We’ve all been there. You walk upstairs only to find yourself wondering why you bothered. You blank on an acquaintance’s name, just as you’re introducing them. Or maybe, after a frantic search, you find your car keys in the fridge of all places.

Such momentary lapses of memory can be disconcerting, but they are part and parcel of getting older, and very much to be expected. “Decline in what researchers call episodic memory – what happened, where and when – is a normal part of human cognitive ageing,” says Ulman Lindenberger, a cognitive neuroscientist and director of the Max Planck Institute for Human Development in Berlin. “In most adults, decline becomes apparent in their 60s… and it affects all stages of memory, from the encoding of new events over consolidation to retention and recall.”

This is largely explained by structural and functional changes to the brain that begin in middle age and accelerate from there. In a 2025 paper analysing more than 3700 “cognitively healthy” adults, Lindenberger and his colleagues found age-related memory decline tracks closely with the deterioration of connections between brain regions, itself the result of the gradual degradation of the fatty coating that insulates neurons, and shrinkage of the hippocampus – a brain region crucial in forming new memories.

This is nothing to worry about, says Lindenberger. “Learning and episodic memory are all about forming new, and remembering previously formed, associations – and the corresponding machinery of our brains becomes less reliable with advancing adult age.”

What’s more, in many cases, everyday memory failures are actually just failures of attention: if your brain never properly encoded where you put your keys because you were distracted or stressed in the moment, there isn’t much in the way of memory to retrieve later.

Where “normal” memory slowdown becomes something more suspicious, however, is harder to say.

Broadly speaking, neurologists themselves take notice when incidental forgetfulness becomes a pattern that interferes with daily functioning – when you forget things you used to remember, or when you forget important things – and when memory loss accelerates in such a way that others notice. “We get concerned when individuals start to forget important information like doctor’s appointments or golf tee times,” says Ronald Petersen, a neurologist at the Mayo Clinic in Minnesota. “When it starts to become a pattern and those around you notice these episodes, it might be time to seek attention.”

Petersen says one way to think about what constitutes a pattern might be to think about whether you, or someone you’re concerned about, repeats themselves – and crucially, how frequently – because that can serve as a decent metric for the extent to which memory function may be declining in an accelerating fashion. “Tending to repeat oneself, without awareness, on a frequent basis… that might be worrisome,” says Petersen.

The reason conversational repetition is a good indicator has to do with what happens in the brain in mild cognitive impairment, the transitional stage between typical ageing and dementia, and early-stage dementia. In Alzheimer’s disease, by far the most common form of dementia, some of the earliest changes occur in the hippocampus and entorhinal cortex – which are crucial for encoding and consolidating new episodic memories – meaning that people affected struggle disproportionately with forming new memories, of a recent conversation, for instance, rather than with recalling established memories. If someone asks the same question several times in the space of an afternoon, it may be because the memory of asking the question never properly formed in the first place – which is a potential red flag.

Whether it’s conversational repetition or getting lost in familiar places, another widely cited cause for concern, there is no hard-and-fast rule when it comes to what kinds of forgetfulness indicate something more serious than typical age-related memory loss. “In advanced old age, the line between the lower range of normal [age-related memory decline] and dementia is difficult to draw,” says Lindenberger. Put simply, the problem is that there isn’t a sharp distinction, in terms of behaviour, or even biology, between the two.

Everything from anxiety, stress and depression to menopause and medications have been shown to temporarily impair attention and episodic memory. So, it is always worth considering what else might lie behind signs of cognitive impairment before jumping to conclusions. We should also be wary of over-interpretation. A 2025 study showed that older adults with high levels of what researchers call “dementia worry” are more likely to interpret everyday memory lapses as signs of impending cognitive decline than those in a control group, which is itself associated with negative health outcomes.

The truth is that knowing what is “normal” and when to worry about memory loss in old age is difficult even for neurologists – never mind for the rest of us. Ultimately, then, perhaps the best rule of thumb is, as Lindenberger says, that “there is reason to be concerned when [memory] decline is fast and starts to interfere with daily routines”.