6.1 Nail Structure, Growth, and Anatomy
Key Takeaways
- The technical term for the natural nail is onyx, which is composed of hard keratin and has a normal water content of 15% to 25%.
- A healthy nail grows forward from the matrix, with an average growth rate of 1/10 to 1/8 inch (2.5 to 3.0 mm) per month.
- The fingernail takes approximately 4 to 6 months to fully replace itself, whereas a toenail takes 9 to 12 months.
- Under Florida cosmetology rules, cosmetologists are strictly prohibited from cutting the living eponychium; only dead cuticle tissue may be removed.
- Specialized ligaments attach the nail bed and matrix to the underlying bone, securing the nail unit in place.
6.1 Nail Structure, Growth, and Anatomy
The technical term for the natural nail is the onyx. The natural nail is an appendage of the skin and is part of the integumentary system, which includes the skin, hair, and glands. A healthy natural nail is firm but flexible, shiny, and slightly pink in color. The surface of a healthy nail is smooth and unspotted, without any deep ridges, pits, or splits. To provide professional, safe, and effective nail services, a cosmetologist must possess a deep understanding of nail anatomy, the chemical composition of the nail, and the factors that influence its growth and regeneration.
Chemical Composition of the Natural Nail
The natural nail is composed mainly of a protein called keratin, which is the same fibrous protein found in the skin and hair. However, the keratin in nails is harder than the keratin found in hair or skin due to its molecular structure and lower water content.
A healthy nail contains between 15% and 25% water. The water content directly affects the nail's flexibility. If the water content falls below 15%, the nail becomes brittle and prone to breaking or splitting. If the water content is too high (above 25%), the nail becomes overly soft and flexible. Applying an oil-based conditioner or nail cream reduces water loss and helps maintain the ideal balance of moisture, preserving flexibility.
Anatomy of the Nail Unit
The natural nail is not a single structure but is composed of several major parts that function together. Collectively, these parts are referred to as the nail unit.
| Anatomical Structure | Description | Living or Non-living | Primary Function |
|---|---|---|---|
| Nail Plate | Hard keratin plate covering the nail bed | Non-living | Protects the sensitive nail bed beneath |
| Nail Bed | Living skin supporting the nail plate | Living | Guides and supports the plate as it grows |
| Matrix | Area where nail plate cells are formed | Living | Produces new cells for nail plate growth |
| Cuticle | Dead, colorless tissue on the nail plate | Non-living | Seals the space between plate and eponychium |
| Eponychium | Living skin at the base of the nail plate | Living | Protects the matrix from pathogens |
| Hyponychium | Skin under the free edge of the nail | Living | Prevents dirt and bacteria from entering the nail bed |
| Specialized Ligaments | Fibrous tissue connecting bed/matrix to bone | Living | Anchors the nail unit to the underlying bone |
| Nail Folds | Folds of skin surrounding the nail plate | Living | Protects the sides of the nail and forms grooves |
The Nail Plate
The nail plate is the most visible and functional part of the nail unit. It is constructed of approximately 100 layers of flattened, dead nail cells. The nail plate is relatively porous, meaning it can absorb water and other liquids, which is why nail polishes and artificial enhancements can adhere to it. The part of the nail plate that extends over the tip of the finger or toe is called the free edge.
The Nail Bed
The nail bed is the portion of living skin that supports the nail plate as it grows toward the free edge. Because it is alive, the nail bed is highly sensitive and contains many nerves, lymph vessels, and blood vessels, which give the nail its healthy pinkish color. The nail bed is attached to the nail plate by a thin layer of tissue called the bed epithelium, which guides the nail plate along the nail bed as it grows.
The Matrix
The matrix is the active, living area where the nail plate cells are formed. It contains nerves, lymph vessels, and blood vessels to nourish the developing cells. The matrix extends from under the eponychium and lies hidden beneath the nail fold at the base of the nail. The visible part of the matrix that extends from underneath the living skin is the lunula, the whitish, half-moon shape at the base of the nail. The lighter color of the lunula is caused by the reflection of light where the matrix and connective tissue meet. A healthy, undamaged matrix is absolutely essential for the growth of a normal nail plate.
The Cuticle
The cuticle is the dead, colorless tissue attached to the natural nail plate. It comes from the underside of the skin fold surrounding the nail plate. The cuticle is incredibly sticky and adheres tightly to the nail plate, making it difficult to remove. Its primary function is to seal the space between the natural nail plate and the surrounding living skin (eponychium), preventing entry of foreign material and microorganisms.
The Eponychium
The eponychium is the living skin at the base of the natural nail plate covering the matrix area. It is frequently confused with the cuticle, but they are anatomically distinct. The eponychium is living tissue, whereas the cuticle is dead tissue.
[!IMPORTANT] Under Florida DBPR rules and standard cosmetology practice, cosmetologists are strictly prohibited from cutting the eponychium or any other living skin. Only dead tissue, such as the cuticle, may be gently pushed back or nipped if loose. Cutting living skin can lead to severe infections, scarring, and permanent damage to the matrix.
The Hyponychium
The hyponychium is the slightly thickened layer of skin that lies between the fingertip and the free edge of the nail plate. It forms a protective barrier that prevents dirt, water, and microorganisms from invading and infecting the nail bed. Damaging the hyponychium can cause the nail plate to separate from the nail bed.
Specialized Ligaments
A ligament is a tough band of fibrous tissue that connects bones or holds an organ in place. In the nail unit, specialized ligaments attach the nail bed and matrix bed to the underlying bone of the fingertip. These ligaments are located at the base and sides of the nail unit, securing it firmly in place and stabilizing the nail as it performs daily tasks.
Nail Folds and Grooves
The nail folds are folds of normal skin that surround the nail plate. These folds form the nail grooves, which are the slits or furrows on the sides of the nail. The nail plate slides along these grooves as it grows. The fold of skin that overlaps the side of the nail is also referred to as the 'lateral nail fold' or sidewall.
Nail Growth and Regeneration
Nail growth is affected by nutrition, general health, and aging. The growth of the nail plate is direct and continuous, occurring in a forward direction from the matrix toward the free edge.
Nail Growth Rate
The average rate of nail plate growth in a normal adult is approximately 1/10 to 1/8 inch (2.5 to 3.0 millimeters) per month. However, this rate is not constant and varies based on several factors:
- Age: Nails grow fastest in children and slow down as a person ages.
- Seasons: Nails grow faster in the summer than in the winter.
- Finger Position: Nails on the middle finger grow the fastest, while the thumb nail grows the slowest. Fingernails grow much faster than toenails.
- Pregnancy: Hormonal changes during pregnancy significantly increase the nail growth rate, particularly during the second and third trimesters, but the rate returns to normal quickly after delivery.
Regeneration and Replacement
Because the nail plate is composed of non-living cells, it cannot heal itself if damaged. If the nail plate is lost due to injury or disease, it will regenerate as long as the matrix remains healthy and undamaged.
- A complete replacement of a fingernail takes approximately 4 to 6 months.
- A complete replacement of a toenail takes approximately 9 to 12 months.
If the matrix is severely injured, bruised, or infected, the new nail plate may grow back deformed, ridged, or it may not grow back at all. Cosmetologists must handle the matrix area with extreme care during all nail services.
What is the average rate of fingernail growth per month in a normal adult?
Which anatomical structure is the dead, colorless tissue that adheres tightly to the natural nail plate and must be removed during a manicure?
If a client loses a fingernail due to trauma, how long does it typically take for the fingernail to be completely replaced?