A common cause of breast pain is pregnancy. As a fetus grows in its mother’s uterus (womb), her body prepares itself for delivery.

During this time, the milk glands swell in preparation for milk production. The rising hormone levels result in increased blood flow to the breast and lead to breast tissue changes that cause the breasts to feel swollen, sore and tender. This swelling may cause breasts to feel lumpier than normal, which can result in pain or discomfort in some women. Women should inform their physician of any lumps that develop within the breast during pregnancy. Although a lump may result from a clogged milk duct, it can indicate the presence of breast cancer in rare instances.

Breastfeeding is also a common cause of breast pain in many women. When milk ducts become blocked, milk accumulates in the breast, causing intense pain and discomfort in one or both breasts. The blockage, in turn, often leads to a bacterial infection known as mastitis. This condition, which makes the breast appear red and become warm, tender and possibly lumpy, occurs most often in women who are breastfeeding.

Many women who develop mastitis also report flu-like symptoms, including chills, a fever and fatigue. This is often a sign that the clogged duct has become infected. Mastitis can also occur in nonlactating, older women. This condition, known as periductal mastitis, develops when the milk ducts in the nipple become painfully inflamed. Any suspicion of a clogged milk duct and resulting breast infection should be evaluated by a physician since a certain type of breast cancer known as inflammatory breast cancer can be confused with mastitis.

When mastitis is detected early, it can be cured with antibiotics. When it is found later, after pus-containing abscesses have formed, the abscesses must be drained or surgically removed.

It is also common for new, breastfeeding mothers to report sore nipples. However, severe or prolonged pain is not normal and should be reported to the physician. Other conditions that may cause pain while breastfeeding include:

• Engorgement (the breast becomes overfilled with milk). When combined with the additional blood supply to the breast, engorgement can cause pain and swelling of the tissue that surrounds the nipple. Although not every new mother will develop engorgement, it is not uncommon for breasts to feel swollen, tender, throbbing, lumpy and uncomfortably full about two to three days after giving birth. However, most lactation experts believe that engorgement is preventable by breastfeeding early and frequently.
  
  
• Rashes. When breastfeeding, it is not uncommon for a woman to have dry, cracked or itchy rashes, even eczema, on the breast or nipples. These symptoms can cause varying levels of pain for a woman.
  
  
• Breast herpes. Women who have been exposed to the herpes simplex virus (HSV) can develop painful sores on their nipples that may be more prominent while breastfeeding. In such cases, the breast milk will need to be expressed, possibly using a breast pump, and given to the baby through a bottle until the virus has vanished.
  

• Infections. There are several types of infections that can occur in the breast.  It is possible for yeast or bacteria to infiltrate the nipple during breastfeeding. This can lead to impetigo (a bacterial infection) or thrush (a yeast infection) of the nipple characterized by deep, shooting breast pains, burning or irritation after feedings.
  
  A bleb is another infection that can occur in the breast. Although highly uncommon, a whitish, tender area can appear under the areola during breastfeeding. This area appears to have milk trapped just beneath the skin, causing the nipple and areola to become inflamed.
  
  

  Chronic subareolar abscess is a rare bacterial infection that occurs within the sebaceous glands around the nipples. The result is blocked glands that lead to redness or even painful boils. 
  

• Producing too much milk (hyperlactation).
  
  
• Strained chest muscles.
  
  
• Injury to the breast during childbirth.

In addition, breast pain may result from improper breast pump usage, an ill-fitting nursing bra or uncomfortable positioning during nursing.