Brown, black, bright red, pink: what period blood colour can and cannot tell you

You are looking at it right now, and it is not the colour you expected. Brown on the first day, something close to black on the last, pink on a liner in between. Nearly all of that variation comes down to two things: how long the blood took to leave, and how much it was diluted on the way out. Colour is one of the least informative things about a period. Timing, amount, smell and context tell a clinician far more, and this article is about which is which.

An open box of sanitary pads on a bathroom counter beside a sink. Photo by Karola G on Pexels.

Why blood changes colour at all

Blood is red because of haemoglobin, the protein in red blood cells that carries oxygen. Once blood leaves a vessel, haemoglobin starts to change. Forensic scientists study this closely because the colour of a bloodstain is used to estimate its age, and the sequence is well described: oxygen-bound haemoglobin is converted to methaemoglobin and then to a further breakdown product called hemichrome, and with each step the colour shifts from bright red towards dark red, brown and finally near-black. A review of this work in Forensic Science International sets out the chemistry in detail. The same process is happening inside you, only in the uterus and vagina rather than on a surface.

So the darkness of menstrual blood is mostly a clock. Blood that travels from the lining of the uterus to a pad in an hour looks fresh. Blood that pooled in the uterus overnight, or that trickled out slowly over a day of light flow, has had time to oxidise and looks older. Menstrual fluid also contains tissue from the uterine lining, cervical mucus and vaginal fluid, which is why it does not look or behave like blood from a cut, and why small amounts can look pink or watery once mixed with everything else.

The NHS puts it plainly in its overview of periods: at its heaviest the blood will be red, and on lighter days it may be pink or brown. That one sentence covers most of what you will ever see.

Reading the shades

Below is the same logic applied colour by colour. Treat it as a description of what you are looking at, not as a diagnosis of why.

Bright red. Flow is moving quickly, usually on the heaviest day or two. The NHS notes that bleeding tends to be heaviest in the first two days of a period, which is when bright red is most common. Bright red is not "healthier" than brown; it is just faster.

Dark red, burgundy, purplish. Slightly older blood, often on heavy days when a lot of it is leaving at once and some of it has sat for a while. Small clots are common in this range because blood that pools before leaving can clump. Clot size matters more than clot colour, and our guide to clots and heavy flow covers the thresholds ACOG and the NHS use.

Brown. Older still. Brown is typical at the very start of a period, when the first blood out has been waiting in the uterus, and at the end, when flow is slow enough that the blood oxidises before it reaches you. Brown spotting between periods is a different matter, not because of the colour but because of the timing, and spotting compared with a period explains how to tell them apart.

Black or near-black. The end of the same process. It is almost never literally black; it is brown so dark that it reads as black on a pad or in the toilet, and it turns up in the same places brown does, at the slow start and the slow tail of bleeding. If you sleep in, the first blood of the morning is often the darkest you will see all cycle, for the simple reason that it has been sitting for eight hours.

Pink. Usually a small amount of blood diluted by cervical mucus or vaginal fluid, which is why it appears on the lightest days, on liners, and around ovulation in people who spot mid-cycle. Hormonal contraception can also make bleeding lighter and paler by thinning the uterine lining, which is an expected effect of the method rather than a fault, as how birth control changes bleeding sets out.

Orange. Red blood mixed with a larger proportion of yellowish cervical fluid can look orange. On its own, at the start or end of a period, that is the likely explanation. Orange with an unpleasant smell, itching or soreness is a discharge question rather than a colour question, and is covered below.

Notice that none of these entries ends with a disease. That is deliberate. The colour of blood during a period is not something clinicians use to make a diagnosis. A Cleveland Clinic gynaecologist has said as much directly: the colour of period blood tells her very little, and the things she investigates are spotting between periods, bleeding after menopause, and flow that is unusually heavy or light. ACOG's guidance on abnormal uterine bleeding is built entirely around timing, duration and amount, and when it asks you to keep a record it asks for dates, length and how heavy the bleeding was. Colour is not on the list.

The short list that is worth attention

The exceptions are about context, not shade. A brown day in the middle of an otherwise ordinary period means nothing. The same brown discharge in a woman who has not had a period in two years is something the NHS wants seen within a fortnight. Here is where colour observations should send you to a clinician.

Grey, greenish or yellow discharge, or anything with a strong or fishy smell. These are signs of infection or an imbalance in the vaginal bacteria, not of ageing blood. The NHS describes bacterial vaginosis as producing a greyish-white, thin, watery discharge with a strong fishy smell, and lists green, yellow or frothy discharge among the changes that should be checked. It also notes that half of women with bacterial vaginosis have no symptoms at all, so a period that suddenly smells different is worth mentioning even if nothing else has changed. A sexual health clinic can test and treat this quickly.

Dark or foul-smelling discharge when something might have been left in. The Mayo Clinic lists a retained tampon among the causes of unusual vaginal bleeding, and it is a recognisable pattern: dark discharge, a bad smell, sometimes fever or pelvic pain. The NHS advice is simple. If you think a tampon is still in and cannot remove it, go to a GP or sexual health clinic and they will take it out.

Any bleeding after menopause, of any colour. The NHS is unusually blunt here. Menopause is usually diagnosed after 12 months without a period, and any bleeding after that point should be seen by a GP, even if it happened once, even if it is only pink or brown discharge, even if you are not sure it was blood. Most causes are benign, thinning of the vaginal or uterine lining and polyps being the commonest, but womb cancer is among the possibilities and is easier to treat when found early. In the UK you should be referred to a specialist within two weeks.

Bleeding between periods or after sex, whatever the shade. Both are on ACOG's list of abnormal uterine bleeding and on the NHS list of bleeding that needs checking by a doctor. The reasons range from contraception and cervical irritation to infection and, rarely, cancer, and none of them can be told apart by colour.

Any bleeding when you are or could be pregnant. The NHS notes that bleeding in miscarriage can be anything from light brownish discharge to heavy bright red blood with clots, which means colour cannot reassure you or alarm you here. Contact a GP, maternity team or NHS 111 for any bleeding in pregnancy. Seek urgent help for bleeding with persistent one-sided pain, shoulder tip pain, or feeling faint, which can indicate an ectopic pregnancy.

A period that has changed from your own normal. Much darker and heavier than usual, with large clots, or lasting well beyond seven days, is a flow question rather than a colour question, and heavy flow has its own thresholds for when to seek help.

Situations where dark blood is expected

Two life stages produce a lot of brown and black bleeding and a lot of unnecessary worry.

After childbirth, bleeding known as lochia is heavy and red at first, may become redder again when you breastfeed because feeding makes the uterus contract, and then, in the NHS description, gradually turns brownish and decreases over a few weeks before stopping. Slow, dark lochia towards the end is old blood leaving late.

In perimenopause, ovulation becomes irregular and the uterine lining can build up unevenly, so ACOG notes that skipped periods and bleeding that is lighter or heavier than before are common. The first bleed after a long gap is often dark, because the lining had been sitting longer. That is expected. What is not expected is bleeding once periods have fully stopped, and perimenopause and period changes draws that line in more detail.

What is actually worth recording

If colour tells clinicians little, there is no need to log it obsessively. What earns a place in a record is the information that lets you and a clinician answer one question: is this new for me?

The first and last day of each bleed, so length and duration are visible across months
How heavy each day was, in practical terms — product changes, leaks, waking to change
Bleeding outside your period, with the date, so spotting can be read against the whole cycle
The details that matter more than colour — an unusual smell, itching, soreness, or pelvic pain
Context — contraception, pregnancy possibility, and any recent change to either

Colour can go in a note if it is new for you or if it came with one of the changes above. A single dark day at the end of a period does not need to be written down at all.

Flowy logs flow as spotting, light, medium or heavy, records spotting colour as red or brown, and keeps a free-text note for anything else, in a private log you can export. It does not analyse colour, cannot detect infection, cannot tell a period from pregnancy bleeding or postmenopausal bleeding, and its estimates are not contraception. A photograph compared against a chart, in any app, cannot do those things either.

Frequently asked questions

Is black period blood a sign of something serious?

On its own, at the start or end of a period, no. It is blood that has oxidised because it left slowly. It becomes worth a conversation when it arrives with a bad smell, fever or pelvic pain, when you might have a retained tampon, when you are pregnant, or when you are past menopause.

Why is my period brown on the first day?

The first blood to leave has usually been sitting in the uterus while flow was still slow, so it has had time to darken. Once the flow picks up it typically turns red.

Does brown blood mean I have low oestrogen or a hormone problem?

There is no published guidance from ACOG, the NHS or the Mayo Clinic that uses blood colour to assess hormone levels, and claims that a shade of brown reveals a specific deficiency are not something you should pay for. Persistent changes in the timing or amount of bleeding are what a clinician would use to decide whether hormone testing is worthwhile.

Should I take a photo to show my doctor?

You can, but it will rarely change the assessment. Dates, duration, how heavy the bleeding was, and any symptoms alongside it are what will be asked about.

This article is for general education only. It is not a diagnosis or a substitute for care from a qualified healthcare professional.