Why do we bleed on our periods?

During our periods, the uterus sheds the endometrium, but why does this uterine lining come out as blood?

Why Do We Bleed On Our Periods?
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Why Do We Bleed On Our Periods?

Every month like clockwork, we get toride the crimson tide.While our body once again gets ready to rid itself of the uterine lining, we prepare our tampons, pads, menstrual cups, panties and put away any white trousers. But why is it that we bleed on our periods? The last time we checked, the endometrium was a solid, not a liquid.

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What is a period?

Every month the body prepares itself for pregnancy. This means maturing an embryo ready for fertilisation and creating a thick endometrium packed full of nutrients to receive the fertilised embryo.

If you don’t happen to get pregnant, then the thick endometrium that your body spent all this time building gets sloughed away, taking the unfertilised egg with it. This is what is known as your period.

The period usually occurs around the first to the fifth day of the menstrual cycle (or about 14 days after ovulation) but can be longer depending on the person. Most people will begin their period around the ages of 10-18 and will continue to experience them every month until they reach menopause around 45-55.

What is in period blood?

The reason we bleed on our period lies in knowing what is in our menstrual blood. The endometrium holds lots of blood cells to support a potential embryo. So, when the endometrium sheds, the small blood vessels that run through it get ruptured; this tissue and blood are released in our period.

Those aren’t the only components of our menstrual blood; clots are also common for many people. While clots can be scary, they’re totally normal and are just a sign that the body is trying to slow the blood flow. Although unusually heavy bleeding or very large clots can be a sign of menorrhagia and a doctors consult will be required.

What different types of period blood mean

Period blood greatly differs from person to person and can say quite a lot about your health. We can have shorter or longer periods, lighter or heavier flows, and our period blood can even come in various colours.

Bright Red

Bright red period blood is the sign of a regular or fresh flow. Some people find that their period starts bright red and slowly gets darker as their period starts to end. Others find that their period blood stays this red colour the whole time.

Very rarely, bright red blood between periods can be an indication of cervical cancer. Other symptoms of cervical cancer include:

  • Heavy periods
  • Periods that last longer than usual
  • Bleeding after sex
  • Pain in lower back, stomach or legs
  • Loss of appetite
  • Foul-smelling vaginal discharge
  • Unexplained weight loss

Brown or Dark Red

Brown or dark red blood may often happen at the very beginning or end of your cycle. This blood is merely older and has had more time to oxidise.

If you have brown or dark red spotting between your period, this could also be a sign of early pregnancy known as spotting. If you are already pregnant and find yourself bleeding brown or dark red blood from the vagina, this could be a sign of miscarriage or an ectopic pregnancy. In either case, you should check with a doctor to be sure.


Pink menstrual blood can happen for people who use birth control that lowers oestrogen. Lowered oestrogen levels can cause lighter flow with a pinkish colour. Pink periods can also be a sign of anaemia.

Sex can also create micro-tears in the vagina or cervix. Period blood then can mix with the cervical fluid giving it a lighter colour.

If you find yourself spotting pink blood between your periods, this could also be an early sign of pregnancy, and a doctor’s appointment may be required.


Not unlike pink blood, orange menstrual blood could also occur when the period mixes with the cervical fluid.

Orange period blood could indicate an infection such as bacterial vaginosis or an STD. In this case, look out for other symptoms such as itching or foul-smelling discharge and book an appointment with your doctor or gynaecologist.


Grey period blood is also a telltale sign of bacterial vaginosis, an infection that happens when there is an imbalance of good and bad bacteria in the vagina. Look out for other symptoms such as itching, painful or burning urination and foul-smelling discharge and book an appointment with your doctor.


Black period blood, not unlike brown or dark red, is a sign of old blood and often happens at the beginning or end of a cycle. However, black menstrual blood can also be a sign of a vaginal blockage. Make sure to look out for symptoms such as itching, foul-smelling discharge, fever and difficulty peeing. If you have any of these symptoms, make sure to see a doctor or gynaecologist.

Bleeding between periods

Bleeding or spotting between periods can be expected when starting a new type of birth control. However, it can also be a sign of:

  • Pregnancy
  • Miscarriage
  • Ectopic pregnancy
  • An STI
  • Injury to the vagina
  • A recent abortion
  • Menopause
  • Polycystic ovarian syndrome
  • Endometriosis
  • Uterine fibroids
  • Cervical, vaginal or uterine cancer
  • Stress
  • Vaginal dryness
  • Emergency contraceptive side effects

If you are concerned about why you are spotting, then it is a good idea to seek the advice of a medical professional. You should also consult a doctor if:

  • You have new, unusual, grey or foul-smelling vaginal discharge
  • You have irregular periods
  • You experience bleeding after menopause
  • You miss three or more periods in a row
  • You have itching in or around the vagina
  • You experience burning during urination
  • You have a fever

Having a regular period is normal and a sign that your system is working; we should be proud of our periods. But we should also look out for when something isn’t quite right to ensure we stay healthy!

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