Most cases of Alzheimer’s disease don’t have a clear cause. Genes and the environment can raise risk, but researchers still don’t fully understand why some people develop Alzheimer’s and others don’t. What they do know is that understanding risk factors may help people make healthier choices to support brain health — though these steps cannot prevent Alzheimer’s.

Risk Factors for Alzheimer’s

Although science is good at finding correlations — apparent relationships — between factors and disease, correlation does not prove that the factor causes the disease. Many risk factors for Alzheimer’s have been identified and are being studied, but none have been pinpointed as the cause of Alzheimer’s. Below are some of the main risk factors scientists have identified that may raise the chances of developing Alzheimer’s disease.

1. Age

Age is the most important factor for the development of Alzheimer’s. It’s typically diagnosed after age 65. It is estimated that one-tenth of people age 65 or older and one-third of people age 85 or older have Alzheimer’s.

2. Genetic Factors

Having a close family member with Alzheimer’s increases the risk of developing the condition. However, a family history isn’t a guarantee of Alzheimer’s, and plenty of people develop the disease without a family history. The majority of Alzheimer’s cases are not inherited in a simple, predictable way. For most, a combination of multiple genes and lifestyle factors contributes to risk.

Scientists have identified more than 100 genes that could make someone more likely to develop Alzheimer’s. APOE-e4 is the most common and well-identified gene that’s linked to Alzheimer’s disease. Between 40 percent and 65 percent of people with Alzheimer’s have at least one copy of this gene. Having this gene is not a guarantee that you will develop Alzheimer’s disease, nor does a lack of it mean you are immune. Many people with the APOE-e4 gene never develop Alzheimer’s, and many who do have Alzheimer’s do not have this gene.

In less than 1 percent of cases, Alzheimer’s is caused by rare genes passed down directly from a parent. This type of Alzheimer’s disease, called familial Alzheimer’s disease (FAD), runs in specific families. People with FAD usually start showing symptoms earlier, often in their 40s and 50s, instead of later in life.

People with Down syndrome are at a higher risk of developing Alzheimer’s disease. Alzheimer’s is linked to the extra chromosome 21 that causes Down syndrome. This chromosome contains the gene for amyloid precursor protein, a key protein involved in making the amyloid plaques characteristic of Alzheimer’s disease. Memory loss and other dementia symptoms typically start earlier for someone with Down syndrome.

3. Sex

According to the Alzheimer’s Foundation, women are more likely than men to develop Alzheimer’s. About 2 in 3 people with Alzheimer’s are women. Women have a higher risk of Alzheimer’s partially because they live longer, and the risk of Alzheimer’s increases with age. Researchers are investigating other potential factors, including hormonal changes after menopause and different biological mechanisms, to fully understand why women are at a higher risk.

4. Ethnicity

Ethnicity may play a role in Alzheimer’s risk. The Alzheimer’s Association reports that older Latinos are about 1.5 times more likely to develop Alzheimer’s or other types of dementia compared with older white adults. Older African Americans are about twice as likely.

Even though these groups are more likely to develop Alzheimer’s or another kind of dementia, they are diagnosed less often than white older adults. This gap is troubling, as it can delay access to care, treatment, and support.

Some research shows that higher rates of diabetes or high blood pressure are a factor in higher Alzheimer’s rates among Latino and African American populations in the U.S.

5. Environmental Factors

Factors like your physical environment, accidents, and illnesses you may be exposed to can affect your risk of Alzheimer’s.

Several studies have found a link between traumatic brain injuries and a higher risk of Alzheimer’s. Simple safety steps, like wearing a helmet when biking or buckling your seat belt, can help protect your head and lower that risk.

Air pollution has been linked to dementia risk. More research is needed to fully understand this relationship. Some studies suggest that breathing polluted air over many years may speed up changes in the brain related to Alzheimer’s.

Infections like herpes, pneumonia, and syphilis are associated with Alzheimer’s and other forms of dementia, though the exact relationship is still under investigation. A 2025 study suggested that human herpes simplex virus-1 (HSV-1) may play a role in Alzheimer’s by setting off brain changes linked to protein buildup and inflammation — and some antiviral drugs may help reduce these effects. However, having HSV-1 does not mean a person will develop Alzheimer’s.

6. Other Health Conditions

Your brain health and your heart health are connected. Conditions like high blood pressure, high cholesterol, and type 2 diabetes, especially if not well managed, are linked to Alzheimer’s disease. This is why working with your doctor to control these conditions is so important for your overall health.

Untreated hearing loss is another risk factor. Hearing aids are important for improving your hearing and for protecting against dementia. They keep your brain engaged by making it easier to follow conversations and stay socially connected, which supports brain health.

There is emerging research that untreated vision loss could also influence your risk of Alzheimer’s, possibly because it makes the brain work harder, limits social engagement, or is tied to other health problems like diabetes.

7. Lifestyle Factors

Many health conditions that can increase Alzheimer’s risk are influenced by lifestyle. Habits like smoking, not getting much physicial activity, and eating a diet high in calories, fat, carbs, and salt can add to the risk of Alzheimer’s.

The good news is that adopting healthy habits — such as quitting smoking, staying physically active, and eating a balanced diet — is one of the most powerful steps you can take to reduce your risk.

What Does Not Cause Alzheimer’s?

Many substances and objects were thought at one time to increase the risk of developing Alzheimer’s. The following have been thoroughly studied as potential risk factors, and no link with Alzheimer’s has ever been proved:

• Aluminum (in deodorants, cooking pans, beverage cans, etc.)
• Flu shots and other vaccinations
• Dental fillings made with an amalgam of silver and mercury

Ask Your Doctor About Your Risk

Scientists don’t yet know exactly what causes Alzheimer’s, but research shows that a mix of age, genetics, health conditions, and lifestyle all play a part in shaping risk. While you can’t change your genes or age, you can take steps to support your brain — from staying active and eating well to protecting your hearing, vision, and heart health. Learning about these risk factors is helpful because it shows there are choices you can make today that may help protect your memory and overall brain health.

Join the Conversation

On myALZteam, people share their experiences with Alzheimer’s disease, get advice, and find support from others who understand.

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