How Humans 'Molt'

[P3 Science and up: Life Cycles + P6 Science and up: Adaptation]

Some animals in the insect family are known for their four-stage life cycles, including a pupa stage where they liquify and reconstruct their body significantly to become something significantly different. Examples include maggots turning into flies, caterpillars to butterflies and so on. In that case, the adult form significantly differs from the young form.

Other animals, such as silverfish and pill bugs (which are actually land-based crustaceans) tend to have their young resemble their adult forms. For animals with carapace, this is normally achieved by periodic molting where their new shell has the elasticity to grow more than the old shell, and eventually the new shell hardens more than it can grow and giving way to a newer shell.

For fleshy animals like humans, however, this is a different story. Sadly, watching a human grow to that extent is considered tedious (you need to wait years to observe significant changes) and unethical (for good reason! nobody wants to be filmed pooping), so this is best captured from observing animals with shorter life cycles.

The skin on animals such as pigeons and humans are stretchy and flexible, and capable of layering repeatedly. As we grow, the skin grows various layers: The epidermis, the dermis and the hypodermis. Unlike shelled animals, our skins are stretchy and flexible enough to grow with us.

Eventually, the epidermis wears out, the dermis becomes the new epidermis and the hypodermis becomes the new dermis. Through this continuous layering of supple skin instead of carapace, we evolve by molting our skin procedurally, wearing it out part by part and replacing the parts we no longer need. As you might guess, dandruff (molting isolated at the scalp) and dead skin (we remove these with exfoliation) comes from this repeated process of molting.

Dandruff and dead skin don't really need to be classified as medical conditions, but that's a story for another time.