What Causes Vaginal Imbalance?

What causes vaginal imbalance?

A healthy vaginal microbiome is usually dominated by Lactobacillus bacteria, which produce lactic acid and keep the pH low, at around 3.5 to 4.5. Imbalance, sometimes called vaginal dysbiosis or bacterial vaginosis (BV), happens when those protective bacteria fall away and the pH rises. The most common triggers are:

• Antibiotics, which can clear helpful bacteria along with harmful ones
• Hormonal changes across your cycle, pregnancy, and menopause
• Sexual activity, especially with a new or different partner
• Douching and perfumed washes, soaps, or sprays
• Some forms of contraception
• Smoking, stress, and diet

Because the vaginal microbiome is so responsive, these often add up over time, and even small everyday changes can shift the balance.

How do antibiotics affect vaginal balance?

Antibiotics treat harmful bacteria, but they can also reduce the protective Lactobacillus bacteria in the vagina at the same time. With fewer lactobacilli holding the balance, other bacteria or yeast may have more room to grow, which is why some people notice thrush or BV-type symptoms during or after a course.

Balance often recovers on its own, but it can take time, and imbalance can return even after BV has been treated. That is one reason antibiotics matter when they are genuinely needed, but are worth using only when necessary.

How do hormones and your menstrual cycle affect it?

Your hormones, especially oestrogen, have a strong influence on the vaginal microbiome. Oestrogen helps vaginal cells build up glycogen, which lactobacilli feed on, so higher oestrogen tends to support a Lactobacillus-rich, protective environment.

This is why balance can shift at different points in life:

• Your period: Menstrual blood is less acidic, so pH rises during your period and Lactobacillus levels can dip temporarily.
• Pregnancy: Higher oestrogen usually supports a stable, Lactobacillus-dominant microbiome.
• Menopause: As oestrogen falls, glycogen and lactobacilli tend to decline and pH rises, which is linked to dryness and a greater chance of imbalance.

These shifts are normal, and the microbiome often settles as hormones do.

How does sex affect vaginal balance?

Sex can influence the vaginal microbiome in a few ways. Semen is alkaline, so it temporarily raises vaginal pH and can reduce the protective effect of lactic acid. Having a new partner or more than one partner is also associated with a higher chance of imbalance, as it can disturb the normal mix of bacteria.

BV is not classed as a sexually transmitted infection, but sexual activity can trigger it. Using condoms is linked to a lower risk, and is one simple thing that may help.

Can washing, douching, and scented products upset the balance?

Yes. The vagina cleans itself, so washing inside it or using scented products can disrupt its natural balance. Douching in particular can flush out protective bacteria and is associated with a higher risk of BV.

The NHS suggests avoiding vaginal douches and washes, perfumed soaps, bubble bath and shower gel around the vulva, and strong detergents on underwear. Using plain warm water, or water and a plain unscented soap on the outside only, is gentler on the balance.

Can birth control affect vaginal balance?

Contraception can play a role, though the picture is mixed. Some evidence links combined hormonal contraception, which contains oestrogen, with a more stable Lactobacillus-dominant microbiome. Other options can go the other way, and using an intrauterine device (IUD) is listed by the NHS as something that can make BV more likely, particularly if you already get unusual discharge.

If you notice symptoms that seem to line up with starting a new method, it is worth discussing with your doctor rather than stopping on your own.

What other everyday factors can affect it?

Beyond the big triggers, a few other things can influence the vaginal microbiome over time:

• Smoking: Tobacco use is associated with changes in vaginal bacteria and a higher risk of imbalance.
• Stress: Ongoing stress may affect the balance through its effects on hormones and immunity, though this is still being studied.
• Diet: General diet and blood sugar can play a part, and recurrent thrush is more common when blood sugar is high.
• Period products and moisture: Leaving tampons in too long, or staying in damp underwear or gym wear, can create conditions some microbes prefer.

These tend to build gradually, which is why steady, gentle habits usually matter more than any single fix.

What are the signs of vaginal imbalance?

If the balance has shifted, you may notice changes like unusual discharge, a different or fishy smell, itching, or irritation. These are more meaningful when they appear together or keep returning rather than as a one-off.

→ 6 Signs of an Imbalanced Vaginal Microbiome (and What They Mean)

How do you support a healthy vaginal balance?

The encouraging part is that many of these triggers are within your control. Washing gently with water only, avoiding douches and scented products, using condoms with new partners, not smoking, and using antibiotics only when needed all help protect your natural balance over time. Because everyone's microbiome is different, testing yours can show you your own starting point.

→ How to Support a Healthy Vaginal Microbiome: The Complete Guide
→ What Is the Vaginal Microbiome, and Why Does It Matter?
→ The Vaginal Microbiome Through Life: What Changes and Why