Even small tears can matter.

Switching between protected and unprotected sex can also affect bacterial balance. Your vagina responds to changes in fluids and bacteria. Frequent shifts make it harder to keep a stable environment.

7. Overcleaning of the Vagina

You may think frequent washing keeps the vagina clean, but overcleaning can upset its natural balance. The vagina cleans itself by keeping helpful bacteria in control. When you wash too often, you can remove these helpful bacteria.

Soaps, washes, and sprays can change the normal acid level inside the vagina. This shift makes it easier for harmful bacteria to grow. When harmful bacteria grow faster than helpful ones, bacterial vaginosis can develop.

Overcleaning often includes actions that seem harmless but these actions can slowly change the vaginal environment. Common overcleaning habits involve scented soaps or washes used inside the vagina and rinsing the inside of the vagina with water or other products. They also involve cleaning the vaginal area many times a day and frequent use of wipes meant for internal use.

You may notice dryness, irritation, or a change in discharge after frequent cleaning. These signs can show that the natural balance has shifted. The vagina works best when its normal bacteria stay in place.

8. Over-Douching

Over-douching can upset the natural balance of bacteria in your vagina by washing out helpful bacteria that normally protect you. This allows harmful bacteria to grow more easily, which can lead to bacterial vaginosis. The vagina does not need internal cleaning to stay healthy.

Douching also changes the normal acid level in your vagina, which helps control which bacteria survive. When it shifts, harmful bacteria can take over. Many people think douching removes odor or discharge. In reality, it can make these problems more likely. The wash may mask smells for a short time, but it does not fix the cause. Over-douching can also push bacteria deeper into the vagina. This movement increases the chance of imbalance. Once the balance shifts, symptoms like odor or discharge may appear.

Some products sold for douching contain scents or chemicals and can irritate vaginal tissue, which makes it easier for harmful bacteria to grow. You may notice bacterial vaginosis coming back if douching continues. Even after treatment, the imbalance can return. Repeated disruption keeps the vaginal environment unstable.

9. Previous Bacterial Vaginosis

If you have had bacterial vaginosis before, you have a higher chance of getting it again. Your vaginal bacteria may not fully return to a stable balance after treatment. This makes it easier for harmful bacteria to grow again. BV can come back weeks or months later, even if you finished treatment. Treatment often reduces symptoms but does not always change the conditions that allowed BV to start. Changes in vaginal bacteria can repeat over time.

Your body may react differently after a past infection. The vagina can become more sensitive to pH changes, such as exposure to semen or menstrual blood. These changes can lower the amount of healthy bacteria that help protect you. Treatment usually involves a class of antibiotics that lower harmful bacteria. This does not always rebuild healthy bacteria right away.

10. Lowered Immune System Combined with Other Risk Factors

Your immune system helps keep balance in your vagina, but when it weakens, helpful bacteria may drop while harmful bacteria grow faster. Ongoing stress, poor sleep, low nutrition, certain health conditions, and treatments that reduce immune response can make it harder for your body to control bacteria.

Other risk factors can add pressure when immune defenses are already strained. These include frequent antibiotic use that lowers helpful bacteria and hormone changes during pregnancy or the menstrual cycle. Vaginal practices that wash away natural bacteria and smoking, which can interfere with immune response, can further disrupt balance.

When several of these factors occur at the same time, the vaginal environment may struggle to return to a healthy state. This overlap often explains why bacterial vaginosis develops during periods of physical or hormonal stress rather than from one cause alone. Recovery may also take longer when immune strength remains reduced.

11. Affected Underwear Improperly Cleaned

Underwear sits close to your vagina all day and can change the balance of bacteria if it stays damp or holds leftover fluids. Improper cleaning leaves behind sweat, discharge, or traces of stool, which allows unwanted bacteria to move and grow.

Detergent residue can also irritate your skin and affect normal bacteria. Moisture and warmth from damp underwear help bacteria multiply and upset the natural balance inside your vagina.

Shared laundry spaces can spread bacteria through wash water if cleaning is not thorough. This repeated exposure to affected underwear can make it harder for your vagina to maintain a healthy balance. Fabric type, tight fit, and long wear times can also trap heat and moisture, further supporting bacterial growth and slowing recovery.

12. Regular Sex

Regular sex can affect the balance of bacteria in your vagina, which helps keep the area healthy. During sex, fluids from another person mix with your natural fluids and can change your vagina’s acidity, which makes it easier for certain bacteria to grow.

Regular sexual activity can disrupt this balance over time and raise the chance of bacterial vaginosis, especially if your body is sensitive to changes. This disruption can occur through several physical and chemical changes during sexual contact. Semen can raise vaginal pH levels and skin contact can move bacteria from one area to another. Repeated friction can irritate vaginal tissue and make it easier for bacterial balance to shift.

This risk varies from person to person and depends on your natural chemistry, hormone levels, and immune response. Symptoms may appear days or weeks later, which makes the cause harder to identify.

13. Untreated STDs

Untreated sexually transmitted diseases can raise your risk of bacterial vaginosis by changing the balance of bacteria in your vagina. Some STDs cause swelling, irritation, or extra fluid, which makes it harder for healthy bacteria to survive. Common STDs linked to this problem include chlamydia, gonorrhea, and trichomoniasis.

These infections can alter vaginal tissue and fluid levels even when symptoms are mild or absent. Inflammation and excess moisture change the environment inside the vagina, which weakens helpful bacteria and allows harmful bacteria to gain control over time.

Many infections stay silent while still affecting your vaginal environment. Without treatment, the infection continues to disrupt normal bacteria and raises the chance of BV. Having BV can also make it easier to get or pass an STD, and this creates a cycle where one condition supports the other. Regular testing and early care help limit long-term changes and lower the chance that untreated STDs will trigger or worsen bacterial vaginosis.

14. Sex With an Affected Woman

Sex with a woman who has bacterial vaginosis can raise your chance of developing it, especially if your partner has symptoms. Vaginal fluids can transfer bacteria during sexual contact, which upsets the natural balance in your vagina and allows harmful bacteria to grow. Relationships between women may have a higher risk, particularly when sharing sex toys or having direct genital contact without proper cleaning.

Bacterial vaginosis is not a classic sexually transmitted infection, but sexual activity can trigger it by moving bacteria into a new environment. Your body may react by changing its normal bacterial mix.

You can have bacterial vaginosis even if your partner has no symptoms. Many women carry the bacteria without discomfort, odor, or discharge, which makes it hard to know when exposure has occurred. Repeated contact with an affected partner can increase recurrence. Even after symptoms clear, the vaginal balance can remain sensitive, and new exposure can disrupt it again without warning.