Canestest Results Explained: What a Yellow, Blue or Green Swab Means
How to use the Canestest self-test, what each result means, when it can mislead you, and what to do next.
Part of our Bacterial Vaginosis condition guide.
Get medical help first. Contact NHS 111 (NHS 24 on 111 in Scotland) or your GP the same day if you have pain in your lower tummy or pelvis, a high temperature or you feel unwell. If you’re pregnant, speak to your midwife about any change in discharge. Visit a sexual health clinic if you have bleeding between periods or after sex, sores or blisters, or your symptoms started after sex with a new partner. Online treatment is not suitable in these situations.
Key fact: Canestest measures vaginal pH, not infection. No colour change means your pH is normal, which fits thrush if you’re itchy. A blue or green tip means your pH is raised, which usually points to bacterial vaginosis (BV).
Result Points to BV? Get Assessed Online
Access Doctor’s GPhC-registered pharmacist independent prescribers assess BV symptoms online and, where treatment is suitable, supply it from our UK pharmacy. You don’t need a test result to start. Approved before 3pm, Monday to Friday? Dispatched the same day in plain packaging, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start BV Consultation →Adults only online, and not in pregnancy or breastfeeding. Access Doctor’s online BV service is for adults aged 18 and over who aren’t pregnant or breastfeeding. If that isn’t you, your GP, midwife or a local sexual health clinic can assess and treat BV free of charge. Under 18? NHS sexual health clinics see young people confidentially.
What Canestest is
Canestest is a Canesten-brand self-test for vaginal infections. Each pack contains one swab with a pH-sensitive tip. It doesn’t look for bacteria or yeast. It measures how acidic your vagina is, and that one reading is surprisingly useful.
A healthy vagina is mildly acidic, at a pH of roughly 3.8 to 4.5, because protective lactobacilli produce lactic acid. In bacterial vaginosis, those lactobacilli are crowded out and the pH rises above 4.5. In thrush, the pH usually stays normal. So a pH test helps you tell the two apart before you spend a week on the wrong treatment.
3.8–4.5
Normal vaginal pH
Above 4.5
Typical pH in BV
10 secs
Before you read the swab
How to use Canestest
Most wrong results come from testing at the wrong time, not from the technique. These are the general steps; always follow the leaflet in your pack.
1
Check it’s the right time
Not during your period or with any bleeding, not within 12 hours of sex or douching, and not while you’re using a vaginal cream, gel or pessary.
2
Wash your hands and unwrap the swab
Hold it by the handle and don’t let the yellow tip touch anything.
3
Insert the tip and turn it gently
Insert only as far as the marked handling points, and rotate it so the tip touches the vaginal wall. Then remove it.
4
Read it after 10 seconds
Look at the tip in good light and compare it with the chart in the leaflet.
Reading your result
| Swab tip | What it means | Most likely, with symptoms |
|---|---|---|
| Stays yellow (no colour change) | Normal vaginal pH | Thrush, if you have itching and thick white discharge |
| Turns blue or green | Raised vaginal pH | BV, if you have thin grey or white discharge and a fishy smell |
| Blue or green, with frothy yellow-green discharge or a new partner | Raised vaginal pH | Possibly trichomoniasis, an STI that needs clinic testing |
The result is a pointer, not a diagnosis. Read it alongside your symptoms. A raised pH with the classic fishy smell is a strong sign of BV. A raised pH with no symptoms at all usually doesn’t need treatment.
When the result can mislead you
Honestly, this is the bit most people skip, and it’s where most confusing results come from.
- Periods and bleeding — blood raises pH, so testing during or around your period can show blue or green when you don’t have BV.
- Recent sex or douching — semen and washes change pH for hours. Wait at least 12 hours.
- Vaginal products — creams, gels, pessaries and lubricants can all affect the reading.
- After the menopause — vaginal pH is naturally higher, so a raised result can be a false alarm. Don’t rely on the test.
- Pregnancy — speak to your midwife or GP before testing, and about any change in discharge.
Canestest doesn’t test for STIs. Chlamydia and gonorrhoea often cause no symptoms and don’t reliably change pH. If you’ve had a new partner, or you have pain, bleeding after sex or sores, get tested at a sexual health clinic whatever the swab shows.
BV or thrush: matching the result to your symptoms
| Bacterial vaginosis | Thrush | |
|---|---|---|
| Discharge | Thin, white or grey | Thick, white, like cottage cheese |
| Smell | Fishy, often worse after sex | Usually none |
| Itching and soreness | Usually little or none | Common, often intense |
| Canestest | Blue or green (raised pH) | No colour change (normal pH) |
| Treatment | Prescription antibiotic | Antifungal, available from pharmacies |
Our guides to BV symptoms, discharge and smell and BV vs thrush go into more detail. If the picture is mixed, our guide on how to test for BV at home explains what a pH test can and can’t tell you.
What to do next
1
Blue or green, with BV symptoms
You’ll need a prescription antibiotic. The usual first choice is metronidazole tablets, twice a day for 7 days. Our guide to BV treatment options compares tablets, gel and cream.
2
No colour change, with itching
Thrush is likely, and a pharmacy antifungal is the usual treatment. See our thrush treatment options. If it hasn’t helped within a week, get assessed.
3
Result doesn’t match your symptoms
Don’t keep guessing. A GP or sexual health clinic can examine you, test properly and check for STIs.
4
BV keeps coming back
If you’ve had BV more than 4 times in a year, see your GP or a sexual health clinic. Our guide to recurrent BV explains the options.
Get Assessed for BV Online
Complete a short online consultation and a GPhC-registered pharmacist independent prescriber will check whether your symptoms sound like BV and whether treatment is suitable. Approved before 3pm, Monday to Friday? Dispatched the same day in plain packaging, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose.
Start BV Consultation →UK safety and getting treatment
Every antibiotic treatment for BV in the UK, whether tablets, gel or cream, is a prescription-only medicine. Before anything is prescribed, a GPhC-registered pharmacist independent prescriber reviews your consultation, including your allergies and the other medicines you take. Always read the patient information leaflet in the pack. Never share antibiotics with anyone else, and don’t keep leftover tablets for next time: return unused medicine to a pharmacy.
If you think you’ve had a side effect from a medicine, tell your pharmacist or doctor. You can also report it to the MHRA through the Yellow Card scheme, which helps keep medicines safe for everyone.
You can get BV treatment free from your GP or a sexual health clinic, and many clinics offer walk-in appointments and STI testing at the same visit. Our private online service is an alternative for adults aged 18 and over who aren’t pregnant or breastfeeding. You can see all our BV treatment online options on one page.
Frequently Asked Questions
What does Canestest test for?
Canestest measures the acidity (pH) of your vagina. It doesn’t detect bacteria or yeast directly. A normal pH with itching and thick white discharge points towards thrush, while a raised pH points towards bacterial vaginosis (BV) or, less often, trichomoniasis.
What does a blue or green Canestest result mean?
A blue or green tip means your vaginal pH is raised. Alongside thin grey or white discharge and a fishy smell, that makes BV likely, and BV needs a prescription antibiotic. A raised pH can also be caused by trichomoniasis, a sexually transmitted infection, so frothy yellow-green discharge or a new partner means you should get tested at a sexual health clinic.
What if the Canestest swab stays yellow?
If the tip doesn’t change colour, your pH is normal. If you have itching, soreness and a thick white discharge, thrush is the likely cause and a pharmacy antifungal is the usual treatment. If your symptoms don’t fit thrush, or an antifungal doesn’t help within a week, get assessed rather than guessing.
How accurate is Canestest?
Canestest is good at one job: showing whether your vaginal pH is raised, which helps separate BV from thrush. It isn’t a diagnosis. It can’t tell BV from trichomoniasis, it doesn’t test for other STIs, and testing at the wrong time can give a false result.
When should I not use Canestest?
Don’t test during your period, around the days just before or after it, or if you have any bleeding. Wait at least 12 hours after sex or douching, and don’t test while using any vaginal cream, gel or pessary. Don’t rely on it after the menopause, and speak to your midwife or GP first if you’re pregnant. Always follow the timings in the leaflet.
Can I use Canestest if I’m pregnant?
Speak to your midwife or GP before testing, and about any change in discharge in pregnancy. BV in pregnancy should be assessed and treated by a clinician who knows you’re pregnant. Our online service doesn’t treat BV in pregnancy.
Can I have thrush and BV at the same time?
Yes, though it’s less common. A home pH test may only pick up the BV, because BV raises pH and thrush doesn’t. If you have both itching and a fishy-smelling discharge, or treatment for one doesn’t clear your symptoms, get assessed by a GP or sexual health clinic.
What should I do after a positive BV result?
If your result is blue or green and you have typical BV symptoms, you’ll need a prescription antibiotic. The usual first choice is metronidazole tablets twice a day for 7 days. You can get this from your GP, a sexual health clinic or a regulated online service like ours, if you’re 18 or over and not pregnant or breastfeeding.
Can I buy Canestest from Access Doctor?
Canestest is currently out of stock with us. You don’t need a test to start a BV consultation: our pharmacist prescribers assess your symptoms and will tell you if BV sounds unlikely or you’d be better seen in person.
Treatment after your result
If your result and symptoms point to BV, an online consultation with a pharmacist independent prescriber is the next step. If they point to thrush, an antifungal is the right treatment instead. The Canestest self-test itself is currently out of stock with us.
Bacterial vaginosis · Rx
Metronidazole 400mg Tablets
The usual first-choice BV treatment: one tablet twice a day for 7 days, after an online consultation.
View →Thrush
Thrush Treatment
If your symptoms or test point to thrush rather than BV, see our thrush treatments.
View →Bacterial vaginosis
BV Treatment Online
All our BV options in one place, including when to see your GP or a sexual health clinic instead.
View →References
- National Institute for Health and Care Excellence. Clinical Knowledge Summaries: Bacterial vaginosis. cks.nice.org.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summaries: Candida — female genital. cks.nice.org.uk
- NHS. Bacterial vaginosis. nhs.uk
- NHS. Thrush in women. nhs.uk
- West of Scotland Sexual Health MCN. Bacterial vaginosis guideline (June 2025). wossexualhealthmcn.scot.nhs.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Canestest is a screening aid, not a diagnosis. Always consult a qualified healthcare professional if you are unsure about your symptoms or result. In a medical emergency, call 999.