Why Do Hormones Cause Breast Discharge?

Hormones can cause normal breast discharge that’s related or unrelated to pregnancy. Common hormonal causes of nipple discharge include:

• Normal hormonal shifts (e.g., menstruation, pregnancy, breastfeeding, pregnancy loss)
• Hormonal medication side effects (e.g., birth control pills)
• Hormone-related health conditions (e.g., pituitary gland problems)

An unusual discharge from the nipple—for example, fluid that is milky or bloody—can be from a non-hormonal but possibly more serious cause, like an infection or breast cancer.

This article describes the different types of hormone-related nipple discharge, their symptoms, and what causes them. It also explains how to stop nipple discharge and what may be causing this if not hormonal changes.

Hormonal Breast Discharge Colors 

Nipple discharge can have different colors and consistencies. While typically thin and clear/white, it can also be:

• Yellow
• Green
• Brown
• Red

Or:

• Slightly thicker and milky
• Purulent (pus-like) and cloudy
• Very thick, sticky, and cheese-like

When hormones are the cause of nipple discharge, it’s usually milky-white in color. But this isn’t enough to confirm why it’s happening. That’s because there is some overlap among hormonal and non-hormonal causes, as well as conditions within each group.

For example, green breast discharge can occur because of hormonal shifts in pregnant and nursing people, but it can also be a sign of a breast infection.

Whether the discharge comes from one or both breasts can be a helpful clue:

Nipple discharge from both breasts is more likely to be related to hormonal changes or body-wide conditions, such as thyroid disease. Discharge from a single breast duct is less likely to have a hormonal cause.

The following may also be used to help differentiate hormonal from non-hormonal causes:

• Does the discharge have an odor?
• Does it occur spontaneously or only when the breast is pressed?
• What other symptoms are occurring? (e.g., a fever can be a sign of a breast infection, while missed periods can be a sign of pregnancy)
  

Nipple Discharge Hormonal Causes

Common hormonal causes of breast discharge include:

• Menstrual cycle changes (e.g., during premenopausal and postmenopausal periods of life)
  
• Pregnancy and lactation
• Galactorrhea
• Certain medical conditions that affect hormone levels
• Hormonal medications
  

Menstrual Cycle Changes

Normal fluctuations in estrogen levels throughout the menstrual cycle can lead to breast tissue changes and nipple discharge.

Some people get lumpy breasts (fibrocystic breasts), swelling, and tenderness during the premenstrual phase of their cycle and may have a little nipple discharge as well, especially when their breasts are touched. The discharge can be milky or green-brown.

Discharge can also occur as estrogen levels decrease as one approaches or reaches menopause.

Pregnancy and Breastfeeding

Colostrum (the fluid that comes in before breast milk) can start to leak weeks or even months before birth. It’s usually thin and light-yellow, then gets thicker and milky.

This discharge is a normal part of the body’s preparation for delivering and potentially breastfeeding an infant, so it’s not usually anything to worry about.

In newborns, small amounts of clear or milky nipple discharge are common. It may happen along with some breast swelling or a small lump. The condition is related to hormones left over from pregnancy.

Galactorrhea

Galactorrhea is a milky nipple discharge that happens when there are high levels of prolactin in the body (hyperprolactinemia). Prolactin is a hormone that is normally involved with breast growth and breastfeeding.

Higher-than-usual levels of this hormone can be caused by:

• Acid reflux drugs
• Antidepressants
• Antipsychotics
• Blood pressure drugs
• Dopamine antagonists
• Herbal supplements, (e.g., fenugreek, red clover, anise, and fennel)
• Opioids
• Sedatives
  

Medical Conditions Related to Hormones

Some health conditions can change the levels of certain hormones in your body.

Hypothyroidism (underactive thyroid) and non-cancerous growths on the pituitary gland can both cause nipple discharge because they can change how much prolactin is in your body.

Medications

Medications such as hormonal contraceptives (e.g., birth control pills) and hormone-replacement therapy (HRT) can have a milky nipple discharge as a side effect since they change the levels of hormones (like estrogen) in your body.

Non-Hormonal Causes of Breast Discharge

If you have breast discharge that’s not being caused by something hormonal, your provider may have to look for other possible causes.

Non-hormonal causes of breast discharge include:

• Blocked milk ducts (ectasia)
• Infections (e.g., mastitis)
• Non-cancerous growths (intraductal papilloma)
• Irritation (e.g., rough clothing or a poor-fitting bra, excess stimulation, trauma)
• Cancer (including Paget’s disease)

Mammary Duct Ectasia

Mammary duct ectasia is the medical term for blocked milk ducts. It's most common in people who are near menopause (perimenopause) or have gone through menopause. In this condition, the breast ducts widen and become clogged with thick discharge.

Nipple discharge from mammary duct ectasia can be:

• Clear to green, brown, or black
• Very thick and cheese-like
• Accompanied by red, tender nipples

The condition can lead to mastitis. When this happens, the nipples can turn inward (nipple inversion) and may make a person worry they could have breast cancer.  

Mammary duct ectasia usually goes away in time, but some cases require surgery. Hot packs can relieve discomfort from the condition.

Bloody discharge later in infancy can also be caused by mammary duct ectasia.

Infections

Mastitis is a breast infection that can cause symptoms such as:

• Pus-like yellow-green discharge
• Fever
• Pain
• Breast tenderness

If the nipple discharge is also foul-smelling, it could be coming from an abscess in the nipple or under the areola (the pigmented area around the nipple). An abscess is an area the body “walls off” to keep an infection from spreading. It’s a serious medical problem that needs treatment.

Intraductal Papillomas

Intraductal papillomas are non-cancerous (benign) growths that usually involve a single duct. they're most common during premenopause.

The growths often cause a clear or bloody discharge. You may also notice a painless lump on your nipple.

Most of these growths are not a concern, but some may have regions of papillary carcinoma of the breast—a precancerous condition called ductal carcinoma in situ (DCIS).

Breast Cancer

It’s rare, but nipple discharge is sometimes a sign of breast cancer. It can be an early warning sign of breast cancer that is still in the pre-invasive stage. This is more likely in someone over age 40 and/or if:

• The discharge is one-sided and spontaneous (without stimulation)
• The discharge comes from only one duct
• You have other symptoms of breast cancer (e.g., dimpling, retraction, nipple inversion, or a breast mass)

Nipple discharge from breast cancer can be bloody, clear, or milky.

Paget’s Disease

Paget’s disease of the breast is an uncommon form of breast cancer. It accounts for less than 3% of cases.

Paget’s disease causes: 

• Nipple discharge that’s often bloody
• Nipple tenderness or burning
• Redness, scaling, and/or flaking

It usually takes a biopsy to diagnose Paget’s disease. 

Diagnosis

Your provider will do some tests to figure out why you have nipple discharge. The specific tests they do will depend on your age, symptoms, and what is found during a physical exam. 

• Blood tests: Prolactin level and thyroid-stimulating hormone (TSH) tests are common.
• Brain MRI or CT scan: Magnetic resonance imaging (MRI) or computed tomography (CT) scans may be done to check for pituitary microadenoma.
• Cytology: A sample of discharge is collected and examined for cancer cells.
  
• Ultrasound: This imaging test looks for abnormalities behind the nipple and areola. It can identify papillomas, but a biopsy may also be needed.
• Ductogram: Dye is injected to evaluate breast milk to see if there are any blockages or growths.
• Biopsy: A breast biopsy is done to look at lumps near the nipple. A skin biopsy can help diagnose Paget's disease.

Treatment

When hormones are causing nipple discharge, it's typically part of a normal process in the body. For example, nipple discharge during pregnancy and breastfeeding is expected and does not need to be treated.

If you’re having nipple discharge because of a hormone-related disorder, managing that condition will probably make the symptom better. In the case of low thyroid, for example, Synthroid (levothyroxine) can replace the thyroid hormone you are lacking.

If you’re having nipple discharge as a medication side effect, you could ask your provider about switching to a different medication to see if it helps.

Non-hormonal causes are more likely to need treatment than hormonal causes of breast discharge simply because they are not usually part of a normal bodily process.

For example, a bacterial infection is usually treated with antibiotics. An intraductal papilloma that is causing symptoms can be surgically removed.

Summary

Any person with breasts can get nipple discharge, but it’s more likely to happen during hormonal times of life like menstruation, pregnancy, and menopause. During these times, some nipple discharge can actually be normal and not a reason to worry.

Hormone-related health problems and medications can also cause nipple discharge. You can work with your provider to manage the underlying condition or change your medications to see if it helps with the symptom.