Memory-loss cause #8: Normal aging

Why it happens: Memory lapses aren't always a sign that something's wrong. Sometimes they're normal. After all, the brain starts its gradual decline as early as during one's late 20s and early 30s. By the late 40s and early 50s, most people get that "now why did I come into this room?" feeling and have occasional trouble remembering names of new acquaintances or items on shopping lists.

Dementia, such as Alzheimer's, isn't a normal part of aging. But occasional forgetfulness does tend to increase as we get older.

What else to look for:

• How old are you? The risk of Alzheimer's increases with age. The likelihood of developing it doubles every five years after age 65, according to the Alzheimer's Association. About one in two people over 85 have it. Of course, this means half don't.

• Are you finding it harder to learn new things? That can happen normally with age, as the ability to form new memories sometimes slows. But with Alzheimer's, following multiple steps is difficult-to-impossible, and new knowledge isn't retained well because these memories don't get formed. Also with Alzheimer's, memory troubles tend to affect not just new tasks but old familiar ones as well.

• Are you scared? The irritation of forgetting an appointment is different from the deeper fear inspired by, say, forgetting how to use the telephone, says University of Wisconsin geriatric psychiatrist Ken Robbins.

• Are others mentioning their concern to you? People with Alzheimer's are often unaware that they're even having memory troubles -- so if you're worrying, you may be just fine, experts say.

• Can you still pretty much carry on your everyday life? With Alzheimer's, the answer is clearly no.