What are the causes of left breast pain in women? We will address the many possible causes of pain in this region—both those due to breast issues and those that are not—but first: Make sure it isn’t your heart.

First Step—Make Sure It’s Not Your Heart!
While your left breast pain is most likely due to something else, the first question you need to ask yourself is if you could be having symptoms of a heart attack. Keep in mind that the symptoms of heart disease in women are often very different from those in men. Pain may be mild, feel like a burning pain, or may simply feel like breast pain. Due to the often vague and subtle symptoms, women are more likely to overlook the signs, and, as a result, die from a heart attack.

Everyone should be familiar with the symptoms of a heart attack which may include:1

Chest pain or pressure: A fourth to a third of people having a heart attack do not experience any chest pain or pressure
Pain in your neck, jaw, or left arm
Shortness of breath: Shortness of breath is common in women who are having a heart attack
Lightheadedness or passing out
A feeling that something just isn’t right or a sense of impending doom
Could You Be Having A Heart Attack? How To Tell, What To Do
What Is the Origin?
After making sure you don’t need to call 911, the first step in figuring out the source of left-sided breast pain is to decide whether your pain is originating in your breast or instead related to other structures above or beneath your breast.

Sometimes this can be hard to determine, and both breast and non-breast causes need to be considered. 

The location in which we sense pain does not necessarily tell us the location of a medical problem. Some of the nerves in our body are very specific. For example, a sensation on your fingertip can usually be located very precisely. Other nerves are not as specific. They alert you to the general area of your body affected by some process, but they don’t locate the precise area of pain as accurately. If you’re finding it difficult to know whether the pain you’re feeling is in your breasts rather than some other structure in the general vicinity of your left breast, you are not alone. 

Breast-Related Causes of Left-Sided Breast Pain

 Illustration by Emily Roberts, Verywell
We will take a look at possible breast-related causes of left-sided chest pain, and then discuss the chance that it may be cancer or due to a condition outside of the breast. Breast conditions which may cause left-sided breast pain alone may include:

Injuries: Your breasts are covered with sensitive, elastic skin that protects nerves, blood vessels, and connective tissues as well as ducts and lobes for producing breast milk. If you’ve had a breast injury, you can expect bruising and an ache that will persist until the skin and underlying tissues have healed. Sometimes an injury to the breast heals with scar tissue, and this scar tissue can cause pain (fat necrosis).2 Fat necrosis may appear as a hard lump as well, making it difficult to distinguish from breast cancer, even on imaging tests such as a mammogram.

Breast surgery: After any type of breast surgery whether it is an augmentation, reduction, or reconstruction—your breasts will hurt as incisions heal and scar tissue develops. And as with scar tissue related to an injury, pain can come and go even long after your surgery.

Milk duct conditions and infections: Several benign but painful conditions can develop inside your breast milk system. An abscess may occur under your nipple or areola. Milk ducts can become clogged and infected, causing mastitis (a breast infection)3 or ductal ectasia. Breast cysts and fibroadenomas may grow and crowd your milk system or connective tissue, creating aches and pains.

Hormonal causes: Hormone changes may also cause breast tenderness, especially when levels change during a woman’s menstrual cycle4 or while on hormones such as oral contraceptive pills, infertility treatments, or hormone replacement therapy. While hormonal changes often cause pain in both breasts, the pain may be felt in one breast more than the other. Hypothyroidism—characterized by a low level of thyroid hormones in the body—may also be linked to benign breast disorders that cause breast pain. 

Infection/Inflammation: If you suspect a breast infection (mastitis) or inflammation, it’s important to visit your family doctor or gynecologist. You may need to take antibiotics or other prescription medications to clear up the problem.

Lumps: Finally, whenever you find breast lumps or bumps that are not related to your menstrual cycle, or even if they are related to your menstrual cycle, consult with your doctor right away to get a clear diagnosis and proper treatment.5 While your doctor may be able to make a good guess as to whether a lump is benign or malignant, imaging tests and sometimes a biopsy is often needed to be sure.

Left Breast Pain Due to Left Sided Breast Cancer
Most of the time—but certainly not always—breast cancer is painless in the early stages. There are exceptions to this rule, especially with cancers such as inflammatory breast cancer.

Inflammatory breast cancer is an aggressive cancer form of breast cancer which usually begins with pain, redness, and swelling in the breast. Most people are unable to feel a discreet lump, and cancer often resembles an infection. Early on, the only symptom may be the pain in one breast or the other.

Breast cancer in women occurs slightly more often on the left side than the right, although it occurs equally on both sides in men. While in general, breast lumps due to cancer are painless, there are many exceptions. While breast pain is more likely to be due to something other than breast cancer, roughly one in six women with breast cancer have breast pain during the 90 day period prior to diagnosis.6

Non-Breast Related Causes of Left Breast Pain

 Illustration by Emily Roberts, Verywell
Sometimes when pain happens, it is hard to tell exactly what hurts and where the pain is centered. When pain hits you on the left side of your chest, you may think it is left breast pain, but the pain may actually be beneath your left breast. Some non-breast related causes of pain that feel like it is in your breast include:

Chest wall pain: Below your breast there are chest wall muscles that may spasm during times of anxiety and stress, causing pain that may last just a few seconds or several days. Pain from tense chest wall muscles can occur on the left side only, or on the right. Likewise, if you have a pulled chest muscle or an injury to the left chest, aches and pains may result.7

Cardiac causes: As noted above, the pain associated with heart attacks in women is often vague and different than the symptoms in men. If you are uncertain about the origin of your pain and have any risk factors for heart disease, it may be better to play on the safe side and seek immediate medical attention. While the typical symptoms of a heart attack include a squeezing pain or pressure in the chest area, accompanied by lightheadedness or sweating, some people—especially women—have only mild or atypical symptoms. These may include nausea and vomiting, feeling short of breath, or back or jaw pain.

Esophageal causes: Since your esophagus runs below your left breast, gastroesophageal reflux disease can occasionally feel like left breast pain.8 A related condition, hiatal hernia, may cause similar symptoms. Pain related to the esophagus may feel more like a burning pain, and you may have associated symptoms of an acidic taste in your mouth. But not always. Other digestive system conditions such as liver disease may also, at times, cause pain that feels like it is coming from your breast.

Cartilage: Inflammation of the cartilage between your breastbone (sternum) and your ribs, something called costochondritis, may cause pain on the right or left side of the chest.9 

Fibromyalgia: Fibromyalgia may cause pain anywhere in your body, and chest pain is not uncommon.10 Fibromyalgia can affect muscles, joints, and connective tissues, creating generalized pain or focused pain.

Pneumonia: Pneumonia can also cause left-sided pain since your lungs are in your chest area underneath your breasts.11

Pulmonary emboli: Blood clots in your legs that break off and travel to your lungs, pulmonary emboli, may cause pain that feels like it is coming from your breast.

Skin Related Causes such as Shingles
Sometimes women develop pain which feels like it is either in the skin or on the outer surface of the breast. This may be shingles, a condition caused by the reactivation of the chickenpox years or decades after the primary infection.12 The problem with shingles is that the pain may precede the onset of the rash by several days.

Shingles: A Late-in-life Complication of Chickenpox
What Should I Do If I Have Left Breast Pain?
There are a number of causes of left-sided breast pain, some more serious than others. The only way to know for sure is to seek medical attention. 

Whether your left breast pain is due to a minor nuisance condition or a larger problem such as breast cancer or even heart disease, it’s important to get an answer to the question of what is causing your pain. Pain is our body’s way of alerting us to a problem. 

If you’ve seen your doctor but still lack an adequate explanation for your pain, call again. You may need to consider getting a second opinion if the pain persists.

Finally, keep in mind that even with an explanation, it’s certainly not unheard of for a person to have more than one process being responsible for pain. For example, you may have a common breast condition such as a breast cyst along with the common condition costochondritis. In fact, it’s not uncommon for people to receive a diagnosis of cancer after an evaluation for a seemingly unrelated concern.