Lumps can occur in the left or right breast, or in both breasts. There are many types of breast lumps, most of which are harmless.

Doctors diagnose breast cancers more often in the left breast than the right. That said, around 80% of breast lumps turn out to be noncancerous. A breast lump may appear near the surface of the skin, deeper inside the breast tissue, or closer to the armpit area. People should see their doctor for any changes or lumps they find in their breast. This article looks at what breast lumps might mean and the different types that can occur. We also discuss how to check for lumps and when to see a doctor.

What to do if you find a lump in your left breast

If someone finds a lump in the left breast, they should remain calm. The first step is to work out the characteristics of the lump and look for any other breast changes. Breast tissue is naturally lumpy, and its textures change with hormones and aging processes. Compare the size, appearance, and texture of both breasts. Evenly dispersed lumps in both breasts usually indicate normal, healthy breast tissue. Lumps that differ from the surrounding breast tissue may suggest a tumor, which could be cancerous or noncancerous, or another breast condition.

The signs of breast cancer are different for different women. The most common signs are changes in the look or feel of the breast or nipple and nipple discharge. Look out for the following warning signs of breast cancer:

• A lump that has a different appearance or texture compared with the rest of the breast
• A lump that is hard or painful
• Dimpling or puckering of the skin
• A change in the size or shape of the breast
• Swelling, warmth, redness, or dark patches on the breast

The sections below discuss several types of breast lump and how to identify them.

Types of noncancerous breast lump

The majority of breast lumps are not cancerous. A person may develop one of the following benign breast lumps:

Fibroadenoma
Fibroadenoma is the most common type of noncancerous tumor that affects the breast. A fibroadenoma is a tumor made up of glandular and connective tissues. A fibroadenoma feels like a small, round marble in the breast. Fibroadenomas also have the following characteristics:

• Clear-cut borders
• Moveable under the skin
• Firm or rubbery
• Not tender

Fibroadenomas are usually very small, around 2.5 centimeters in diameter. Some are too small to feel, but they will show up on mammograms and ultrasounds. Others can be several inches across. Fibroadenomas are most common among women who are in their 20s and 30s, and they tend to shrink after menopause. It is possible to have more than one fibroadenoma. According to the American Cancer Society (ACS), having a fibroadenoma can slightly increase a person's risk of breast cancer. Not all fibroadenomas require treatment. Some will shrink or even disappear on their own. A doctor will usually recommend removing the fibroadenoma if it grows or causes changes within the breast. Learn more about breast fibroadenomas here.

Breast cysts
Breast cysts are round sacs of fluid that can develop in breast tissue. Around 25% of masses in the breast are cysts, which are benign and do not affect someone's risk of breast cancer. Breast cysts mainly affect women in their 40s, but people can develop breast cysts at any age. Symptoms of breast cysts include:

• One or more round, movable masses under the breast skin
• Smooth, rubbery texture
• Lumps that are tender or painful to the touch

Doctors use ultrasound tests to diagnose breast cysts. Cysts that contain only fluid do not need treatment unless they are very large or cause discomfort. If the cyst appears solid or has solid areas on the ultrasound image, the doctor may recommend a biopsy to rule out breast cancer.

Fibrocystic breast changes
Fibrocystic breast changes occur when hormonal changes during menstruation cause lumpiness in one or both breasts. Fibrocystic breast changes happen over time and over repeated menstrual cycles. They can cause some discomfort, but they do not increase the risk of breast cancer. Other symptoms of fibrocystic breast changes include:

• Tenderness or pain in the breast
• Pain under the arms
• Green or brown nipple discharge

Fibrocystic breast changes do not require medical treatment. Taking over-the-counter (OTC) pain relievers and using warm compresses can help relieve uncomfortable or painful symptoms. Although fibrocystic breast changes are often harmless, they can make detecting breast cancer through breast self-examinations more difficult. This is why it is essential for people to get screened for breast cancer regularly. Learn more about fibrocystic breast changes here.

Intraductal papilloma
An intraductal papilloma is a noncancerous tumor that develops in the milk ducts of the breast. These growths are a common cause of nipple discharge. People can have one near the nipple, or a cluster of small tumors in the narrow milk ducts farther from the nipple. Symptoms of intraductal papilloma include:

• Swelling of the breast
• One or more lumps close to or behind the nipple
• Clear or bloody nipple discharge

Having one intraductal papilloma does not affect a person's risk of breast cancer, but having several can increase the risk slightly. Doctors may treat intraductal papillomas by surgically removing the papilloma along with the affected area of the milk duct.

Lipoma
A lipoma is a collection of fat cells. They can develop anywhere on the body. Lipomas usually appear just below the skin, but they can also form inside the mammary glands. Lipomas are soft, moveable lumps that do not cause pain. A lump is usually the only symptom. Lipomas in the breast do not increase the risk of breast cancer.

Breast infection
Mastitis is an infection in the breast tissue. A blocked milk duct or bacteria entering the breast can cause a breast infection. This may be more common while breastfeeding. Symptoms of mastitis include:

• A lump in the breast that is tender or sore to the touch
• Redness and swelling of the breast
• Pain or sensitivity when touching the affected area
• A warm or a burning sensation in the affected area

Treatments for mastitis include taking antibiotics and over-the-counter pain relievers. Untreated mastitis can develop into a collection of pus, or an abscess, in the breast tissue. If an abscess forms, a person may need surgery to drain the pus. Learn more about breast infections here.

Adenosis
Adenosis is a noncancerous breast condition characterized by abnormally large lobules in the breast. Adenosis can cause a lump that feels similar to a cyst or a tumor. The enlarged lobules can contain calcium deposits, which makes it difficult for a doctor to tell them apart from tumors on a mammogram. A doctor will use a biopsy to determine if the lump is adenosis or breast cancer. There is some debate around whether or not adenosis increases the risk of developing breast cancer. Biopsies are minimally invasive procedures. Before a biopsy, a medical professional will give the person a local anesthetic. During the procedure, they will use a thin needle to remove a small sample of tissue for laboratory testing. People who have adenosis do not need treatment, but they can get regular checkups to watch out for warning signs of breast cancer.

Phyllodes tumor
Phyllodes tumors are rare, making up less than 1% of all breast tumors. Most are benign, but around 1 in 4 are malignant, or cancerous. Some phyllodes tumors are borderline, meaning that they fall between benign and malignant. Phyllodes tumors feel like hard, painless masses. A doctor will usually perform a biopsy to diagnose these tumors because they are difficult to identify using mammograms and ultrasounds. Surgery is the main treatment for phyllodes tumors. People who have had phyllodes tumors removed will need regular follow-ups and breast exams, as these tumors can return after treatment.

Breast cancer
Breast cancer is a collection of abnormal cells that develop in the tissue, ducts, or lobules of the breast. Breast cancer cells divide and multiply rapidly to form tumors that starve the surrounding tissue. Breast cancer tumors are usually hard, irregular in shape, and painless. Early diagnosis of breast cancer is vitally important. Some people can develop breast cancer symptoms before they notice a lump in the breast. Some of these symptoms include:

• Swelling or pain in the breast
• Redness, irritation, or rash on the breast skin
• Dimpling of the breast skin
• Changes in the appearance of the breast or nipple
• Nipple discharge

Diagnosis

To assess a breast lump, a health-care professional will review a person's medical history and perform a physical examination of the breast. They may then use imaging tests to see if the lump is benign or cancerous. Such tests may include the following:

• Mammograms, which involve taking x-ray photos of the breast tissue
• Ultrasound scans, which doctors use to investigate abnormal findings from physical exams or mammograms
• Magentic resonance imaging (MRI) scans, which create detailed images of the breast to investigate abnormal findings from physical exams or mammograms

People who have a very high risk of developing breast cancer can have screening MRI scans. If a doctor is still unsure about the nature of a breast lump after performing imaging tests, they may recommend a biopsy to determine if the lump is benign or cancerous.

When to see a doctor

While most breast lumps are benign, people should have a health-care professional check any new or unusual breast lumps. It is especially important for people to seek medical attention if they have a breast lump and any of the following warning symptoms of breast cancer:

• A hard lump inside the breast, near the collarbone, or under the arm
• Swelling, redness, or rash on the breast skin
• Dimpling or puckering of the breast skin
• Changes in the size or shape of the breast
• Changes in the shape of the nipple
• Nipple turning inward, or retraction
• Unusual nipple discharge
• A new lump that does not go away after one full menstrual cycle
• Unintentional weight loss

Outlook

Most breast lumps are benign. If a person finds a lump in either breast or both, they should try to stay calm and schedule an appointment so that a doctor can look at it.

In the US, breast cancer is the most common cancer among women, apart from skin cancers. The average risk of a woman developing breast cancer in her lifetime is around 12%. Regular breast screening, such as self-breast examinations and mammograms, plays a vital role in the early detection of breast cancer. The National Breast Cancer Foundation recommends performing breast self-exams once every month. Learn how to perform a breast self-exam here. The ACS state that women aged 45–54 years should have annual mammograms. All breasts are different, so what might be normal for one person may not be for another. People should try to become familiar with their breasts, so that they can inform their doctor of any changes.