Q. When is memory loss a normal sign of aging, and when is it a problem?

A. Suzanne Salamon, a geriatrician at Beth Israel Deaconess Medical Center, says that it’s a bit of a misconception that memory loss is a normal part of aging. While it takes older people longer to learn new information or skills, “usually people’s memories stay pretty much the same,’’ she says, and many healthy elderly people remain mentally sharp even if their cognitive abilities have slowed.

What many people might think of as memory loss - misplacing your keys or forgetting an appointment - is considered mild forgetfulness. Salamon says distraction often plays a role: Our brains aren’t adept at multitasking and fail to retain information without our full attention. In contrast, people who are exhibiting signs of an aging-related memory disorder such as Alzheimer’s disease will not only forget to go to an appointment but forget they made it in the first place. They may repeat the same information within a conversation, unaware they said it before. They forget how to navigate familiar places and fail to take care of themselves in simple ways.

Memory lapses can be a sign of mild cognitive impairment, a condition that is not fully understood but involves limited memory problems such as mixing up words, forgetting how to do certain tasks, and frequently losing things. Only some people who have this condition go on to develop Alzheimer’s disease.

The two most common causes of serious age-related memory loss are Alzheimer’s disease and vascular dementia (caused by a series of small strokes in the brain). If you suspect a loved one has a memory disorder, it’s important to broach the topic and encourage the person to see a medical professional.