A mammogram is a low-dose X-ray image of the breast used to detect cancer and other abnormalities, often before they can be felt. It is the standard screening tool for breast cancer and takes roughly 10 to 15 minutes. The U.S. Preventive Services Task Force recommends that all women get a screening mammogram every two years starting at age 40 and continuing through age 74.
How the Procedure Works
During a mammogram, your breast is placed on a flat platform and compressed with a clear plastic paddle. The compression spreads the tissue so the X-ray can capture a clearer picture with less radiation. You’ll need to hold very still, and you may be asked to hold your breath for a few seconds to prevent blurring. A standard screening exam takes four images: two of each breast, one from top to bottom and one from side to side.
The compression can feel uncomfortable or even painful, but it lasts only a few seconds per image. The entire appointment, including positioning, is typically done in under 20 minutes.
Screening vs. Diagnostic Mammograms
There are two types, and they serve different purposes.
A screening mammogram is for women with no breast symptoms. It’s a routine check designed to catch cancer early, before any lump or change is noticeable. Four standard views are taken, and results usually come back within a few days because radiologists prioritize reading diagnostic exams first.
A diagnostic mammogram is ordered when something specific needs investigation: a lump, focal pain, nipple discharge, or an abnormal result from a previous screening. The technician places a small marker on your breast to flag the area of concern, and the radiologist reviews the images in real time while you’re still in the office. Additional views with extra compression or magnification may be taken, and an ultrasound is often performed during the same visit. You’ll typically get your results the same day.
What 3D Mammograms Add
Many imaging centers now offer 3D mammography, also called digital breast tomosynthesis. Instead of a single flat image, the machine captures thin slices of the breast from multiple angles and assembles them into a layered picture. This is especially useful for women with dense breast tissue, because a standard 2D image can make it hard to distinguish normal dense tissue from a potential tumor. Both appear white on the image.
3D mammograms slightly increase the number of cancers found during screening and reduce the chance that you’ll be called back for additional imaging due to an unclear result.
How to Prepare
Skip deodorant, antiperspirant, powder, and lotion on your underarms and chest the day of your appointment. The aluminum in antiperspirants shows up on the X-ray as tiny bright specks that look almost identical to calcifications in the breast. These artifacts can mimic suspicious findings and lead to unnecessary follow-up testing. If you forget, most facilities will offer wipes to clean the area before your exam.
Try to schedule your mammogram for a time when your breasts are least tender, which for many women is the week after a menstrual period. Wear a two-piece outfit so you only need to remove your top.
Understanding Your Results
Radiologists score every mammogram on a standardized scale from 0 to 6. Knowing what these numbers mean can save you a lot of anxiety if you see them on your report.
- Category 0 (Incomplete): The images weren’t clear enough to make a call. You’ll be asked to come back for additional views or to bring in prior mammograms for comparison.
- Category 1 (Negative): Completely normal. No findings of concern.
- Category 2 (Benign): Something was seen, like a cyst or calcification, but it’s clearly not cancer. This is still considered a normal result.
- Category 3 (Probably benign): A finding with no more than a 2% chance of being cancer. A follow-up mammogram in 6 to 12 months is typically recommended to confirm the finding stays stable, usually over at least two years.
- Category 4 (Suspicious): The radiologist recommends a biopsy. The likelihood of cancer ranges from just above 2% at the low end to above 50% at the high end, depending on the sub-classification.
- Category 5 (Highly suspicious): The finding has at least a 95% chance of being cancer. A biopsy is strongly recommended.
- Category 6 (Known cancer): Used only when a biopsy has already confirmed cancer and the mammogram is being used to guide treatment planning.
Getting a category 0 callback is common and does not mean something is wrong. It often just means the image needs a second look.
Why Dense Breasts Matter
About half of women over 40 have dense breast tissue. Density isn’t something you can feel; it’s determined by the mammogram itself. Dense tissue appears white on the image, and so do tumors, which means cancer can essentially hide in plain sight. Mammograms are less sensitive in women with dense breasts, and these women are more likely to be called back for follow-up imaging.
Supplemental screening with ultrasound or MRI may be an option if you have dense breasts, though guidelines have not yet settled on a firm recommendation for or against routine additional imaging. Many states now require that imaging centers notify you in writing if your mammogram shows dense tissue, so you can discuss next steps with your doctor.
Radiation Exposure
A screening mammogram delivers about 0.7 millisieverts of radiation across all four images. To put that in perspective, you absorb roughly the same amount from natural background radiation, things like cosmic rays and radon in the soil, over about 24 weeks of everyday life. The dose is small enough that the benefit of catching breast cancer early far outweighs the minimal radiation risk.
Cost and Insurance Coverage
Under the Affordable Care Act, all Marketplace health plans and most other insurance plans must cover screening mammograms for women 40 and older with no copay, coinsurance, or deductible. This applies to mammograms done every one to two years. Diagnostic mammograms, because they’re ordered to investigate a specific problem, may be billed differently and could involve out-of-pocket costs depending on your plan.