The nail anatomy is like a map of your nails. There are parts that will bleed when you cut or over file and parts that can be trimmed and will not hurt when cut. So you basically need to know which area you can work on and how to do it correctly.

Definitions

Ep-o-ny-chi-um (living tissue - cannot cut)

The area of living skin that borders the base of the nail plate and usually covers all of the nail matrix, except the lunula.

Cu-ti-cle (hardened, dry skin - can cut)

The thin layer of colorless dead tissue between the eponychium and the nail plate that forms a seal to keep dirt and debris from harming the matrix area.

Hy-po-ny-chi-um (living tissue - don't file too short or tear when cleaning)

The hyponychium is the tissue under the free edge of the nail that seals the nail plate to the tip of the finger. This is a seal to prevent pathogenic bacteria from entering the finger. Do not file the nail too short or accidentally dig too deep while cleaning the undersides of the nail as it will bleed if torn.

Nail Matrix (most important unit - nail root)

This is the root of the nail, it is not visible and protected by proximal nail fold. The matrix produces keratin cells that makes up the nail plate. Damage to the matrix can cause permanent damage to the appearance of the nail.

Lu-nu-la (also known as half moon)

Lunula is the visible part of the matrix and should be treated with care as the cells have not fully keratinised. It is white in color and opaque and resembles a half moon.

Nail Plate (non living - keratinised - free edge - can cut)

The nail plate is what we class as a "nail". These cells are not living, they are keratinised. The pink part comes from the blood vessels underneath the nail. The nail plate itself is translucent. The purpose of the nail plate is to protect the living nail bed underneath. What grows beyond the nail bed is called the free edge (what we call "nail growth") and we can cut/file this.

Nail Bed (living tissue)

The nail bed is located under the nail plate. It is made up of dermis and epidermis and contain thousands of blood vessels that carry food, oxygen and nutrients to the fingernail.

The Nail Folds (Lateral & Proximal) (living tissue)

The nail folds protect the nail matrix and are part of our skin as a protective barrier against bacteria and dirt that is common within our environment.