Thick Fingernails – Anatomy (Parts) and Causes

Our fingernails are tough, waterproof structures that are made up of a protein known as keratin. They are similar to the claws found in many animals. We see the nails as continuous, thin plates of inert keratin that lie at the edges of our fingers, and usually do not give them any further thought. However, the condition of our nails could indicate underlying health problems. In order to decipher whether our nails are abnormal, we first need to understand the normal nail structure.

Fingernail Anatomy

The fingernail that we see is also known as the nail plate. The nail plate is a translucent structure made up of keratin. It appears pinkish in color due to the capillaries that lie in the skin located below the fingernail. The skin below the fingernail is known as the nail bed, and is composed of two parts: dermis and epidermis. The cells that form the nail are produced at the nail matrix, which sits under the skin at the base of the nail plate where the nail emerges from the skin.

The nail matrix is rich in blood vessels, nerves, and lymphatic vessels. The new nail plate cells produced at the nail matrix push the older nail plate cells forward, resulting in the growth of our fingernails. The older nail plate cells that get pushed forward become flat and translucent. A part of the nail matrix is visible as a crescent-shaped whitish area known as the lunula. The lunula is most prominent in the thumbs.

The nail plate is surrounded by folds of skin on three sides, leaving only the distal edge free to grow. The distal edge of the nail plate grows out over the edge of the skin at the fingertips. The epithelium located at the junction of the distal edge of the nail and the skin on the fingertip is known as the hyponychium. The hyponychium protects the nail bed by forming a tight seal at the distal edge of the fingernail.

The seal between the nail plate and the hyponychium is known as the onychodermal band. At the proximal end of the nail plate, the epithelium that extends from the posterior nail wall onto the base of the nail plate is known as the eponychium. The eponychium produces a semi-circular layer of dead cells, known as the cuticle. Together, the cuticle and the eponychium seal the proximal end of the nail plate. The border tissue around the nail plate is known as the paronychium.

Why do the fingernails thicken?

Changes in the structure and appearance of nails could happen due to a variety of reasons. Some of the causes are natural age-related changes. However, some causes indicate the presence of an underlying disease or disorder. A thickening or overgrowth of the fingernails may or may not occur in conjunction with other fingernail abnormalities and finger deformities.

Read more on abnormal fingernails.

Causes of Thick Fingernails

The following are some of the reasons for the thickening of fingernails but there may be other less common causes that have not been discussed below.


The character of our fingernails changes with age. Both the growth rate and the morphology of the fingernails change with advancing age. Changes in the nail plate commonly seen with aging include changes in nail thickness, color, and surface features. For example, the thickness of the nail plate may either increase or decrease with age. It is also possible that the nail thickness does not change at all.

Longitudinal ridges may appear on the surface of the nail plate. The surface texture of the nail plate may lose its smoothness, and fissures and cracks may start appearing. There may also be yellow or gray discoloration of the nail color. The nail plate may also lose its translucent character and become opaque. These are normal physiological changes due to the aging process, and do not necessarily represent a pathological change or disease. However, certain diseases do cause similar changes in the fingernail structure.

Therefore, it is advisable to test for other disease conditions even when age-related fingernail thickening is suspected. It is important to rule out disease as the cause of fingernail thickening in the elderly because some diseases could result in serious consequences if prompt medical treatment is not given.


Onychogryphosis is also known with the descriptive name, “ram’s horn nails”. This name is an apt description for this condition, which is characterized by an abnormal thickening of the nails that make them crooked and similar in appearance to ram’s horns or claws. Onychogryphosis is most frequently caused by ill-fitting footwear and a failure to cut nails over a long period of time.

Physical trauma and peripheral vascular disease could also contribute to the development of onychogryphosis. This condition is most commonly seen to affect the elderly population. It is possible that an individual’s genes also contribute to the development of onychogryphosis. Congenital onychogryphosis has been observed to run in some families.

Pachyonychia congenita

Thick fingernails are also seen in a rare skin disorder with excessive keratin production known as pachyonychia congenita. This is a genetic disorder that is autosomal dominant in nature. In other words, only one defective copy of the keratin gene is enough to cause this condition. A family history of the disease may or may not be present in an affected individual’s case.

Pachyonychia congenita is characterized by excessive production of keratin, which results in a thickening of the nails. Thick fingernails in this condition are mostly seen right from the time of birth. However, in some cases, thickening of fingernails may begin a few months after birth. Excessive keratin production and thickening of nails in pachyonychia congenita affect both fingers and toes.


Nail clubbing, or digital clubbing, refers to a condition in which the nails and the distal ends of the fingers become deformed. The curvature of nails and distal ends of fingers increases along the lateral margins, making them appear bulbous. The extent of deformity ranges from very mild (hardly detectable) to grossly visible. The exact cause of nail or digital clubbing is not clear. However, some serious conditions of the lungs, heart, and gastrointestinal tract have been associated with many cases of digital clubbing.


Onychauxis refers to a thickening of nails without any other associated deformity. Onychauxis may occur in a variety of conditions, such as psoriasis, eczema, peripheral vascular disease, yellow nail syndrome, fungal infections (onychomycosis), and acromegaly.

Read more on brown fingernails.

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