Humans lose between 30,000 and 40,000 skin cells every hour. During a 24-hour period, a person loses almost a million skin cells. The human body is made up of roughly 10 trillion cells in total, 1.6 trillion of which are skin cells.
Human skin is composed of several layers, and the outer layer is called the epidermis, which is composed of cells made of keratin called keratinocytes. Keratinocytes are formed in the lower level of the epidermis, which bonds with the second skin layer called the dermis. The new skin cells slowly push their way up to the top epidermal layer, where they die. The top layer is called the stratum corneum. Eventually, the dead cells break away from the epidermis and fall off, making room for newer cells to come up from below.
It takes approximately one month for new skin cells to make their way up to the top layer. This means that the skin a person had the month before is composed of completely different skin cells from the ones he has in the current month. The dust that collects on tables, shelves, window ledges and other areas of the home is made mostly from dead human skin cells.