Why Do We Have Fingernails and Toenails?

Our fingernails and toenails are essentially tough, rigid plates that protect the ends of our fingers and toes from damage, and act as a barrier to stop microbes like bacteria, fungi, and viruses entering the body and causing infections. Nails also enhance the sensitivity of the ends of the fingers and toes when they touch an object, enable us to scratch things, and make it easier for us to pick up very fine things like a hair on a jumper or a needle on the floor.

How Do Nails Grow?

Nails have several parts. The hard surface that we think of as being the actual nail is called the nail plate and is mostly made of a protein called keratin, which is also found in claws, horns, and hooves of other animals. The nail bed is a layer of skin that is visible directly under the nail plate (which is semi-transparent). At the base of the nail, a thin layer of skin called the “cuticle” grows over the nail plate and provides a waterproof barrier.

Below the cuticle is the “proximal nail fold”, which covers a pouch of skin that the nail is tucked into called the nail matrix. The whitish, half-moon-shaped area at the base of the nail is the part of the matrix that is visible. The nail matrix is the part of the nail responsible for its growth. Keratin is constantly being produced and slowly pushes the nail plate forward, causing it to grow longer. Fingernails grow faster than toenails and do so, on average, at a rate of 3–3.5 millimeters per month.

How Does Nail Integrity Represent Overall Health?

The keratin that forms the nail plate comes from a specialized type of cell. The way in which these cells link together can affect the consistency, strength, and look of the nail plate. As a result, because the nail plate forms from living cells, changes to the way the nail looks can indicate that a person has a health problem like a nutritional deficiency.

For example, people with a chronic iron deficiency may have nails that bend up at the sides or that are unusually pale, while clubbing (when nails appear swollen or wider than normal) can indicate low oxygen levels in the blood, potentially caused by a chronic lung disorder. In addition to nail abnormalities caused by underlying health problems, the nails themselves can become diseased. The nail plate is more permeable (a measure of how easily gases and liquids can pass through something) than skin, which means that harmful substances and microbes can penetrate it more easily.

What Are Some Common Nail Disorders?

There are a range of nail disorders that are caused by different things:

• Brittle nail syndrome causes the nail to become fragile.
• Onychomycosis is a fungal nail infection that can cause the nail to become brittle and discolored.
• Habit-tic nail deformity is caused by the repeated rubbing, picking, or pushing back of the proximal nail fold.
• Periungual/subungual verrucas are a type of wart that forms in the grooves of the proximal nail fold or under the nail plate.
• Nail psoriasis is an autoimmune disorder that can cause nails to become pitted and discolored, and may be accompanied by a psoriatic rash (patches of skin that are red, dry, and flaky).

What Did the Article Investigate?

Because many nail disorders are chronic conditions (lasting for a long time or that come back over and over again), there is a need for more safe, effective treatments for nail disorders that can be used long-term. Although there is limited clinical evidence that treatment with vitamin supplements can be effective, survey-based studies have shown that dermatologists (doctors that specialize in treating nail, skin, and hair problems) often recommend vitamin supplements to patients, and that self-reported use of vitamin supplements to improve nail, skin, and hair disorders among affected patients almost doubled between 2011–2012 and 2017–2020.

The authors of the article searched the published medical literature for studies that have assessed the effectiveness of vitamin and vitamin derivatives in treating nail disorders if taken by mouth (orally), applied on the outside of the body (“topically”, for example a cream that is rubbed into the skin or nail), or applied directly to lesions (areas of nail or skin damage, for example by being injected into an abnormal area of skin). In total, 49 articles were considered suitable for assessment. In addition to looking at research involving the common nail disorders described above, the authors also looked at evidence relating to a rare condition called yellow nail syndrome.

What Did the Authors Conclude?

The authors concluded that, overall, there is currently limited evidence to support treating nail disorders with vitamins and their derivatives. Exceptions to this included the treatment of some patients with yellow nail syndrome with oral or topical vitamin E, and the treatment of patients with onychomycosis with topical vitamin E (although the authors note that clinical trials are needed to investigate its efficacy and possible side effects).

The treatment of nail psoriasis with topical tazarotene, a type of retinoid (a form of vitamin A), or analogs of vitamin D (these are forms of naturally occurring vitamin D that have been chemically modified to have different or greater therapeutic effects) was evaluated as having been proven to be effective. In addition, intralesional vitamin D3 treatment seemed to be effective in treating periungual/subungual verrucas, but the authors noted that more studies are needed.

Overall, the authors did not find good evidence that taking vitamin supplements is effective in treating nail disorders. These findings confirm the fact that further research is needed to develop more effective treatments for nail disorders, and that people who develop nail disorders should seek specialist advice from a dermatologist rather than relying on taking vitamin supplements to improve the condition.