The Human Body Replaces Itself Every 7 Years

Every seven years, we become essentially new people. That’s because in that length of time, every cell in our body has been replaced by a new cell. Individual cells have a finite life span, and when they die off they're replaced by new ones. There are between 50 and 75 trillion cells in the body, with each one having its own lifespan. When a person dies, it may take hours before the cells in the body die. Forensic investigators take advantage of this vaguely morbid fact when determining the cause and time of death of homicide victims. Red blood cells live for about four months, while white ones live on for more than a year. Skin cells live for about 2-3 weeks, but colon cells have it rough — they die off after about four days. The brain cells, however, typically last an entire lifetime because neurons in the cerebral cortex aren’t replaced when they die.