CHICAGO — The American Cancer Society now says women should start mammograms later in life and get fewer of them, a stance that puts the trusted group closer to an influential government task force’s advice.

In new guidelines out Tuesday, the cancer society recommends that most women should begin annual screening for breast cancer at age 45 instead of 40, and switch to every other year at 55. The task force advises screening every other year starting at age 50.

It’s not a one-size-fits-all recommendation; both groups say women’s preferences for when to be scanned should be considered.

The advice is for women at average risk for breast cancer. Doctors generally recommend more intensive screening for higher-risk women, including those with specific genetic mutations.

“The most important message of all is that a mammogram is the most effective thing that a woman can do to reduce her chance of dying from breast cancer,” said Dr. Richard Wender, the cancer society’s cancer control chief.

“It’s not that mammograms are ineffective in younger women,” he said, but at age 40, breast cancer is uncommon and false alarms are more likely. “Therefore, you’d have to do a lot more mammograms to prevent one death,” compared to older women, Wender said.

Concern about false alarms contributed to the cancer society’s new guidance. These lead to worry and more testing — they mean an initial result was suspicious but that cancer was ruled out by additional scans and sometimes biopsies.

The latest guidelines acknowledge that some younger women are willing to accept that, and that for them starting annual exams at age 40 is fine, as long as they know the risks.