For the past 50 years women have been urged to have regular mammograms, breast X-rays that help healthcare providers find suspicious lumps. But experts have disagreed about exactly when women should begin to get this breast cancer screening test.

The U.S. Preventive Services Task Force (USPSTF) says women at average risk of breast cancer should start screenings at age 50, and the American Cancer Society recommends starting at 45. And this year, the American College of Obstetricians and Gynecologists (ACOG) updated its recommendations to advise women to start screening no later than age 50 but with the choice to begin sooner, in their 40s.

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ACOG’s change acknowledges that all of the potentially conflicting screening strategies have merit, says Chris Zahn, M.D., its vice president for practice activities. Though all three groups work from the same body of research, the results are open to different interpretations that can lead to differing advice, he says.

ACOG’s update resolves some of that conflict by emphasizing the importance of a woman’s individual decision-making within a set of rough guidelines, rather than telling women exactly what to do.

“There has been so much confusion around the guidelines and how different they are,” says Lisa Schwartz, M.D., a professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice. Schwartz wasn’t involved in crafting the new guideline.

The recent update to ACOG’s guideline, which suggests that the mishmash of advice is “starting to come together,” Schwartz says, should help ease some of that confusion.

“Women trying to decide when to get a mammogram need to understand the evidence, and they should consider their own cancer worries so that they make informed choices that are right for them,” says Marvin M. Lipman, M.D., Consumer Reports’ chief medical adviser.

In light of National Mammography Day, here’s what the different groups recommend and what to consider:

Weighing Testing's Benefits and Harms

The benefits of mammograms are obvious, Lipman says: fewer deaths from breast cancer. The American Cancer Society, for example, points to research involving hundreds of thousands of women showing that regular screening has cut breast cancer deaths by 35 to 50 percent.

The risks of breast cancer screening, though less familiar to consumers and even to some doctors, are of increasing concern to many experts. The two main risks:

False alarms: Mammograms often cause false positives, results that initially seem worrisome but prove to be harmless on follow-up tests. For example, a recent review by the USPSTF found that 42 percent of women who are screened every two years for 10 years starting at age 50 will have at least one false positive. 

Getting screened every year makes it more likely that you’ll experience a false alarm, as does starting in your 40s, Lipman notes. False alarms can cause needless anxiety and lead to more mammograms, which expose you to radiation and sometimes to unnecessary biopsies.

Overtreatment: Some cancers detected by mammography and then treated are unaggressive tumors that would never have caused harm. Treating these cancers subjects women to stress and the potential risks of cancer therapy—surgery, chemotherapy, and radiation—without any benefits.

The task force estimates that at least one in eight tumors detected by mammography would never have spread, and that for every woman whose life is saved by mammography, two or three will be treated without good reason.

Factoring Your Breast Cancer Risks

It’s important to note, Schwartz says, that the recommendations from the three major groups are directed at women of average risk for breast cancer.

That means if you’re at high risk—if you’ve had breast cancer before, you have a first-degree relative who had breast cancer, you had genetic testing and know you carry a BRCA1 or BRCA2 genetic mutation, or you have a history of multiple chest X-rays or radiation treatments to the chest​ (as with lymphoma therapy)—these recommendations don’t apply to you. You’ll need to talk with your doctor about an optimal screening strategy.

But if you’re not in that group, other, less weighty risk factors may help you decide when to get your first mammogram and how often to screen. These risk factors include:

• A personal history of noncancerous breast conditions, including atypical hyperplasia or dense breasts.
• Menstrual periods that started before age 12 or continued after 55, or not having a child before 30.
• A history of hormone replacement therapy.
• Obesity, smoking, or excessive alcohol consumption.

The higher your risk, the more aggressive you may want to be, for example, starting at age 40 or 45 instead of 50 or getting screened once per year instead of every two years, Lipman says.

4 Key Questions to Consider

Below are the questions to consider, the positions of leading health groups on each issue, and the advice of our experts.

1. When Should You Start Screening?

American College of Obstetricians and Gynecologists: No later than 50, but with the option to start at 40.
American Cancer Society: Start at 45, but with the option to start at 40.
U.S. Preventive Services Task Force: Start at 50, but with the option to start at 40.

What to know: Breast cancer becomes much more common after age 50, and starting screenings sooner increases the chance of false alarms and possibly unnecessary treatment. On the other hand, cancers that develop before menopause tend to be more aggressive, making it more important to catch them early.

CR’s take: The more risk factors you have for breast cancer, and the less concerned you are about the chance of being called back for more tests or receiving treatment unnecessarily, the more reasonable it is to start having mammograms in your 40s.

2. How Often Should You Have a Mammogram?

American College of Obstetricians and Gynecologists: Every year or every two years, depending on preference.
American Cancer Society: Every year from age 45 to 54, then every two years.
U.S. Preventive Services Task Force: Every two years.

What to know: Breast cancer that appears before menopause tends to spread faster. But frequent tests make false alarms and unnecessary treatment more likely.

CR’s take: If you opt to screen in your 40s, annual tests make sense, switching to tests every other year when you reach age 50 or so. People who start screening in their 50s may be better off with testing every other year, Lipman says. 

3. When Should You Stop?

American College of Obstetricians and Gynecologists: Women 75 and older should talk with their doctor about whether testing continues to make sense for them.
American Cancer Society: Continue as long as you have a life expectancy of 10 or more years.
U.S. Preventive Services Task Force: Not enough evidence to recommend screening after 74.

What to know: There’s little hard evidence for the benefits of breast cancer screening for women 75 and older. Although researchers know that about a quarter of breast cancer deaths occur in women older than that, they also say that the older and sicker you are, the less likely it is that mammography will extend your life.

CR’s take: The American Cancer Society’s advice to consider your overall health and life expectancy makes sense. A woman already diagnosed with a different kind of cancer or dealing with another serious health problem—such as chronic obstructive pulmonary disease or heart failure—might want to focus more on managing those problems. Someone in good health, however, might prefer to continue screening, especially if she has risk factors for breast cancer, Lipman says.

4. What About Breast Exams?

American College of Obstetricians and Gynecologists: Women 25 to 39 should have the option to screen every one to three years, and women 40 and older should receive them every year.
American Cancer Society: Not recommended.
U.S. Preventive Services Task Force: There's not enough evidence for or against to make a recommendation.

What to know: Though having your doctor check your breasts for lumps (or doing so yourself) may seem sensible, little research backs up the practice, Lipman notes. Instead, these exams may create anxiety and lead to needless follow-up tests.

CR’s take: If you notice something abnormal, tell your doctor.

Correction: This article has been updated. The American College of Obstetricians and Gynecologists recommends that women should start getting mammograms no later than 50, not starting at 50.