Only 15% of the 1,100 patients and caregivers surveyed brought up their observations right away, and 11% still haven’t, according to the survey, released Monday by the London-based Alzheimer’s Society. Participants included diagnosed dementia patients and their caregivers, as well as potential dementia patients and their caregivers.

Nearly a quarter of those surveyed waited more than six months before seeking medical help, the survey found. The most common reason for staying silent wasn’t anxiety about the condition, which is generally progressive. Rather, those affected weren’t sure exactly which symptoms are associated with normal aging and which are associated with dementia.

Case in point: legendary actor Bruce Willis. In a May 31 essay in Vogue, daughter Tallulah Willis opened up about her dad’s 2022 diagnosis with aphasia, which impairs the ability to speak, understand speech, and to read and write. She also discussed his broader diagnosis of frontotemporal dementia, which typically occurs in people ages 45 to 64. Unusual behaviors, trouble managing emotions, and difficulty communicating and walking are hallmarks of the condition, according to the National Institute on Aging.

Like so many other caregivers, she says the signs of her father’s cognitive decline are clear, looking back. At the time, however, she chalked up his “vague unresponsiveness” to “Hollywood hearing loss.”

“I’ve known that something was wrong for a long time,” she confessed, adding that family members would often encourage each other to “speak up! Die Hard messed with Dad’s ears.”

“Later that unresponsiveness broadened, and I sometimes took it personally,” she added.

Confusion, stigma, and anxiety around dementia—which will affect a third of individuals over their lifetime—delay diagnosis and treatment, Kate Lee, CEO of the Alzheimer’s Society, said in a news release about the study.

“We can’t continue to avoid the ‘d’ word,” she said. “We need to face dementia head on.”

How to tell the difference between aging and dementia

“Dementia is definitely not normal aging,” Dr. John Schumann—executive medical director of Oak Street Health, a chain of primary care clinics that serve older adults—tells Fortune.

Dr. David Reuben, director of the Multicampus Program in Geriatric Medicine and Gerontology at the UCLA David Geffen School of Medicine, agrees. He equates aging, a normal biological phenomenon, to a “computer processor up in your brain that doesn’t work quite as quickly.” An example: A word or phrase is “on the tip of your tongue,” and you find yourself saying, “give me a couple of minutes and it will pop back in.” Such retrieval deficits are “very common with aging,” he says.

Dementia is an umbrella term for a wide range of disorders involving a progressive or persistent loss of intellectual functioning, from mild to severe, with Alzhermier’s being the most common. While some cognitive “slowing” can occur as a part of the normal aging process, symptoms of dementia are distinct and are signs of disease, experts say. 

According to the National Institute on Aging, signs that you or a loved one may be experiencing dementia—and not just normal aging—include:

• Asking the same question repeatedly
• Having trouble following directions like recipes
• Getting lost in a place you know well
• Becoming increasingly more confused about time, places, and people
• Not taking care of yourself, including eating poorly, forgetting to bathe or shower, or acting in an unsafe manner

Making a bad decision, missing a monthly payment, or losing something from time to time is normal, according to the agency. But making poor decisions much of the time, having trouble taking care of your monthly bills, and misplacing things often (and being unable to find them) is not.

What to do if you’re concerned about dementia

Those with dementia symptoms should contact their doctor, who will ask questions like when the symptoms began, if they’ve been getting worse, and to what extent, if any, they’re interfering with daily activities. A doctor may choose to refer a patient for a neuropsychological exam, which could shed further light on the situation or simply provide a record of baseline cognitive functioning, experts tell Fortune.

“Everyone has a slip once in a while,” Schumann says, citing the example of a lone incident of misplaced keys. 

But symptoms like trouble balancing a checkbook and remembering how to dress and groom oneself are often signs of dementia, he cautions. The good news: If mood changes or sleep disturbances aren’t present, dementia is unlikely.

While the thought of a dementia diagnosis can be frightening, many are pushing for an early diagnosis, Reuben says. That’s for several reasons. It allows one to get their affairs in order. And it also provides a ray of hope, since there “may be drugs on the horizon” that can help those with earlier stage dementia.