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Overview

What Is Accessory Breast Tissue?

Accessory breast tissue is extra breast tissue that develops along the embryonic milk line, which runs from the armpit toward the groin. It most commonly appears near the armpit and may occur with or without a nipple or areola. It is usually present from birth, but it may not become noticeable until puberty, pregnancy, breastfeeding, or another time of hormonal change. This tissue is sometimes called axillary breast tissue, and its appearance does not mean someone literally has “three breasts.”

Symptoms

Symptoms of Accessory Breast Tissue

  • A lump or fullness near the armpit.
  • Swelling that varies with the menstrual cycle.
  • Tenderness that varies with the menstrual cycle.
  • Enlargement during pregnancy or breastfeeding.
  • Milk production from an accessory nipple.
  • Skin irritation where tissue rubs against clothing or the upper arm.

When symptoms need attention

Check new underarm lumps

An accessory nipple may look like a mole or skin tag, while accessory breast tissue may feel like a soft or firm lump. Arrange an evaluation for a new, hard, fixed, rapidly growing, or persistent lump rather than assuming it is breast tissue under the armpit.

Causes

What Causes Accessory Breast Tissue?

Accessory breast tissue forms when part of the embryonic milk line does not fully disappear during development. This is a congenital developmental difference, not something caused by an individual’s diet, exercise, or routine behavior.

Why It May Become Noticeable Later

During puberty, pregnancy, menstruation, or breastfeeding, hormones can stimulate the tissue and make it swell, feel tender, or become easier to see. Accessory breast may include a nipple and areola, or it may consist only of glandular or fatty tissue, especially near the armpit.

Risk Factors

Risk Factors for Accessory Breast Tissue

  • Congenital development is the main established factor because the tissue forms before birth.
  • A family history of similar tissue may be associated with its occurrence, although this does not prove a direct inherited cause.
  • Puberty can make previously unnoticed tissue more visible or tender.
  • Pregnancy can enlarge accessory breast tissue as breast tissue responds to hormones.
  • Breastfeeding may increase swelling or cause milk production in tissue connected to an accessory nipple.
  • Menstrual and other hormonal changes can make existing tissue fluctuate in size or tenderness.

Complications

Possible Complications

  • Cyclical pain or swelling.
  • Discomfort from friction or pressure.
  • Milk leakage or engorgement during lactation.
  • Benign breast conditions, such as cysts or other noncancerous changes.
  • Rare breast cancer arising in accessory tissue.

Cancer concern

Know concerning changes

Cancer in accessory breast tissue is uncommon, but it should be considered when a lump is new, persistent, enlarging, or firm. Skin changes or enlarged nearby lymph nodes also warrant medical assessment.

Diagnosis

How Accessory Breast Tissue Is Diagnosed

A clinician examines the location, texture, and size of the tissue and checks whether it is connected to a nipple or areola. They may ask whether it changes with menstrual cycles, pregnancy, or breastfeeding and compare it with the opposite side. The examination also helps distinguish axillary breast tissue from lymph nodes, a lipoma, a cyst, or another type of mass.

IMAGING

Ultrasound can characterize tissue in the armpit or breast and help identify breast-like tissue or another mass. Mammography may be used when appropriate for a person’s age and risk, while MRI is reserved for selected cases where findings remain unclear.

BIOPSY

A needle biopsy may be recommended when examination or imaging shows a suspicious lump, or when the diagnosis remains uncertain. It provides a tissue sample for laboratory review.

Treatment & Management

Treatment and Management

Asymptomatic accessory breast tissue that has been confidently diagnosed may only need observation and routine breast awareness. Supportive clothing can reduce movement and pressure, while reducing friction and using clinician-guided symptom relief may help with discomfort. Report changes in the tissue just as you would changes in the usual breast.

Procedural Options

Treatment decision

Removal is individualized

Surgical excision may be considered for persistent pain, repeated swelling, skin irritation, functional or cosmetic concerns, difficulty with breastfeeding, growth, or an uncertain diagnosis. For selected fatty or localized tissue, liposuction-based contouring may be an option. The approach depends on tissue type, nipple or areola involvement, symptoms, cosmetic goals, and cancer concern; discuss possible scarring, recurrence, sensation changes, and other procedure risks beforehand.

Outlook and Prognosis

Outlook for Accessory Breast Tissue

Accessory breast tissue is usually benign and does not necessarily cause ongoing problems. It may enlarge or become tender during hormonal changes, remain stable, shrink after pregnancy or breastfeeding, or persist long term. The course varies from person to person.

When Should You See a Doctor

When Should You See a Doctor?

  • A new or unexplained lump.
  • Rapid enlargement of the tissue.
  • Persistent pain.
  • Redness or other skin changes.
  • Nipple discharge or bleeding.
  • A hard or fixed mass.
  • Swollen lymph nodes near the area.
  • Symptoms that do not settle after pregnancy or breastfeeding.

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