The National Cancer Institute describes how the breasts are composed of three types of tissue: fatty, glandular and connective. Both connective and glandular tissue are quite dense and appear white on a mammogram. Fatty tissue is much less dense and appears black on a mammogram. Other components of the breasts include lobes, lobules and ducts, which are involved in the milk-producing function of the breast. These components can become "lumpy" due to multiple disorders and normal bodily changes.
Menstrual Periods
During or before a woman's menstrual periods, breasts often become tender, swollen or even painful. During this time, extra fluid builds up in the breasts, which may cause one, two or more lumps, according to the National Cancer Institute. The fluid retention and lumps typically resolve by the end of the menstrual period.
Pregnancy
Pregnancy is also a cause of lumps in the breast. Most often, this is due to normal growth of milk glands, which are growing in preparation for breast feeding.
Mastitis
According to the National Cancer Institute, mastitis can cause a lump in the breast, and occurs during breastfeeding. Occasionally the duct that produces milk can become blocked, causing the breast to look red and a lump to appear. Mastitis is most common while a woman is breast feeding, but Merck Manuals, an online medical library, reports that it sometimes occurs after injury to the breast or after breast surgery. When mastitis is caused by an infection, it can be treated with antibiotics.
Fibroadenomas
Merck Manuals cites fibroadenoma as another cause of breast lumps. This type of lump most often develops in young women and adolescents. The lump is usually painless and feels like smooth, slippery marbles. Fibroadenomas are not cancerous and do not increase the likelihood that cancer may develop later in life.
Galactocele
Galactocele is a cyst filled with breast milk that can develop in a woman approximately 6 to 10 months after ceasing breastfeeding, according to Merck Manuals. Galactocele is generally round in shape and can be easily moved within the breast. This type of cyst usually does not become infected.
Hormone Changes
Both girls and boys can develop lumps in their breasts due to changes in hormone levels in the body, according to MedlinePlus, an online medical encyclopedia sponsored by the U.S. National Library of Medicine. Babies can develop lumps in their breasts caused by ingesting their mother's estrogen through breast milk. Usually at around age 9, girls develop lumps that mark the beginning of growing breasts; these lumps are called "breast buds." In the middle of puberty, teenage boys can develop breasts and/or breast lumps due to hormonal changes.
Cancer
MedlinePlus reports that cancer can also cause breast lumps, though breast lumps are more commonly due to other causes. Breast cancer occurs when cells of the breast transform into a new type of cell that grows rapidly, does not die when it should and damages the normal tissue around it.
