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Medically reviewed by Last updated on Jan 25, 2022.

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 1990's 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: 

  • Cells become less able to divide 

  • The telomeres—the ends of the chromosomes inside every cell—gradually get shorter until, finally, they get so short that the cell dies 

  • Waste products accumulate  

  • Connective tissue between the cells becomes stiffer 

  • The maximum functional capacity of many organs decreases

Heart and blood vessels:

  • The wall of the heart gets thicker 

  • Heart muscle become less efficient (working harder to pump the same amount of blood) 

  • The aorta (the body's main artery) becomes thicker, stiffer, and less flexible 

  • Many of the body's arteries, including arteries supplying blood to the heart and brain, slowly develop atherosclerosis, although the condition never becomes severe in some people

Vital signs:

  • It is harder for the body to control its temperature 

  • Heart rate takes longer to return to normal after exercise

Bones, muscles, joints:

  • Bones become thinner and less strong 

  • Joints become stiffer and less flexible 

  • The cartilage and bone in joints starts to weaken 

  • Muscle tissue becomes less bulky and less strong

Digestive system:

  • The movement of food through the digestive system becomes slower 

  • The stomach, liver, pancreas, and small intestine make smaller amounts of digestive juices

Brain and nervous system:

  • The number of nerve cells in the brain and spinal cord decreases.  

  • The number of connections between nerve cells decreases 

  • Abnormal structures, known as plaques and tangles, may form in the brain.

Eyes and Ears:

  • The retinas get thinner, the irises get stiffer 

  • The lenses become less clear 

  • The walls of the ear canal get thinner 

  • The eardrums get thicker

Skin, nails, and hair:

  • Skin gets thinner and becomes less elastic 

  • Sweat glands produce less sweat 

  • Nails grow more slowly 

  • Hairs get gray and some no longer grow


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:

  • Increased susceptibility to infection 

  • Greater risk of heat stroke or hypothermia 

  • Slight decrease in height as the bones of our spines get thinner and lose some height 

  • Bones break more easily 

  • Joint changes, ranging from minor stiffness to severe arthritis 

  • Stooped posture 

  • Slowed and limited movement 

  • Decrease in overall energy 

  • Constipation 

  • Urinary incontinence 

  • Slight slowing of thought, memory, and thinking (however, delirium, dementia, and severe memory loss are NOT a normal part of aging) 

  • Reduced reflexes and coordination and difficulty with balance 

  • Decrease in visual acuity 

  • Diminished peripheral vision 

  • Some degree of hearing loss 

  • Wrinkling and sagging skin 

  • Whitening or graying of hair 

  • Weight loss, after age 55 in men and after age 65 in women, in part due to loss of muscle tissue. 


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

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


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: 

  • Influenza, every year 

  • Pneumococcal pneumonia vaccination (series of two vaccines) for people ages 65 and over, and those in the 19-64 age range and at risk for pneumococcal infection (such as from chronic heart or lung disease) 

  • Tetanus, diphtheria and pertussis (one shot on at least one occasion), and then tetanus and diphtheria every 10 years 

  • Herpes zoster (shingles) vaccine for people ages 60 and over, even if they have had an attack of shingles earlier in life; 

  • Meningococcal vaccine if you are at particular risk for this condition (talk to your doctor); 

  • Human papillomavirus vaccine if your are age 19-26 (men who get the vaccine at age 19-21 need it again in the 22-26 age range, if they are at special risk for this infection, such as by having sex with men); 

  • Hepatitis A virus and hepatitis B virus vaccines, if you did not get them as a child, and if you are a particular risk for this infection; 

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.


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.

  • Don't smoke. Smoking contributes to heart disease, osteoporosis, and stroke, and it increases the risk of many cancers. Smoking even appears to make a person's memory worse. The good news is that people who quit smoking can repair some, if not all, of the damage done by years of smoking.  

  • Build physical and mental activities into every day. Physical activity is good for the body and the mind. Exercise (and even activity such as gardening or housekeeping that people don't think of as exercise) helps keep your bones and heart healthy, and your weight in check. Studies have also shown that physically active people lower their risk for developing dementia and are more likely to stay mentally active. And staying mentally active helps ward off memory loss. 

  • Eat a healthy diet rich in whole grains, vegetables, and fruits, and substitute healthier monounsaturated and polyunsaturated fats for unhealthy saturated fats.  Such a diet protects you against many diseases, including the biggest killers—heart disease, cancer and stroke. 

  • Maintain a healthy weight and body shape. As we get older, our metabolism slows, making it harder to burn off calories. But excess body weight can increase the risk of heart disease, diabetes, stroke, and certain cancers. Body shape is important as well. Men and women who carry more weight around their abdomens have a higher risk of heart attack and stroke than those who carry extra weight around their hips. 

  • Challenge your mind. Some evidence suggests that reading, doing crossword puzzles, playing a musical instrument, even engaging in thought-provoking conversations, can help keep your mind sharp.  

  • Build a strong social network. As you get older, it's important to maintain close and rewarding ties with family and friends, and to create new connections when possible. Some studies suggest that social ties might help ward off dementia and keep you mentally sharp. Other studies suggest that strong social connections can help you live longer. 

  • Protect your sight, hearing, and general health by following preventive care guidelines. 

  • Floss, brush, and see a dentist regularly. Poor oral health may have many repercussions, including poor nutrition, unnecessary pain, and possibly even a higher risk of heart disease and stroke. 

  • Discuss with your doctor whether you need any medication — perhaps to control high blood pressure, treat osteoporosis, or lower cholesterol — to help you stay healthy. 

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.

External resources

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.