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Nail: growth, composition, scheme, diseases

 Nail: growth, composition, scheme, diseases


The nail corresponds to the horny blade that is on the dorsal end of the fingers and toes. Several parts form each nail. Nail growth, composition, role, diseases ... Deciphering the mysteries of nails.

Definition: what is a nail?

The nail is a terminal appendage, that is to say, an apparent epidermal production like hairs, feathers, scales, claws, or teeth. It is produced above the last phalanx, in the nail matrix located under the skin. This matrix is ​​a place of multiplication of cells that take care of keratin and provide the solid structure of the nail. The nail forms an additional protective layer for the skin which, in this area, is very thin and can be useful in case of defense against scratches.

Anatomy and composition


  • Basically, the matrix produces a protein called keratin.
  • The eponychium commonly called the cuticle, which covers the matrix.
  • The lunula is distinguished by its whitened color at the base of the nail.
  • The hyponychium, paronychium, and the nail bed complete this anatomy.

Nail growth

Mainly composed of keratin, the nails form horn blades located on the dorsal ends of each finger. Conversely to hair which grows cyclically, nails have the specificity of growing continuously. The nail grows thanks to the process of keratinization of cells made by the matrix. This part of the nail, implanted at the nail base, corresponds to the site of keratin production. The nails grow relatively slowly. Estimates indicate that the fingernail grows at 3 millimeters per month compared to 1.5 millimeters per month for a toenail.

Nail shape

As with other parts of the body, the shape of the nail is genetically determined. It can be wide, narrow, square, rectangular, almond, or triangle.

Role: what is the nail for?

Nails are a heritage from our ancestors which protect the fingertip from various chemical, biological and mechanical traumas. They contribute to tactile discrimination and fine motor ability of the fingertips and toes. Incidentally, they are also useful for scratching and defending themselves.

Nail problems: what it means

Nail diseases are called onychopathies:

  • Onychophagia, which refers to the irrepressible need to bite your nails.
  • The ingrown nail, that is to say, the nail that digs into the skin.

Ingrown toenail: how to treat it?


An ingrown toenail occurs when the edge of a fingernail pushes into the flesh around the nail and causes a painful or even infected lesion. What to do at the first pain? How to prevent an ingrown toenail?

  • Onychomycosis (or nail fungus): infectious pathology due to the presence of a parasitic fungus called dermatophyte. It causes thickening of the nail, discoloration, flaking, or even a slowdown in growth. 

Nail fungus (foot, hand): recognize and treat onychomycosis

Nail fungus or "onychomycosis" affects 6 to 9% of the population, mainly adults and particularly in the feet. They must be treated quickly to prevent their spread to other parts of the body ...


  • Onychodystrophy (or deformation of the nail): which causes disturbances in the growth of the nails, with a chewed nail effect that can change color towards white or yellowish.
  • Digital hippocratism: which most often reveals lung disease (tuberculosis, cancer, cystic fibrosis). The nails are more rounded and begin to take the form of spatulas.
  • Onychogryphosis (claw nail) and pachyonychia: These are enlarged nails that often follow eczema, psoriasis, mycosis, or trauma suffered by the nail.
  • The nails thicken, harden, lengthen and curl. They take on a greenish or grayish color.
  • Pinch nail disease: pathology inherited or caused by a primary disease such as psoriasis, yeast infection, nail tumor, cyst, or colon cancer.
  • Onychoptosis: a disease caused by a yeast infection, psoriasis, or severe shock. The nail comes loose from its bed.
  • Onycholysis: is characterized by the gradual detachment of the nail from its bed and this from the free edge. It can be caused by too aggressive a manicure, the use of very corrosive chemicals, or a disease such as psoriasis, lupus erythematosus, eczema, or cancer.

Nail color

The nail can take on different colors depending on the environment or the person's state of health:

  • Yellow nail (s) can be caused by a yeast infection, taking certain medications, nicotine in smokers, using chemicals without gloves.
  • A nail (s) with brown or black spots or bands on the nail bed may be caused by melanocytes (melanonychia) due to vitamin B12 deficiency, trauma to the nail, or onychophagia.

Find out more:

Yellow, blue, cracked nail: what do these symptoms mean?


Is one or more of your nails yellow, blue, black, streaked, or cracked? Is it a trauma? From a yeast infection? Psoriasis? The decryption of the symptoms and causes of nail diseases with Dr. Marie-Estelle Roux, the dermatologist.

How to take care of your nails?

To take care of your nails and limit the risk of infection, it is better to file them in one direction rather than cutting them with nail clippers. We also recommend moisturizing the cuticles with an oil or cream before gently pushing them with a cuticle regrowth. In the case of the yellowed nails, it is possible to reduce the color by rubbing the tips of the nails with lemon to whiten them. To avoid breaking them, it is best to cut them regularly without waiting for them to be too long. Consulting a podiatrist can be helpful for more delicate toenail trimming. In the case of pathology, it is recommended to consult the attending physician and possibly a dermatologist to find the cause and the necessary treatment.

Biting your nails: how to stop?

Onychophagia is a minor mania but it can lead to local infections. To get rid of it, it is recommended to practice physical activities to relieve stress such as taking care of the hands, or chewing gum for example. The will is enough in the vast majority of cases.

Biting your nails (onychophagia): how to stop?


The action of biting the nails or "onychophagia" is a frequent behavior in pre-adolescents, even if it can affect children from the age of 3 years and some adults. This mania is usually related to stress, boredom, or intense concentration. Tips for quitting.

My advice

If you want to put varnish on your nails, do not forget to apply a base coat to protect the nails (and prevent them from turning yellow with the application, for example).