A mammogram is a low-dose X-ray of the breast designed to detect cancer before you can feel a lump. The procedure takes about 20 minutes and involves compressing each breast between two plates while a machine captures images of the tissue inside. It remains the most widely used tool for finding breast cancer early, when treatment is most effective.
How the Imaging Works
During a mammogram, each breast is placed on a flat plate and gently compressed by a second plate from above. This compression spreads the tissue so the X-ray can capture a clearer picture with less radiation. The technologist takes images from at least two angles per breast, typically from top to bottom and side to side. The entire process is quick, with each compression lasting only a few seconds.
Most facilities now offer 3D mammography, also called tomosynthesis, which takes multiple thin images and assembles them into a layered view. Compared to standard 2D mammograms, 3D imaging finds more cancers and reduces the chance of being called back for a false alarm. If your facility offers 3D, it’s generally the better option.
Screening vs. Diagnostic Mammograms
A screening mammogram is the routine version, done when you have no symptoms or concerns. Its purpose is to catch problems that haven’t produced any signs yet. The U.S. Preventive Services Task Force recommends screening every two years starting at age 40 and continuing through age 74.
A diagnostic mammogram is ordered when something specific needs investigation: a lump you or your doctor found, nipple discharge, skin changes, or an unclear finding on a previous screening. Diagnostic mammograms use the same machine but take images from more angles, which means slightly more radiation and a longer appointment. The radiologist often reads the images while you’re still at the facility so additional views can be taken right away if needed.
How to Prepare
On the day of your mammogram, skip deodorant, perfume, and powder under your arms or on your chest. These products contain particles that can show up as white spots on the X-ray and mimic the appearance of calcifications, potentially leading to a confusing image. If you forget, most facilities have wipes available so you can clean off the product before imaging.
Wearing a two-piece outfit makes things easier since you’ll need to undress from the waist up. If your breasts tend to be more tender before your period, scheduling your appointment for a week or two after your period starts can help reduce discomfort during compression.
What Compression Feels Like
The compression is the part most people ask about. It ranges from mildly uncomfortable to genuinely painful, depending on your breast size, density, and sensitivity. Studies show that breast size alone doesn’t predict how much discomfort you’ll feel, though women with less dense breast tissue tend to report less pain. Each compression lasts only a few seconds, and the discomfort stops as soon as the plates release.
Knowing what to expect actually helps. Research has found that women who receive clear explanations of the procedure beforehand report less pain during it. Some facilities use foam pads on the compression plates, which has been shown to noticeably reduce discomfort. If you’re anxious about pain, you can ask whether your facility offers these pads. Taking a mild over-the-counter pain reliever an hour beforehand may also help with moderate discomfort, though results on this are mixed.
Getting Your Results
Federal law requires that every mammography facility send you a written summary of your results in plain language within 30 days. In practice, many facilities deliver results much faster, often within a week or even a few days. If something looks abnormal, the American College of Radiology recommends contacting patients within five days.
Your results come with a score on a standardized scale from 0 to 6. Here’s what each category means in practical terms:
- Score 0: The images weren’t complete enough to make a call. You’ll be asked to come back for additional views or an ultrasound. This is common and doesn’t mean something is wrong.
- Score 1: Completely normal. Nothing unusual was seen.
- Score 2: Something was found, but it’s clearly benign, like a cyst or a calcified lump. No follow-up needed beyond your regular screening schedule.
- Score 3: Probably benign, with less than a 2% chance of being cancer. You’ll typically be asked to come back in six months to confirm the finding hasn’t changed.
- Score 4: Suspicious. This category is subdivided into low (2% to 10% chance of cancer), intermediate (10% to 50%), and high suspicion (50% to 95%). A biopsy is usually recommended.
- Score 5: Highly suspicious, with a greater than 95% chance of being cancer. A biopsy will be performed promptly.
- Score 6: Cancer that has already been confirmed by biopsy. This score is used for tracking during treatment.
What Callbacks and False Positives Mean
Getting called back after a screening mammogram is stressful, but it’s also common. About 10% of screening mammograms result in a callback for additional imaging. Of all screens, only about 1.3% lead to a biopsy recommendation, and many of those biopsies come back benign. Over the course of ten years of annual screening, roughly half of all women will experience at least one false-positive recall. That’s a normal part of the screening process, not a sign that something went wrong.
The goal of callbacks is to get a closer look at something the radiologist couldn’t fully evaluate on the initial images. Most of the time, the additional views or ultrasound clears the concern entirely.
Dense Breasts and Screening Accuracy
Breast density matters more than most people realize. Dense tissue appears white on a mammogram, and so do tumors, which means dense tissue can hide cancers in plain sight. In women with very dense breasts, mammogram sensitivity can drop to as low as 25% to 30%, compared to nearly 100% in women with mostly fatty breast tissue. That’s a dramatic difference.
Since 2024, the FDA has required all mammography centers to notify you if you have dense breasts. About half of women over 40 have dense breast tissue. If your results letter mentions dense breasts, it’s worth discussing supplemental screening options with your doctor. Breast ultrasound and MRI are the most common additions and can catch cancers that mammograms miss in dense tissue. Dense breasts are normal and very common; they just require a more complete screening strategy.