Vaginal thrush happens when a usually harmless yeast in the vagina overgrows and starts causing symptoms like itching, soreness and discharge.

Quick Scoop: What actually causes vaginal thrush?

At the core, vaginal thrush is caused by an overgrowth of a fungus called Candida (most often Candida albicans), which normally lives in small amounts in the vagina, bowel, mouth and on the skin without causing problems. Thrush itself is not classed as a sexually transmitted infection, but sex can sometimes trigger symptoms or pass it on.

Think of the vagina as a delicate ecosystem: it contains “good” bacteria and a small number of yeasts, all kept in balance by hormones, immune defences and pH (acidity). When something tips that balance, candida can multiply and cause thrush.

Main medical causes and triggers

These are the most commonly recognised factors that make thrush more likely by disrupting that natural balance:

  • Recent antibiotic use: Antibiotics kill helpful vaginal bacteria that normally keep yeast under control, so candida can overgrow more easily.
  • Hormonal changes and high oestrogen:
    • Pregnancy and breastfeeding.
* The combined oral contraceptive pill (especially higher-dose) and hormone replacement therapy (HRT).

* Natural menstrual cycle changes in some people.
  • Diabetes and blood sugar issues:
    • Poorly controlled diabetes raises sugar levels in vaginal secretions, which yeast thrives on.
  • Weakened immune system:
    • Conditions like HIV, immune disorders, or medicines such as chemotherapy or strong immunosuppressants reduce the body’s ability to keep candida in check.
  • Local skin and irritation factors:
    • Pre‑existing vulval skin conditions like eczema, psoriasis or jock itch.
* Soaps, shower gels, scented products or harsh detergents that irritate the vulva and vaginal area.

* Tight, non‑breathable clothing that keeps the area warm and moist. (Warm, moist conditions favour candida growth.)
  • General high‑oestrogen or health states:
    • Iron deficiency and other general health issues can play a background role for some people.

In many cases, more than one trigger is present at the same time – for example, someone who is pregnant, on antibiotics and wearing very tight synthetic underwear.

Is vaginal thrush sexually transmitted?

  • Thrush is not classified as a sexually transmitted infection (STI).
  • However:
    • Sex can sometimes trigger symptoms because of friction, irritation or changes to the local environment.
* It can occasionally be passed between partners, particularly with oral–genital or genital–genital contact, but this is not the main way it develops.

If symptoms keep returning after sex, it may be worth both partners being checked and treated if needed.

Why you might keep getting thrush (recurrent thrush)

Some people have recurrent vaginal thrush, meaning repeated episodes over time. Often, the root causes are:

  1. Underlying factors not fully addressed
    • Undiagnosed or poorly controlled diabetes.
 * Ongoing use of high‑dose oestrogen contraception or HRT.

 * Immune system problems or medications.
  1. Persistent local irritation
    • Continual use of perfumed soaps, wipes, bubble baths or panty liners, which keep irritating the vulval skin.
 * Very tight or synthetic underwear or sportswear trapping heat and moisture.
  1. Incorrect diagnosis
    • Other conditions, like bacterial vaginosis, dermatitis, STIs or vulval skin disorders, can mimic thrush and may be missed if you’re self‑treating repeatedly without a swab or exam.

Everyday factors that can tip the balance

While not all of these are formally “proven”, they frequently appear in clinical guidance and patient information as possible contributors or triggers:

  • Heat and sweat in the genital area (e.g., wearing wet swimwear for long periods, intense exercise without changing out of damp clothes).
  • Using panty liners or pads daily, especially scented ones, which can keep the area warm, moist and slightly irritated.
  • Strongly perfumed laundry products used on underwear.
  • High‑sugar diets might worsen symptoms in some people with recurrent thrush, especially if they have or are at risk of diabetes, although evidence is mixed.

An example: someone on a broad‑spectrum antibiotic for a chest infection, working long shifts in tight gym leggings, then using scented shower gel on the vulva, might suddenly notice itching and thick discharge a few days later.

What this isn’t caused by

There are also some common myths:

  • Poor hygiene: Thrush is not a sign of being “dirty”; in fact, over‑washing with harsh soaps and scrubbing can make it more likely.
  • Only sexually active people: Vaginal thrush can occur in people who are not sexually active at all.
  • Only “older” women: It can affect teens through to post‑menopausal women; hormone levels and other risk factors matter more than age alone.

When to see a doctor

You should see a doctor, nurse, or sexual health clinic if:

  • This is your first time with symptoms and you’re not sure it is thrush.
  • You get thrush very often (for example, four or more times a year).
  • Symptoms don’t improve with standard thrush treatment or keep coming back soon after treatment.
  • You have other symptoms such as unusual bleeding, pelvic pain, fever, or a foul‑smelling discharge.
  • You are pregnant, have diabetes, or have a weakened immune system and think you have thrush.

A clinician can take a vaginal swab to confirm candida, rule out other infections and look for underlying causes if it keeps recurring.

Bottom note

Information gathered from public forums or data available on the internet and portrayed here.