Breast swelling, often described as a feeling of fullness, tenderness, or engorgement, is a common physical symptom. It can range from mild, temporary discomfort to a more pronounced, painful condition. Understanding the underlying cause typically involves classifying the swelling based on whether it is generalized or localized, and if it follows a cyclical pattern. Most causes of breast swelling are benign and related to normal biological processes.
Swelling Related to Hormonal Cycles
Hormonal fluctuations are the most frequent cause of breast swelling, resulting in diffuse and often bilateral changes. These cyclical changes are directly driven by the sex hormones estrogen and progesterone. Estrogen stimulates the growth of the milk ducts, while progesterone promotes the development and swelling of the milk glands, or lobules.
This process results in premenstrual swelling, commonly known as cyclical mastalgia, where the breasts feel full, heavy, and tender in the week leading up to menstruation. Rising hormone levels cause fluid retention within the breast tissue, contributing to increased volume and density. Symptoms typically peak just before the menstrual period begins and then rapidly subside once the cycle starts.
Hormonal influence also causes swelling during other life stages. Puberty involves breast development known as thelarche, which can be accompanied by temporary tenderness or swelling. During pregnancy, sustained, high levels of estrogen and progesterone lead to rapid breast growth and engorgement as the milk-producing system matures. Postmenopausal individuals taking Hormone Replacement Therapy (HRT) may re-experience cyclical swelling and tenderness because the medication reintroduces hormonal stimulus to the breast tissue.
Swelling Caused by Infection and Acute Inflammation
Acute breast swelling that is localized often signals infection or inflammation, a condition known as mastitis. This is most common in breastfeeding individuals (lactational mastitis) due to milk stasis and bacterial entry through cracked nipples or duct openings. The trapped milk provides a medium for bacteria to multiply, triggering an immune response.
This type of swelling typically presents as a localized area that is hot, reddened, painful, and firm to the touch. Systemic symptoms, such as fever and general malaise, frequently accompany the inflammation. Non-lactational mastitis can also occur in non-breastfeeding women, sometimes linked to blocked and inflamed ducts (periductal mastitis) or due to skin wounds that introduce bacteria. If an acute infection is left untreated, it can progress to form a breast abscess, a painful collection of pus requiring drainage.
Structural Causes and Non-Infectious Masses
Localized swelling can arise from specific anatomical structures or benign growths. Fibrocystic changes, a common condition, often manifest as a lumpy or “ropy” texture in the breast tissue. These changes involve the development of fluid-filled sacs called simple cysts and an overgrowth of fibrous tissue (fibrosis).
Their size and associated tenderness often fluctuate with the menstrual cycle, as hormones cause the cysts to enlarge and become more noticeable before a period. Fibroadenomas are common benign masses: solid, rubbery, movable lumps composed of glandular and fibrous tissue. The tissue surrounding them may swell slightly in response to hormonal changes. Localized swelling can also result from direct injury to the chest wall or breast tissue, which can lead to a hematoma (a collection of clotted blood) that presents as a firm, tender, and potentially discolored lump.
Medications and External Factors
Certain medications can cause breast swelling by disrupting the body’s hormonal balance or by affecting fluid retention. Hormone therapies, such as oral contraceptives and hormone replacement therapy, can lead to breast fullness and tenderness due to the direct introduction of estrogens and progestins.
Some prescription drugs, including specific psychiatric medications and certain blood pressure treatments, can also cause breast changes. These may increase prolactin levels, a hormone that stimulates breast tissue, or interfere with the balance between estrogen and testosterone. External factors can also contribute to swelling; for instance, significant weight gain increases the amount of adipose tissue in the breast, leading to a noticeable increase in volume.