How old is human skin?

The answer depends on the layer of the skin you're referring to. Here's a breakdown:

Epidermis: This is the outermost layer of the skin, which acts as a protective barrier. The cells in the epidermis have an average lifespan of about 28 days. They are continuously shed and replaced by new cells, through a process called desquamation.

Dermis: The dermis is the thick layer beneath the epidermis. It contains blood vessels, hair follicles, sweat glands, and collagen and elastin fibers, which provide strength and elasticity to the skin. The cells in the dermis generally have longer lifespans and can last for several years.

Subcutaneous Tissue (Hypodermis): This is the deepest layer of the skin, primarily composed of fat cells. These fat cells have a relatively slow turnover rate, and some of them can persist for several decades, contributing to the skin's overall structure and cushioning effect.

So, the age of different skin layers can range from a few days for the outer layer (epidermis) to several years or decades for the cells in the deeper layers (dermis and hypodermis). Additionally, individual variations and factors such as genetics, lifestyle, and environmental exposures can influence the actual age and appearance of the skin over time.