How often do nails grow?

The nail begins to form in utero from the ninth week of pregnancy (third month) and it acquires its definitive structure at the twentieth week of gestation (seventh month). Unlike hair which has a cyclical growth, the nail is a dynamic structure that remains mitotically active throughout life and its growth occurs in a linear direction from the nail's germinative matrix, thus allowing the protection and defence of the digital extremities, the grasping of objects, not to mention the aesthetic aspect.

Whether it's the hands or feet, the standard growth rate of a normal nail is on average one-tenth of a millimetre per day. The nails on the hands record an average growth of 3.47 millimetres per month, which is approximately 0.116 millimetres per day. If you lose a nail, it takes up to four to six months before it completely regenerates, from the root to the tip.

However, toenails grow at a slower rate than fingernails. The average growth rate is 1.62 millimetres per month, or approximately 0.054 millimetres per day. If you lose a toenail, its complete regrowth is estimated to take between nine and eighteen months: this is three times longer than the regrowth of a fingernail.

Why don't the nails on our hands and feet grow at the same rate?

The exact mechanisms that control the growth rate of fingernails and toenails are unknown. However, it is suggested that this difference could result from a difference in usage. Indeed, it could be due to the fact that toenails generally undergo less trauma than fingernails, thereby altering the nail growth pattern.

However, there are a number of factors that can affect this growth rate, for which your nails may grow faster or slower than the average.

• Age: The linear growth of fingernails and toenails significantly slows down with age and their appearance may change. A study published in 1980 examined the nail growth rate of a man over a 35-year period. At the age of 23, Dr. William BEAN observed that his left thumbnail was growing at a rate of 0.123 millimetres per day. By the time he reached the age of 67, this speed had dropped to 0.095 millimetres per day. A reason? It is assumed that this decline is part of a reduction in proliferation and metabolism at the organism level with age. Moreover, the decrease in blood flow with age may also explain this change in speed.

• Climate: A study from 1958 reported that nail growth tends to be slower in winter (Arctic climates) than in summer (temperate climates), the extent of which varies from one individual to another and depending on their level of exposure. Although there is little evidence as to the mechanism by which climate can influence nail growth, it has been suggested that this could be due to a slowdown in circulatory rates in a cold environment, suggesting that nail growth speed responds to circulatory changes.

• Forces exerted: The increase in forces exerted on the nail bed can also potentially alter the nail growth rate. Thus, the growth rate of the nails on the dominant hand (the one used for writing) is faster than that of the non-dominant hand, simply because it is subjected to more shocks on a daily basis. Indeed, a trauma can lead to an increase in the supply of blood and nutrients to the affected area for repair. These influxes can thus accelerate the growth of the nail.

  Similarly, the nails on the same hand do not all grow at the same rate. A 2010 study revealed that the nail on the little finger grows more slowly, while those on the longer fingers grow faster (middle finger). The growth rate differs by about 0.1 millimetres, which can be very noticeable from one finger to another.

• Infections: It has been reported that nails infected with fungi (onychomycosis) grow slower than normal, especially when the infection is severe. However, the mechanism is not entirely clear, but damage to the nail matrix and bed could contribute to this slowdown. Moreover, certain acute infections such as pneumonia or mumps can also cause a weakening of nail growth.

• Chronic Diseases: Several systemic diseases can also impact the growth of nails, as well as their shape and overall appearance. Certain diseases are characterised by an acceleration of nail growth (psoriasis, epidermolytic hyperkeratosis, hyperthyroidism, hyperpituitarism, pityriasis rubra pilaris, etc.), while others show a slowdown (peripheral neuropathies, hypothyroidism, lichen planus, relapsing polychondritis, etc.). Similarly, chronic diseases, such as diabetes or other circulatory problems, can slow down blood circulation in the nails, which weakens their growth.

• Malnutrition: Nutritional status can also influence the development of nails. Indeed, nails also require a continuous and normal supply of amino acids, minerals, and vitamins to grow healthily. However, studies have shown that deficiencies in micronutrients (iron, silicon, zinc, vitamin B, etc.) can affect nail growth.

• Hormone Levels: Pregnant women also experience accelerated nail growth, which decreases during breastfeeding. It has been suggested that an increase in peripheral blood flow induced by oestrogens could stimulate faster nail growth. A general strengthening of growth processes could also explain this phenomenon.

  Puberty is also another life stage subject to hormonal fluctuations. It is said that nail growth reaches its peak during puberty and decreases as hormone levels balance with age, to about 50% of its previous rate.

• Onychophagy: The chronic habit of biting one's nails has been associated with a faster growth rate. This can be explained by the fact that biting the nail causes micro-trauma, which stimulates blood circulation in the nail bed located underneath to ensure the protection of the digital extremities again. This also indirectly confirms the theory that frequently cutting the nails makes them grow a little faster.

• Gender: Men's nails appear to grow relatively quickly compared to women's. In a study focusing on young Japanese individuals, researchers found that the average growth rates of the thumbnail were 3.06 millimetres per month for men and 2.94 millimetres per month for women.

• Medical treatments: On the other hand, certain medications or anti-cancer treatments such as chemotherapy can lead to a global reduction in the rate of nail growth, or even cause them to fall out, due to their anti-mitotic effects (blocking the process of cell division).

If you feel that your nails are growing at an unusually slow rate, discuss this with your doctor. Your symptoms could be related to nutritional deficiencies or another underlying condition.

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