Reviewed June 2019

I’m bleeding in between periods, could I have an infection?

I'm bleeding in between periods, could I have an infection 1200400

While bleeding between periods, or intermenstrual bleeding, is common and can happen for a variety of reasons, it can be worrying, especially when you can’t see any particular cause for it. Most periods last for between three and five days, and the average menstrual cycle lasts 28 days. However, a ‘normal’ cycle length is considered to be 21 to 34 days in adults and approximately 20 to 45 days in teenagers.1

It is worth bearing in mind that cycle length may depend on the type of contraception a woman is using, stress levels, and lots of other factors. Many other aspects of a period can also vary hugely between different women, including how heavy the period is, and the symptoms experienced alongside it, including stomach cramps, and emotional symptoms.

With all these factors to keep in mind, it can be difficult to determine the cause of your irregular bleeding, particularly if you suspect it’s down to an infection. That’s why it’s essential to learn as much as you can about how the body changes when you have an infection, or experience any other factor that could impact your menstrual bleeding.

There are lots of potential causes for intermenstrual bleeding including hormonal contraception, STIs, and cervical problems. Starting the contraceptive pill, for example, can cause bleeding between periods while the hormone levels are variable — this usually settles as the hormone levels smooth out. Having a contraceptive coil fitted, for example a hormone-releasing type such as the Mirena coil, can also cause irregular bleeding and spotting.2

Trauma to the cervix (the opening of the womb) can also cause intermenstrual bleeding – this can occur during ‘rough’ sex, following a medical procedure involving the cervix (from a smear test to a termination), or might even happen spontaneously if a woman has an ectropion, when an area of cells usually found inside the cervix appears on the outside. This is completely harmless and quite common in women of childbearing age, especially those on the pill. There are often no symptoms with a ectropion, but occasionally it can cause discomfort during or after sex, or increased/different discharge. Having an ectropion is not associated with cervical cancer.

Could it be an STI?

Sexually transmitted infections (STIs) can cause intermenstrual bleeding. There are lots of STIs out there, with a huge variety of symptoms, or sometimes no symptoms at all. STIs are spread via sexual contact, and it’s recommended that people get tested for STIs whenever they change sexual partners, yearly, or if they have any symptoms.

Chlamydia is one of the most common STIs, and is caused by a bacteria called Chlamydia trachomatis which is spread via genital fluids; this doesn’t necessarily mean penetrative sex, it can be spread through oral sex too. Lots of women who have chlamydia don’t get any symptoms, which is why regular testing is recommended. It can cause bleeding in between periods, changes to vaginal discharge, pain when urinating, discomfort during sex, and lots of other symptoms. Chlamydia can infect the cervix, which causes cervicitis (an inflamed cervix), making the individual cells of the cervix irritated, red and swollen,3 and therefore more likely to bleed.

Chlamydia can be tested for in the urine or by using a swab inserted into the vagina and is treated with antibiotics – either a single dose of antibiotic then and there, or a course of antibiotics for a week.

Gonorrhoea can also cause bleeding between periods, as well as lots of the symptoms described above. Again, the bleeding occurs due to cervicitis (inflammation of the cervix). Gonorrhoea very commonly causes a change in vaginal discharge, causing it to become thicker or change colour for example. Again, it is tested for using a swab and is also treated with antibiotics. Other STIs are less likely to cause bleeding in between periods, but may cause some of the other symptoms listed above.

Pelvic inflammatory disease

Chlamydia and gonorrhoea frequently infect the cervix (cervicitis) but they can also cause pelvic inflammatory disease (PID). PID occurs when the bacteria causing cervicitis travels up higher, into the womb, ovaries, or Fallopian tubes. Symptoms include all of those listed above for chlamydia, and also tummy pain, and pain during sex. PID is treated with a course of antibiotics (the exact antibiotic depends on the infection itself) and the course is often for two weeks. Due to the effects that inflammation and scarring have on the ovaries, Fallopian tubes, and womb, PID can also lead to fertility troubles. This can be avoided by protecting yourself from catching STIs (having safe sex) and being tested regularly to ensure any infections are treated early.

HPV and cervical cancer

Intermenstrual bleeding can be a sign of more serious problems, such as cervical or endometrial (womb) cancer, and for this reason I would advise that if you are having intermenstrual bleeding, or any other new or worrying symptoms, see your doctor – even if it’s only for a bit of reassurance.

Cervical cancer is very often caused by the human papilloma virus (HPV) infection, which is a sexually transmitted virus. There are around 100 different types of the virus, some of which can cause genital warts, some of which can cause cervical cancer, and some of which don’t do much at all. Lots of people, both men and women, have HPV at some point in their life and often the body gets rid of the virus, just like it fights off the common cold.

Having a high-risk strain of HPV for a period of time can increase the risk of the cells in the cervix becoming cancerous. The virus itself can’t be treated, but its effects can — genital warts can be treated in a number of ways, and pre-cancerous changes in the cervix can be picked up by a smear test (screening for cervical cancer) and treated before they become cancer. Like all tests, it’s not fool-proof, and intermenstrual bleeding should still prompt a visit to the doctor, even if you have had regular, normal smear tests. 4


Thrush is a fungal infection called candida which commonly infects the genital area, but can also infect the mouth or other areas of skin, especially in skin creases (like under the breasts or in the groin). Thrush is opportunistic, and often infects an area when the body’s defences are low — this can be caused by anything from being on antibiotics which have ‘wiped out’ all the good bacteria, to having chemotherapy which causes the immune system to function less well and increases the risk of infections. Vaginal thrush can cause itching and discomfort down below, and a change in discharge causing it to become thicker and white; often described as “cottage cheese-like”.

Thrush treatments like creams (containing the anti-fungal clotrimazole) or tablets (containing the anti-fungal fluconazole) can be bought from a pharmacy without a prescription. If you recognise the symptoms you’re having as thrush, it’s quite reasonable to buy these without seeing a doctor. However if the symptoms don’t seem quite right, if you haven’t had thrush before, or if the treatments don’t seem to work, a visit to your GP should be your next action.

Bacterial vaginosis

Bacterial vaginosis is another condition affecting the genital area, but despite it being quite common, people tend to know a lot less about it. All vaginas have normal bacteria colonising them (just like our mouths and noses) and this is a part of the body’s defence system. Bacterial vaginosis happens when these normal bacteria get disturbed and other less common bacteria become more prominent. It doesn’t generally cause bleeding, but it very commonly causes a change to vaginal discharge. It’s easily treated with antibiotics.

Urinary tract infections

Urinary tract infections (UTIs) can cause bleeding, although the blood doesn’t come from the cervix in these cases. They are common in sexually active women (although they’re not sexually transmitted). A number of bacteria can cause UTIs, most commonly bacteria which is normally found in the gut. UTIs can cause abdominal pain, burning and stinging on urination, a feeling of needing to urinate all the time, blood in the urine, and a number of other symptoms. Often, UTIs can make someone feel generally a bit rubbish and sometimes you might even have a high temperature (which can cause feeling cold as well as hot). A urine sample can be used to test for a UTI, but if you’ve got convincing symptoms then often antibiotics will be prescribed before the urine results are back. Repeated UTIs might need further investigation or lifestyle changes.

In short, bleeding in between periods can occur for a huge variety of reasons. While sometimes the cause will require medical attention, it can also be something completely harmless. The best course of action if you are experiencing bleeding between periods is to see your GP and get things checked out.

Last updated June 2019
Next update due 2021

Dr Evie Winther MBChB 

Evie is a GP registrar currently based in Yorkshire. She loves running, cycling, and going to the gym, and is passionate about encouraging involvement and equal opportunities for women in sport. She believes it is hugely important for women to have honest information about their health freely available and be able to ask questions without fear of judgement.

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  1. Adams Hillard, P.J., Menstruation in adolescents: what’s normal? The Medscape Journal of Medicine, 2008, vol 10, issue 12, pp 295
  2. FSRH Clinical Effectiveness Unit, ‘Intrauterine Contraception’, Clinical Guidance, April 2015,, (accessed 25 June 2019).
  3. Casey, P.M., et al., Abnormal cervical appearance: what to do, when to worry? Mayo Clinic Proceedings, February 2011, vol 86, issue 2, pp 147-151
  4. NHS Choices Health A-Z, ‘Cervical cancer’, [website], 2015,, (accessed 25 June 2019).

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