Introduction

What is nipple discharge?

Nipple discharge occurs when fluid-like discharge leaks from your nipples. The fluid can vary in colour and texture, and these differences can help give important clues about what it may be and what might be causing it. It is the third most common reason why people visit the breast clinic. While the majority of nipple discharge cases are not serious and are usually harmless, it is essential to get it checked out since 5-12% of cases are linked to something more serious, like breast cancer.¹ 

Normal vs abnormal discharge

Normal nipple discharge 

• Common during pregnancy, breastfeeding, or hormonal changes
• It may be white, milky, clear, or yellowish
• It affects 50-70% of women, especially those who use pumps or with breast massages
• Known as physiological discharge, usually harmless

Abnormal nipple discharge

• Bloody or pink discharge, especially if it is spontaneous (no squeezing)
• Not related to pregnancy or breastfeeding
• Often benign, but should be checked
• Unilateral discharge (from one nipple only) may be a sign of an underlying issue² 

Importance of examination

• Nipple discharge of any kind should be consulted with a doctor to rule out serious causes 
• Each breast has 15-20 milk ducts, and discharge can come from one or more ducts 
• Most cases are harmless, but it is better to be safe 
• With the growing awareness of breast cancer, especially in women, more people are talking to their doctors about nipple discharge
• Discharge is normal during pregnancy and breastfeeding, during the last few weeks of pregnancy and after birth. Women who are not pregnant, during their reproductive years, can also have nipple discharge 
• Stimulation (e.g. touching or massaging) and stress can cause discharge 
• Postmenopausal women and men with nipple discharge should always seek further evaluation since it is not considered normal at that stage, and often signals something that needs to be looked into closely³ 

Clear nipple discharge

Characteristics

• Thin and watery
• See-through or slightly cloudy

Possible causes

Hormonal changes — Can occur as a normal response to changes during puberty or menopause.

Dust ectasia — Occurs when the milk ducts located under your nipple get wider and their walls thicken, which can cause blockages or fluid buildup. It is more common in women approaching or past menopause. The exact cause is not fully understood, but it is thought to be related to ageing and changes in the tissue around the ducts.⁴

Pregnancy and breastfeeding — Clear discharge during pregnancy is a normal occurrence as your body starts to make colostrum (first milk). This can lead to discharge before and after you give birth. In rare circumstances, this can continue for 2 years after stopping breastfeeding.⁵

Intraductal papilloma — Is a benign tumour that grows inside milk ducts, it is more prevalent in women over 40.⁶ 

Breast cancer (rare) — Although uncommon, is clear or bloody discharge from just one nipple may be a warning sign. Fewer than 5% of women with breast cancer experience nipple discharge, but it is still something to look out for.² 

When to look deeper?

Doctors will want to know whether the discharge happens on its own (spontaneously) or only when the nipple is squeezed, and whether it is coming from one breast (unilateral) or both (bilateral). If it is coming from just one breast and is persistent, tests like an ultrasound or a mammogram are usually performed to rule out serious causes..

Milky nipple discharge 

Characteristics

• Creamy and white, like milk 
• Varies in consistency — can be thick, thin, watery, or even sticky

Possible causes

Prolactinoma is a benign tumour in the pituitary gland that results in your body overproducing a hormone known as prolactin. This often leads to a milky nipple discharge. This condition is known as galactorrhea, which is an excess production of milk unrelated to pregnancy or breastfeeding.⁷ 

Medications Some medications, like antidepressants and birth control, can also trigger milky nipple discharge. This happens because birth control contains hormones like estrogen, which can dysregulate your body’s natural hormone balance.

Hypothyroidism is an underactive thyroid; it can cause your body to produce more prolactin than usual, which might lead to unexpected milky discharge. This can occur if you are not pregnant or breastfeeding.⁸ 

Chronic stimulation — Constant friction or rubbing, sometimes even from just clothing, can sometimes cause your breasts to release a milky nipple discharge. 

Evaluation

Doctors usually start by testing your hormone levels, especially for prolactin and thyroid hormones, via a blood test to rule out hyperprolactinemia (high prolactin in your blood) and hypothyroidism. Further investigation for hyperprolactinemia is a MRI to rule out serious causes.⁹  

Bloody nipple discharge

Characteristics

• Discharge can vary in colour, from bright red to dark

Possible causes

Intraductal papilloma: A benign breast tumour that develops inside the milk ducts and is a common cause of bloody nipple discharge.¹⁰ 

Ductal carcinoma in situ (DCIS): Is an invasive breast cancer found within the milk ducts of the breast. 

Many people with DCIS have no symptoms, but bloody nipple discharge can be a symptom. In a study, it was shown that 12.5% of women with bloody or discoloured nipple discharge were diagnosed with DCIS; most of them required further treatment, including surgery, even when imaging tests did not show anything abnormal. This highlights the importance of why unexplained bloody nipple discharge should always be taken seriously and investigated properly.¹¹ 

Trauma and post-surgical changes: Any kind of trauma or injury to the breast or nipple, following surgery, can also cause bloody discharge. It is usually harmless, but it is important to consult with a doctor..

Urgency and diagnostic workup

Bloody nipple discharge is usually considered abnormal and should always be further investigated. Even if imaging tests such as mammograms or ultrasounds do not show anything unusual, further testing should be undertaken. 

One useful tool is ductoscopy, which is a procedure which allows a tiny camera to be inserted into the milk ducts to look for any abnormalities. A study of 215 patients found that ductoscopy helped identify the cause of bloody nipple discharge, preventing them from needing any unnecessary surgery. It is a safe, well-tolerated, and helpful tool to use when other tests are inconclusive.¹² If anything suspicious is found on imaging tests, a biopsy is most likely to be recommended to check for cancer or any other causes.

Green nipple discharge

Characteristics

• Green or greenish-brown colour 
• Texture that can range from thin to sticky

Possible causes

Duct ectasia: Is a benign breast condition which causes milk ducts to widen and thicken, which can lead to green discharge.

Infections (mastitis): If the green discharge is associated with pain, swelling, or redness, this is usually an indication of infection of the breast. It is also referred to as mastitis, which is the inflammation of breast tissue. 

Clinical approach

Your doctor will examine the breast and nipple for any unusual abnormalities, such as lumps or signs of infection. Imaging tests may also be required to help rule out anything serious.

Purulent (Pus-like) nipple discharge

Characteristics

• Thick, cloudy, yellowish fluid
• May present with a bad smell
• It may be associated with pain, redness, or swelling

Possible causes

Breast abscess: Are infection in the breast tissue, which is often caused by bacteria. They can form painful, pus-filled lumps and can lead to nipple discharge. This occurs when milk ducts become blocked or inflamed and can leak into nearby tissues, which can cause abscesses ^{13, 14} Pus-like nipple discharge can also be a sign of mastitis, another breast infection.

Post-piercing infection: If piercings are not cared for properly, nipple piercings can lead to infections. This may result in pus-like discharge, swelling, and tenderness. In rare cases, certain bacteria like staphylococcus aureus or mycobacterium fortuitum (from water-contaminated equipment) can cause deeper or slow-developing infections. Toxic shock syndrome is also a high-risk risk serious condition that can develop.^15,16

Management

Treatment often involves antibiotics to manage infections, and in some cases, draining the abscess might be necessary.¹⁶  

Summary

• Nipple discharge can vary in appearance depending on the cause
• While nipple discharges are often harmless, they can sometimes be a sign of a more serious underlying condition such as cancer
• Recognising the type of discharge (clear, milky, bloody, green, or purulent) can help guide the diagnosis and treatment
• Most cases are not serious, but if symptoms persist and are associated with other features such as spontaneous discharge, bloody, unilateral leakage and or lumps and skin changes, it is important to consult a doctor