Structure and Growth of Fingernails and Toenails

The parts of the nail, whether at your fingers or toes, follow a basic structure. This nail anatomy serves to protect against infections or injury, while adding functional ability (like scratching) and improving sensation and dexterity (self-defense and other skill with your hands).

The structure is divided into three main parts: the nail itself, the underlying structure that supports nail growth, and the skin tissue that surrounds it.

This article explains each of these features of nail anatomy. It also discusses certain conditions that affect the health of your nails and those for which nail changes can be a sometimes surprising sign, such as liver or kidney failure.

Nail Anatomy

The nail structure is divided into different components that make up the nail itself, or the surrounding skin and structure. Each of the elements has a specific function, and if disrupted, it can affect the nail's appearance and health.

Parts of the Nail

Your nail plate is the actual fingernail, and it's made of translucent keratin. Keratin is a protein found in your nails, hair, and skin, that works to protect against infection (among other things). The pinkish appearance of the nail comes from blood vessels that are underneath it.

The underside of the nail plate has grooves that run along the length of the nail and help anchor it to the nail bed, while the free edge is the part of the nail plate extending from the finger (the white tip that you trim).

Part of the nail root appears as a visible white crescent, known as the lunula. The root portion at the base of your nail lies below the skin, underneath the nail, and extends several millimeters into the finger. It produces most of the volume of the nail and the nail bed.

The germinal matrix (the nail matrix) and the nail root are related. The matrix lies beneath the skin, at the inner edge of the nail plate, and is responsible for most of a nail's growth. It's where new cells grow and then advance forward to form the nail, until it reaches the outer edge and ultimately is removed. Without it, no nail plate growth is possible.

Underlying Structures

The nail bed is also referred to as the sterile matrix. It extends from the edge of the nail root, or lunula, to the tissue known as hyponychium.

The nail bed contains blood vessels, nerves, and melanocytes that produce melanin. As the root grows, the nail streams down along the nail bed and adds material to the underside of the nail to make it thicker. When the nail grows properly, the nail bed is smooth, but if the nail doesn't grow correctly, the nail may split or develop ridges that may be considered cosmetically unattractive.

Surrounding Tissues

The eponychium tissue produces the cuticle. The cuticle is found between the skin of the finger and the nail plate. It fuses these structures together and provides a waterproof barrier. It includes the proximal (nearest to your body) fold of the skin, at the cuticle.

The paronychium is the skin that overlaps onto the sides of the nail plate, also known as the paronychial edge of the lateral fold. The paronychium is the site of conditions including hangnails, ingrown nails, and paronychia, a skin infection.

The hyponychium is the area between the free edge of the nail plate and the skin of the fingertip. It also provides a waterproof barrier.

How Do Nails Grow?

About 80% of your fingernail arises from the nail root (which determines length) and the other 20% comes from the nail bed (which determines thickness). On average, a healthy person's fingernails grow about 3 to 3.5 millimeters per month.

Nails are constantly growing, but their growth rate slows down due to poor circulation and aging. The rate of growth also varies between its fingers and toes, and even between your different fingers.

Nail Functions

Fingernails serve a number of helpful functions, whether helping people to grip an item, used for scratching or grooming, or as a part of self-defense. For example, the DNA collected from fingernails when used to fight off an attack can be presented as evidence within the criminal justice system.

Nails aren't merely tools, with their presence boosting the ability to handle objects or feel pressure. They also serve to protect against infection, which can occur when the nail plate and other structures are damaged or brittle.

Conditions That Affect the Nails

There are a number of health conditions that can affect your nails, and in some cases (like chemotherapy), the treatments for certain diseases can affect your nail health.

A simple fungal infection can affect fingernails and toenails, while melanoma cancer can occur because melanocytes grow in the nail bed. Other conditions include:

• Trauma or injury
• Nail psoriasis
• Discoloration (melanonychia) that can be a sign of other illnesses

Certain other conditions, like clubbing, can be associated with lung disease or other conditions. Your nails also can provide information about digestive conditions, heart health, diabetes, or kidney function.

Summary

The structure of your fingernails and toenails is designed to provide protection and additional function to your hands and feet. The parts of the nail include the nail itself, the underlying support of the nail, and the skin tissue around it.

Fingernails and toenails can be directly affected by a number of health conditions, like fungal infections, but changes also can be signs of more serious health issues, including cancer. Contact your healthcare provider to discuss any concerns with your nails and their appearance.