From the Guidelines
Nails grow upwards due to the structure and function of the nail matrix, which is located beneath the cuticle at the base of your nail. The nail matrix contains rapidly dividing cells that produce keratin, the protein that makes up your nails. As new cells form in the matrix, they push older cells forward and upward, creating the visible nail plate. The nail bed, which lies beneath the nail plate, provides a firm foundation that guides the nail's growth in an upward and outward direction. The nail fold, the skin that surrounds the sides and base of the nail, creates a channel that further directs growth upward rather than sideways. This upward growth pattern is beneficial as it protects the nail matrix and allows the nail to serve its purpose of protecting fingertips while enabling precise manipulation of objects. Maintaining healthy nail growth requires adequate nutrition, particularly proteins, biotin, and minerals like zinc and iron, along with proper nail care to prevent damage to the matrix and surrounding structures. Some studies have investigated the effects of various factors on nail growth, including chemotherapy agents such as taxanes, which can cause nail changes and onycholysis 1. However, these factors do not affect the fundamental direction of nail growth, which is determined by the anatomy of the nail matrix and surrounding tissues. Proper care and nutrition are essential to support healthy nail growth and prevent damage to the nail and surrounding tissues 1.
From the Research
Nail Growth Direction
- The direction of nail growth is determined by the structure of the nail apparatus, which includes the matrix epithelium, nail bed epithelium, and the proximal and lateral nail folds 2.
- The nail grows outwards instead of upwards due to the shape and size of the bone of the terminal phalanx, which influences the size and shape of the nail 3.
- The proximal nail fold covers most of the matrix and forms a frame on three sides, giving the nail stability and allowing it to grow outwards 3.
Factors Influencing Nail Growth
- Nail growth is not hormone-dependent and occurs continuously throughout life at a rate of approximately 0.1 mm/day for fingernails and 0.03-0.05 mm/day for toenails 3.
- Biotin, a water-soluble vitamin, plays a crucial role in various metabolic reactions and is essential for normal human health, growth, and development, including nail growth 4, 5, 6.
- Biotin deficiency can lead to dermatological abnormalities, including nail disorders, and can be caused by insufficient dietary intake, drug-vitamin interactions, or decreased activities of proteins involved in biotin homeostasis 4, 6.