How many cells are in the human body?
An average adult human body contains roughly 30 to 37 trillion human cells. Studies estimate a similar number of bacteria also live in and on the body, mostly in the gut.
Counting every cell directly is impossible, so scientists estimate by measuring the number of cells in each type of tissue. A widely cited 2013 study put the total at about 37 trillion. A 2016 analysis estimated about 30 trillion human cells in a typical man, and a 2023 study estimated around 36 trillion for men and 28 trillion for women.
Red blood cells make up the vast majority of these cells, around 25 trillion, even though each one is tiny. Fat cells and muscle cells are much larger, so they make up most of the body's mass despite being far fewer in number. There are about 200 main types of cells in the body.
Constant renewal
Your body replaces millions of cells every second. Cells lining the gut are replaced every few days, red blood cells last about 120 days, and skin cells are constantly shed. Some cells, such as most neurons in the brain and the cells in the lens of the eye, can last a lifetime.
Did You Know?
Bacteria cells are much smaller than human cells, so even though there are about as many of them, together they weigh only around 0.2 kilograms.
This answer is general information, not medical advice. For a personal health question, talk to a doctor.