Sore Nipples and Hormone Imbalance

  • 1st Revision: Isobel Lester
  • 2nd Revision: Alex Jasnosz
  • 3rd Revision: Tricia Li

Short Explainer Video

Statistics show that 70% of people assigned female at birth (AFAB) have experienced breast pain or sore nipples at some point in their lives.1

Although we commonly associate breast pain to be an issue exclusively affecting cis-gender women, it is important to remember that breast tissue pain and nipple soreness are a common side effect of hormone replacement therapy.

What is breast pain?

Breast pain (also called mastalgia) is characterized by throbbing, sharp, burning pain or tightness and/or tenderness in the breast tissue and/or the nipples.2

Breast pain can last for several days or just mere minutes; it can be a constant pain or an occasional experience.

Types of breast pain and what causes it?

A common way to categorize different types of breast pain is to see whether it is cyclic or non-cyclic. 

Cyclic breast pain is usually defined by the following symptoms:

  • Pain occurs on a regular basis, for example every month before your period (usually 1 to 2 weeks before the period) and eases up after the bleeding ends.
  • In addition to breast pain, you might also experience breast swelling, fullness or lumpiness.
  • The pain usually affects the upper, outer portions of the breast and may radiate to the underarm.

However, it should be noted that the exact cause of the cyclic breast pain remains unclear. The only thing we know for sure is that although hormones play a vital role in period-related cyclic breast pain, they are not the only reason.

Non-cyclic breast pain is usually defined by the following symptoms:

  • The occurrence of the pain is not related to your menstrual cycle.
  • The pain usually affects only one breast.

There are various factors that may lead to you having sore nipples and discomfort in your breasts.

A common cause for cyclic breast pain is hormonal fluctuation before a period starts, while for non-cyclic breast pain, causes include infections or simply wearing tight clothing.

In this article, we will further discuss some common causes of breast pain.1

Hormonal fluctuations

Hormonal fluctuation is the most common cause of cyclic breast pain and its occurrence is closely related to your menstrual cycle.2

What happens before your period?

Every month, one of several egg cells will mature in your ovaries and wait for a sperm cell to fertilise them. Meanwhile, your body is also preparing you for pregnancy in case an egg meets a sperm. 

What does a fetus need and how should our body prepare for it?

For a fetus to grow in the uterus, the uterine lining needs to thicken so that it can offer the fetus more support and protection. Additionally, breasts need to grow larger with more glands so that the potential baby will get enough milk. 

The role of oestrogen

To fulfill all these needs, the body releases a hormone called oestrogen, which thickens the uterine lining and leads to the growth of glands in breasts.

As a result, some menstruating people will experience swelling and pain in their breasts as the glands are stimulated to grow.

The role of progesterone

Another hormone involved is progesterone, which leads to swelling of milk ducts in the second half of your cycle. Milk ducts increasing in both number and size lead to breast pain right before the bleeding part of your cycle.

Some may be wondering: since every menstruating person has increased oestrogen levels before their period, why doesn’t every menstruating person experience breast pain?

This is because for each person, the sensitivity of their body to oestrogen stimulation is different. 

Usually, hormone fluctuations tend to affect both breasts, however, some menstruating people experience soreness in only one breast before their period. And even though we call this “cyclic breast pain”, it does not mean that a person with this condition will definitely experience discomfort in their breasts every month before their period. 

Lifestyle factors

Other lifestyle factors such as diet, stress and exercise co-affect hormonal fluctuations —this is why many menstruating people will experience breast pain in some months, but not the other.3

Furthermore, hormone fluctuations are also related to pregnancy. Breast pain is a very common sign of early pregnancy, especially in the first trimester.

As mentioned before, hormones are flooding the body to sustain development of the baby in the uterus and to stimulate breast growth.4

As early stages of pregnancy lead to release of higher than during a menstrual cycle amounts of oestrogen, pregnant women can experience more severe pain and sensitivity in their breasts.

Diseases that lead to breast pain

Hormonal reasons leading to breast pain are not something to be too worried about —it is part of the normal physiological process. What we should be concerned about are the diseases that lead to breast pain.

  • Mastitis

Mastitis happens when bacteria grow inside blocked milk ducts, leading to infection. Although women can have this condition anytime in their life, it usually happens during breastfeeding.

In addition to breast pain, it is accompanied by other symptoms such as: fever, warmth or burning in the breast and swelling of a part or a whole breast.

  • Thrush

Thrush is an infection of the breast and nipple caused by yeast. It can happen when you are breastfeeding, especially if you have cracks in your nipple.

The accompanying symptoms include redness of nipples and/or breasts, and dry or flaky skin around the nipple.

  • Breast cancer

Although breast pain is one of the easiest to notice symptoms of breast cancer, it is likely to be accompanied by one or more of the following:4

  • A nipple that turns inwards
  • Redness or scaling of the skin over the breast or nipple
  • Abnormal discharge from the nipple (not breast milk)
  • Swollen lymph nodes under your arm.

Other causes of breast pain

  • Clothes that do not fit you

If a bra or clothes are too loose to fit, it is possible they will rub against your nipple, especially when you are jumping or running. The friction may even cause the nipples to bleed.

If the clothes or the bra are too tight, then they might reduce the blood flowing to your underarm and breasts, leading to discomfort and even pain.

  • Skin Irritation

Allergies and irritants in your environment (for example your soap or laundry detergent) can cause skin irritation and discomfort in your breasts.

  • Iodine Deficiency

Second to thyroid, ovaries and breast tissue store higher amounts of iodine than anywhere else in the body. One of the main roles of iodine is making cells less sensitive to oestrogen.

If you are iodine deficient, you are also likely to be more sensitive to oestrogen, especially when its levels increase before the second half of your cycle. This increased sensitivity to oestrogen leads then to breast pain.5

Therefore, it is recommended that you take in enough iodine from your diet. You can choose iodized salt when cooking and iodine can also be found in foods such as:

  • Fish (such as cod and tuna)
  • Seaweed
  • Shrimp
  • Dairy products


To summarize, breast pain is something that many will encounter throughout their lives. In most cases, it is nothing to worry about, however it is always good to understand the possible causes. So if a clinical condition were to appear, you would know what other symptoms to look for.


  1. Goyal A. Breast pain [Internet]. PubMed Central (PMC). 2021 [cited 12 December 2021]. Available from:
  2. MT T, S S. Mastalgia [Internet]. PubMed. 2021 [cited 12 December 2021]. Available from:
  3. Breast Pain (Mastalgia) - Health Encyclopedia - University of Rochester Medical Center [Internet]. 2021 [cited 12 December 2021]. Available from:
  4. Koo M, von Wagner C, Abel G, McPhail S, Rubin G, Lyratzopoulos G. Typical and atypical presenting symptoms of breast cancer and their associations with diagnostic intervals: Evidence from a national audit of cancer diagnosis. Cancer Epidemiology. 2017;48:140-146.
  5. Office of Dietary Supplements - Iodine [Internet]. 2021 [cited 12 December 2021]. Available from:
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Adina Zhao

Medical Bioscientist - Imperial College London Medical Bioscience BSc
Modules covered: Integrative Body Systems, Molecular and Cellular Biology, Chemistry of Biological Interactions.
Past projects: Investigation of the influence of amino acid mutations of in-cluster gene lmbU on LmbU protein transcription and translation efficiency in Streptomyces lincolnensis, Investigation of the influence of red fluorescence protein mCherry on the photosynthetic efficiency of Arabidopsis thaliana .

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