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Medically reviewed by Last updated on Mar 20, 2023.

What is aging?

Harvard Health Publishing

We all know the obvious signs of aging: wrinkles, gray hair, a slightly stooped posture, perhaps some "senior moments" of forgetfulness. But why do those things happen? What is aging?

Each of us is made up of cells — 13 trillion of them. Our tissues and organs are each a bunch of cells, held together with various natural materials that the cells have made.

From the moment of conception, each of our cells — and, hence, our tissues and organs — begins a process of aging. Early in life, of course, we still are growing, and expanding the number of cells that we have. The cells are aging, but so slightly that we can't see it: we just see the body growing and developing.

At some point in life, often in the 30's, the tell-tale signs of aging begin to be apparent. They can be seen in everything from our vital signs (like blood pressure) to our skin, to our bone and joints, to our cardiovascular, digestive, and nervous systems, and beyond. Some aging changes begin early in life. For example, your metabolism starts to gradually decline beginning at about age 20. Changes in your hearing, on the other hand, do not usually begin until age 50 or later.

We do not yet fully understand the complex interplay of factors that cause us to age as we do. We know that many different things affect aging: genetics, diet, exercise, illness, and a host of other factors, all of which contribute to the aging process.

A series of remarkable biological research studies since the 1990s have identified genes that can profoundly influence the rate at which cells, and animals, age. The good news from these studies is that biological changes that extend life also seem to extend vitality: animals that live longer remain quite healthy for most of their lengthened life.

None of these discoveries is close to providing a "fountain of youth" for humans, but some scientists believe that research breakthroughs regarding aging in the 21st century will lead to the development of drugs that can extend human life and simultaneously improve human health. If that happens, of course, it will only be a good thing if the world finds room, work and resources for all the additional people.

Following are examples of how aging affects some of our major body systems.

Cells, organs, and tissues:

Heart and blood vessels:

Vital signs:

Bones, muscles, joints:

Digestive system:

Brain and nervous system:

Eyes and ears:

Skin, nails, and hair:

Symptoms of aging

We each age at different rates, and to different degrees, and yet we experience many common effects of aging. Some common signs and symptoms of aging include:

Diagnosing aging

Although the body and mind go through many natural changes as we age, not all changes are normal. There are many misconceptions about what is a normal part of aging. Senility, for example, is not a natural consequence of getting old, though many people believe that it is.

It is important to talk to your physician about any changes you are experiencing. Your doctor can help you differentiate between what is a normal part of aging, and what is not. If necessary, your doctor may refer you to a specialist.

Expected duration of aging

Aging is a continuous, progressive process that continues until the end of life.

Preventing aging

We cannot change our genes, and we cannot stop the passage of time. However, through lifestyle changes, we can reduce our risk for some of the diseases and conditions that become more likely as we age. We can also prevent diseases with screening tests and immunizations.

Screening tests. Screening tests can detect diseases at early, and potentially curative, stages. However, the potential benefits of screening tests and procedures decline as you get older. Indeed, screening tests can sometimes lead to harm.  For example, if the test is falsely positive — if it indicates that a person may have a disease even when he doesn't — additional, more risky, and unnecessary, testing may be ordered.

Work with your doctor to determine whether you should have a particular screening test. For example, a screening test for a particular disease may not be necessary if your risk of getting that disease is very low in the first place. Or if you know you would not accept treatment for a particular disease, if it was discovered by a screening test, then it might not be worth getting the test in the first place. Or if it would not extend or enhance your life to discover and treat a particular disease, then it would not be worth doing a screening test for the disease. Only your health care provider and you can determine whether screening tests are worthwhile.

Immunizations. The most commonly recommended vaccines for adults include:

These are general recommendations for older adults. For some older adults, additional immunizations may be recommended. For others, such as people with weakened immune systems, some generally recommended immunizations should not be given. To sort this all out, talk with your doctor.

Treating aging

As you age, it is important to think about not only how long you will live, but how well you will live. The following strategies can help you maintain and perhaps even enhance your quality of life as you age.

When to call a professional

Call your doctor if you notice any changes that are not a normal part of aging. For example, although some occasional forgetfulness and slowing of thought are not uncommon, delirium, dementia, and severe memory loss are not a normal part of aging, and should be reported to your doctor.


Although aging is inevitable, you can take steps to reduce your risk of disease and maintain your quality of life as you get older.

Additional info

American Geriatrics Society Foundation for Health in Aging

National Institute on Aging

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.