Watery period blood: What it means, causes & treatment

What is a normal period flow?

What’s ‘normal’ when it comes to periods? That’s the million-dollar question. It can feel like a lot of blood when you’re on your period, but it might surprise you to learn that it’s not as much as you may think. Most women lose between 20 and 90 ml of blood (0.7 to 3 fl oz), which is around one to five tablespoons, although everyone is different and some people may lose more blood — and others less [1]. Heavy bleeding is defined as losing more than 80ml (2.7 fl oz) of blood per cycle (equivalent to 5+ tablespoons), while light bleeding is typically losing less than 5ml (0.16 fl oz) per cycle (around 1 teaspoon) [2].

When it comes to period flow, it’s heaviest for most people in the first two days of their period, and periods usually last between two to seven days, but five is around average. After the first couple of days with a heavier flow, period flow often becomes lighter [1,3].

While you might think of period blood as being red, there are actually several different colors it can be, depending on the stage of your period, and whether there are any other health concerns. It can vary in color from dark brown to pink, and it may be thin or clumpy [4]. All of these can be considered “normal” – but it’s always important to know what’s normal for you, so you can spot whether there are any changes to your flow.

Is a watery period normal?

In most cases, yes, watery period blood is nothing to worry about. A period isn’t made up of pure blood – it’s actually a mixture of blood, endometrial tissue, and other secretions. Blood can make up anything from 1.6% to 81.7% of the total fluid, which means that some people’s periods are more watery than others [5]. The consistency can vary between cycles, and even from day to day within the same period.

But if you notice any changes in the consistency of your period, or have any other concerning symptoms, it’s worth speaking to your healthcare provider. Tracking your period can help you more easily notice any changes that occur.

Why is my period blood watery?

There are several reasons why your period blood might appear watery. In most cases, it's a normal variation or due to hormonal changes. Let's take a look at the most common causes.

Causes of watery period blood

1. Hormonal birth control

Hormonal birth control, including the pill, patch, vaginal ring, IUD, and implant, work primarily by preventing ovulation and thickening cervical mucus to block sperm. They also thin the uterine lining, which makes implantation even less likely in the rare event an egg is released and fertilized [6].

Because there’s less tissue mixed in with your menstrual fluid, it can mean your flow is lighter, which may appear more watery rather than thick. This is a normal side effect of some hormonal contraception and isn't usually a cause for concern [7]. If you've recently started a new form of birth control and notice your period has become watery, this may be the reason.

2. Perimenopause

In the lead-up to menopause, known as perimenopause, your hormone levels fluctuate as your ovaries begin to make less estrogen [8]. That can lead to common symptoms like hot flashes, difficulty sleeping, reduced sex drive, weight changes, and night sweats [9]. 

Another common symptom of perimenopause is changes to your menstrual cycle. You may experience longer or shorter periods, and your periods may be heavier or lighter than before. That’s because during perimenopause, the ovaries begin to make less estrogen – but it can be erratic, with the ovaries releasing an egg some months and not during other months. This can cause your uterine lining to build up irregularly, often leading to heavier or more unpredictable bleeding. However, some people also experience lighter periods, which may seem watery, and for some people, their periods may stop completely during perimenopause [8].

3. Low estrogen levels

The composition of your period can vary depending on your hormone levels, particularly estrogen. Estrogen is the primary hormone that’s responsible for building up the lining of the uterus during the menstrual cycle [10]. During the follicular phase of the menstrual cycle, rising estrogen levels increase, the uterine lining becomes filled with more blood vessels, and water accumulates between cells in the tissue [11]. When estrogen levels are low, though, the uterine lining doesn’t thicken as much [12]. That means there’s less tissue to shed during your period, which can make your flow seem lighter and more watery.

Once the majority of the uterine lining is shed in the first few days of a period bleed, the remaining days tend to be lighter and more watery. Low estrogen levels can also be caused by various other factors — if you’re concerned, it’s best to speak to your healthcare provider to find out more.

4. Increased vaginal discharge

If you have a lot of vaginal discharge, it can mix with your menstrual blood — and that may make your period seem watery. The amount of discharge naturally varies, and it may be heavier if you're sexually active or if you're using birth control. Healthy vaginal discharge is thick, slippery, and wet, clear or white in color, and doesn’t have a strong or unpleasant odor [13].

Some conditions can cause an increase in watery discharge, including bacterial vaginosis (BV). This common vaginal infection can cause thin, watery discharge with an unpleasant fishy-smelling odor [14]. If you have BV around the time of your period, the discharge can make your period seem more watery.

If you notice that your discharge is more watery than normal, has an unusual odor, or see any other changes in your discharge, it’s worth getting checked by your doctor or local sexual health clinic.

5. Weight changes

Whether it’s weight loss or gain, a change in weight can disrupt your normal hormone production and have an impact on both the flow and consistency of your period. Losing weight, in particular, can reduce your estrogen levels. One study that looked specifically at postmenopausal women who were in the obese or overweight category found that estrogen levels dropped significantly when weight was lost through diet and exercise [15].

Since estrogen helps build up the uterine lining, lower estrogen levels may result in a thinner lining, which could make your period appear lighter and more watery.

On the other hand, significant weight gain can also affect your hormonal balance and may lead to changes in your menstrual flow and consistency, and in some cases, heavier cycles [16].

6. Stress

If you’ve ever gone through a period of stress, you may have noticed that it had an impact on your period. Mental and emotional stress can disrupt the system that controls your reproductive hormones. And any sort of disruption to this system can have a knock-on effect on your menstrual cycle. Sometimes this means ovulation is delayed, and other times it doesn't happen at all, which is known as an anovulatory cycle [17].

Bodily stress (such as malnutrition, over-exercising, or being ill) can also disrupt your menstrual cycle, causing a delayed or even skipped period. Low weight, excessive exercise, or stress can lead to hormonal changes that result in functional hypothalamic amenorrhea, a menstrual disorder that can cause absent or very light periods [16]. 

Watery period blood vs. implantation bleeding

Another potential reason you may have light bleeding or spotting is implantation bleeding. This is a reported phenomenon, but little is known about it, and not everyone experiences it. More research is needed into how common implantation bleeding but it’s thought to occur around the time your period is due, which is why you may confuse implantation bleeding with watery period blood [18]. Implantation bleeding is reported to be very light bleeding, and shouldn’t be heavy enough to soak through your underwear or a pad [19].

Because implantation bleeding typically happens around the time your period would be expected, it can be difficult to tell the difference. If you suspect you might be pregnant, the most reliable way to know is to take a pregnancy test on the first day of your missed period. Remember to contact your healthcare provider if you have any concerns about bleeding.

Treatment options

Watery period blood itself doesn't usually require treatment. That’s because it’s either normal for you, or because it’s a symptom of an underlying condition, rather than a condition on its own. The approach to treating watery periods, then, depends on what’s causing them.

Your periods can change — for example, they may last longer or get lighter. This does not necessarily mean there's a problem, but if you notice a change in your periods, it’s a good idea to speak to your doctor. The NC° app can help you keep track of your cycle, helping you to understand what’s normal for you. Because Natural Cycles tracks ovulation, not just periods, meaning you can look for patterns and see whether changes in bleeding correlate with anovulatory cycles or late ovulation.

In many cases, if watery period blood is simply due to normal hormonal fluctuations, starting or stopping birth control, no specific treatment may be necessary. Although if the cause is lifestyle-related, e.g., caused by stress or weight changes, you may want to discuss those root causes with your doctor. 

When to see a doctor

Your periods can change from cycle to cycle, and during different phases of your life. They may last longer or get lighter. This doesn’t necessarily mean there's a problem, but it’s a good idea to investigate any significant changes.

You may wish to see a doctor if:

• Your periods have changed significantly: If your period suddenly becomes consistently watery over multiple cycles and this is unusual for you, it's worth getting it checked out.
• You experience other symptoms: Bleeding between periods, bleeding after having sex, or bleeding after the menopause needs to be checked by a doctor [1]. You should also seek medical advice if you have unusual vaginal discharge, particularly if it has an unpleasant odor or is accompanied by itching or pain [13].
• You have heavy periods: If your period is heavy and affecting your day-to-day life, or if you have heavy periods along with other symptoms (like pain during sex), then it’s a good idea to speak to your healthcare provider [20].

While watery period blood is usually nothing to worry about, it’s always worth consulting a professional if you have any concerns. They can help you understand what's normal for your body, rule out any underlying conditions, and address any questions you may have about your menstrual health.

Get to know your normal

Watery periods may be completely normal for you — or they may be a sign that there’s something else going on that needs investigating. That’s why it’s important to know what’s typical for you. With Natural Cycles, you can track not just your periods but your whole cycle, including ovulation. This empowers you to record symptoms and notice patterns; you can even download your Cycle Report as a handy PDF to share with your doctor. In addition, Natural Cycles is FDA-cleared for use as contraception and to plan pregnancy, supporting you on your fertility journey. Find out if it could work for you today!