The short answer is that there is no 100% definitive known reason as to why nails grow at different rates. However, there is a really good theory (which also covers why fingernails and toenails grow at drastically different rates) that is backed up by an awful lot of ancillary evidence. To fully grasp what’s going on here, it’s important to understand exactly how your fingernails grow.

Every type of cell in our body grows at different rates. For example, we know that hair grows faster than bones and cancer grows faster than anyone would like. The exact mediating factor of what gives rise to that growth rate is still the topic of much research. What we do know is that the answer lies in our genes.

Now it should be noted that in August of 2012, a team of researchers at MIT and the Harvard Medical School were able to answer when mammalian cells decide to divide. They found that cells divide when they reach a critical phase in development, not when they reach a specific size. This breakthrough in understanding will now allow them to test the factors that determine why they might grow and divide at those rates.

But as to finger and toenails, what we know about fingernails is that they grow at a rate of about 3.5 millimeters per month and toenails grow about 1.6 mm per month on average. The exact rate at which your nails will grow depends on several factors. They include things like: age, sex, diet, exercise, and even the time of year.

Our nails consist of many different parts. The visible part is known as the nail plate. Below this is the nail bed. The white, half-moon shaped part at the base of your nail is called the lunula (also known as the distal matrix). The tissue over the top of the matrix is called the cuticle, and the soft tissue directly over your cuticle, is called the eponychium.

The nail itself is grown from the matrix (presumably your big toe is “The One”). It lies beneath the fingernail and extends several millimeters into the finger. 90% of nail growth comes from here. The matrix consists of epithelial cells (the most common type of cells that make up numerous things in our bodies, like skin) that grow and divide. These cells contain proteins called keratin. Once the cells begin to reach the end of their life cycle, they go through a process called Keratinization, also known as cornification.

When the cell dies, it loses its nucleus and other intracellular organelles. What remains is keratin.  It gets enclosed in an insoluble mixture of different proteins and lipids (fats). The enzyme responsible for this formation is known as Transglutaminase. The result is the hard nail used to pick noses and give back scratches everywhere!

Pressure within the matrix of your nail forces the dead karatinized cells out. The shape of your nail, as it grows, is merely a continuation of the angle of your matrix. It’s then guided along by the nail grooves and folds on the sides of your nail bed.  Keratinized cells are not just found in your nails, but also in your hair, skin, and animal hooves. What makes them more hard, or soft, depends on their thickness and the cross-linked structure of the keratin.

Now that we know how our nails grow, let’s get back to the specific question at hand and talk about the main theories behind why fingernails grow faster than toenails and why nails on different fingers or toes grow at different rates.  In the end, it really just seems to come down to blood supply, but there’s a bit more to it than just that certain fingers or toes are getting a better and more oxygen rich blood supply than others.

The matrix in our nails is supplied with blood and nutrients through a highly vascular area of capillaries. They also have special shunts (blood pathways) between the arteries and veins known as Sucquet-Hoyer canals, that help regulate temperature in your fingers and toes when it gets cold.

When any part of our body gets injured, the natural reaction is a response that engorges the area with more blood and nutrients. So it is believed that the constant micro trauma our fingernails endure throughout the day, like tapping, typing, and bumping, allows for an even greater increase in blood and nutrient supply. Since the toes are always kept locked away safely in our socks and shoes (and in an office like environment, we’re often immobile throughout much of the day, but constantly using our fingers as we type), they don’t receive the constant “mini-trauma” that the fingernails do.  Similarly, certain fingers and toes likely get more trauma than others, affecting their growth rate. The end result of these micro traumas is a chronic overabundance of nutrients that make more karatinized epithelial cells. The increase results in more nail.

The reason the “trauma” theory is adopted by many researchers revolves around ancillary evidence. Fingernails on your dominant hand will grow faster than the ones on your non-dominant hand, presumably because your dominant hand will have more micro trauma compared to your non-dominant hand.

Additional ancillary evidence towards the overarching “blood supply” theory is that nails will grow faster in the summertime. Since your fingers and toes are warmer, your capillaries and arterioles are bigger, allowing more blood-flow to the digits. When circulation becomes an issue, like as we age or in certain medical conditions like diabetes, the nails will grow slower.

So there you have it Aaron.  Not absolute proof as to why your fingernails grow faster than toenails, but the thought process sure makes sense, even if it’s not as exacting as I normally like to be in these articles!  Time and researchers putting forth the effort I’m sure will have a more definitive answer for us soon, perhaps getting a little more specific!  But for now this will have to do for an answer.

If you liked this article and the Bonus Facts below, you might also like:

• 10 Fascinating Facts About the Human Body
• Why Papercuts Hurt So Much
• There is No Difference Between Fur and Hair
• Why Fingers Wrinkle in Water

Bonus Facts:

• The distal matrix (the lunula) appears white, beneath our fingernails because there are no melanocytes present in this portion of the nail. Melanocytes are the cells that give our skin, hair, and eyes their color.
• The average thickness of a fingernail is .5-.7mm. They form and are present after the 10^th week of pregnancy.
• In the article, I mentioned the exact mediating factor of growth rates appears to be genetic. There are currently 54 known functional keratin genes. They are separated into 2 types. There are 28 type 1, and 26 type 2 keratins. They are located in clusters on chromosome 12 and 17.
• The longest fingernails ever recorded, belonged to Melvin Boothe of the United States. They had a combined length of 32 feet 3.8 inches. Sadly he died in December of 2009. The longest fingernails ever recorded on a women, belonged to Lee Redmond of Las Vegas. They measured 28 feet 4.5 inches. While Lee is still alive, she lost her fingernails in a car accident in 2009. It would appear 2009 was a bad year for those with extremely long fingernails!