These treatments heat the dermis and cause new collagen and elastin formation.

CNN: Wrinkles

There's also a device that uses radiofrequency instead of light to heat the dermis and underlying tissue to achieve mildly to moderately tighter skin.

CNN: Wrinkles

In ablative (wounding) laser resurfacing, a laser beam destroys the outer layer of skin (epidermis) and heats the underlying skin (dermis), which stimulates the growth of new collagen fibers.

CNN: Wrinkles

Mongolian spots (technically named congenital dermal melanocytosis) are flat bluish-green, gray or light brown areas where cells called melanocytes have been trapped in a layer of the skin called the dermis.

CNN: What are Mongolian spots?

Nelson's injuries destroyed all three main skin layers - the epidermis, dermis and hypodermis (the top, middle and bottom), in some places right down to the periosteum, the membrane overlying the bone.

BBC: US Army seeks new ways to treat facial skin injuries

He then wants to take moulded sheets of artificial skin to build up the intermediate layer, the dermis, before adding the outer epithelium graft employing new approaches that lift thin, 20-cell-thick slices from elsewhere on the body.

BBC: US Army seeks new ways to treat facial skin injuries