Mammography and screening basics: what to expect

A mammogram is one of the few scans many people have on a schedule, long before anything is wrong. That makes it feel different from a scan ordered for a symptom, and it raises its own questions: why the squeeze, what a call-back means, and why advice about when to start differs from one country to another. This page explains the examination and the terms around it, using public sources. It does not recommend an age or an interval for anyone. Those choices depend on your country's programme, your history and a conversation with your own doctor. How mammography sits among the other scans is covered in types of medical imaging.

What a mammogram is

RadiologyInfo.org describes mammography as specialised medical imaging that uses a low-dose X-ray system to see inside the breasts. The FDA likewise calls a mammogram a low-dose X-ray picture of the breast that can find breast lumps often before they are big enough to feel or symptoms appear. There are two broad purposes. Screening mammography is for people with no symptoms. Diagnostic mammography is used to evaluate a lump, nipple discharge or another finding that has been noticed, and may also be done after an abnormal screening mammogram to look at the area of concern.

Modern mammography is digital. RadiologyInfo.org says digital systems replace film with electronics that convert X-rays into pictures, which allows better pictures with a lower radiation dose. A more recent form is breast tomosynthesis, also called three-dimensional or 3-D mammography, in which multiple images from different angles are reconstructed into a three-dimensional image set. The same page compares it to CT, where thin "slices" are assembled, and reports that large population studies have shown improved cancer detection rates and fewer call-backs with tomosynthesis screening. It also notes that the radiation dose for some tomosynthesis systems is slightly higher than for standard mammography but remains within the FDA-approved safe levels.

For dose figures, RadiologyInfo.org's dose table lists screening digital mammography at 0.28 mSv, comparable to 34 days of natural background radiation, and screening digital breast tomosynthesis at 0.34 mSv, comparable to 42 days. The page cautions that actual doses vary. The dose page explains how to read such numbers: see radiation, contrast and imaging safety.

The appointment, and why the squeeze

During the exam a radiologic technologist positions each breast on a platform and gradually compresses it with a clear plastic paddle. You will be asked to change position between images, and the routine views are a top-to-bottom view and an angled side view. RadiologyInfo.org says the exam should take about 30 minutes. You must hold very still, perhaps hold your breath for a few seconds, while the technologist takes the X-ray from behind a wall or in the next room.

The compression is the part people dread, so the reasons are worth knowing. The source gives them: it evens out the breast thickness so all of the tissue can be seen, spreads the tissue so small abnormalities are less likely to be hidden, allows a lower X-ray dose because a thinner amount of tissue is imaged, holds the breast still to minimise blurring and reduces scatter. You will feel pressure, and some people with sensitive breasts feel discomfort. The page says to tell the technologist if pain occurs, because if discomfort is significant, less compression will be used.

Preparing for a mammogram

RadiologyInfo.org lists a few practical points, attributing them to the American Cancer Society. If your breasts are usually tender in the week before your period, do not schedule the mammogram then; the best time is one week after your period. Do not wear deodorant, talcum powder or lotion under your arms or on your breasts that day, because these can appear on the image as calcium spots. Describe any breast symptoms to the technologist, and tell your doctor about prior surgery, hormone use and any personal or family history of breast cancer. If earlier mammograms were done elsewhere, bring them or have them sent, because comparison is needed. Always tell the staff if there is any possibility that you are pregnant.

One line from the source is worth repeating as written: ask when your results will be available, and do not assume the results are normal if you do not hear from your doctor or the facility. More on the day itself is in preparing for a scan and your results.

Who is screened, and when, depends on where you live

There is no single worldwide schedule, and sources show it. RadiologyInfo.org states that current guidelines from the American College of Radiology and the National Comprehensive Cancer Network recommend screening mammography every year for women beginning at age 40, and says the ACR and the National Cancer Institute suggest that people at increased risk, for example through family history, should seek expert advice about starting earlier and about other types of screening. By contrast, the NHS in England offers breast screening to women aged 50 up to their 71st birthday, with a first invitation between 50 and 53 and then an invitation every 3 years. The NHS page also explains how trans and non-binary people are invited. Neither set of figures is a recommendation for you; your national programme and your doctor can tell you what applies.

Results, call-backs and breast density

A radiologist analyses the images and sends a signed report to your doctor, who discusses the results with you, and the mammography facility also notifies you. A call-back is when you are asked to return for more testing. RadiologyInfo.org says five percent to 15 percent of screening mammograms require more testing, such as additional mammograms or ultrasound, and that most of these turn out to be normal. It estimates that a woman who has yearly mammograms between ages 40 and 49 has about a 30 percent chance of a false-positive mammogram at some point in that decade and about a 7 percent to 8 percent chance of a breast biopsy within the 10-year period. Those are the source's figures for that group, not predictions for any individual.

Breast density is part of results in some countries. The FDA says approximately half of women over the age of 40 in the U.S. have dense breast tissue, that dense tissue can make cancers more difficult to detect on a mammogram, and that dense breasts have been identified as a risk factor. Under rules effective September 2024, the FDA says U.S. facilities must give each patient a written summary about breast density and report one of four density categories to the health care provider. If the summary says your breasts are dense, the FDA's advice is to discuss your questions with your provider, including whether any next steps are needed. RadiologyInfo.org adds that not all breast cancers can be seen on mammography, that a normal breast looks different for each woman, and that implants can block the view of nearby tissue.

The short version

A mammogram is a low-dose breast X-ray, used for screening and for investigating symptoms, with compression that is uncomfortable but has reasons behind it. Sources agree on the practical preparation steps, while screening ages and intervals differ between countries and guidelines, so the right schedule is one to settle with your own doctor or national programme.