Trimming fingernails and toenails to make them more aesthetically pleasing could be detrimental and potentially lead to serious nail conditions.
Researchers at the University of Nottingham in the United Kingdom found that nail grooming may cause some of the most common nail problems, such as ingrown toenails, spoon-shaped nails and pincer nails. Regular poor trimming can tip the fine balance of nails, causing residual stress to occur across the entire nail.
"It is remarkable what some people are willing to do to make their nails look good, and it is in this context that I decided to look at what we really know about nails," said Cyril Rauch, lead author of the study. "Reading the scientific literature on nails I quickly realized that very little physics or math had been applied to nails and their conditions."
For the study, researchers focused specifically on ingrown toenails which, though recognized for a long time, still lack a satisfactory treatment as the causes remain largely unknown. When devising their equations, the researchers accounted for the strong adhesion of nails to their bed through tiny, microscopic structures, which allow the nail to slide forwards and grow in a "ratchet-like" fashion by continuously binding and unbinding to the nail. By also taking into account the mechanical stresses and energies associated with the nail, the researchers came up with an overall nail shape equation.
The equation showed that when the balance between the growth stress and adhesive stress is broken -- if a nail grows too quickly or slowly, or the number of adhesive structures changes -- a residual stress across the entire nail can occur, causing it to change shape over time.
Residual stress can occur in any fingernail or toenail; however, the stress is greater for nails that are larger in size and have a flatter edge, which explains why ingrown toe nails predominantly occur in the big toe.
The equation also showed that bad trimming of the nails can amplify residual stress.
"Looking at our results, we suggest that nail beauty fanatics who trim their nails on a daily basis opt for straight or parabolic edges, as otherwise they may amplify the imbalance of stresses which could lead to a number of serious conditions," Rauch said.
Moving forward, Rauch believes this research can be applied to farm animals and conditions associated with their hooves, which can be life threatening.
"Animals such as sheep, cattle, horses and ponies all suffer hugely from hoof conditions, which can have direct effects on the human population. At a time when securing food across the world is important, understanding the physics of hooves has never been so essential to sustain agriculture and food production," Rauch continued.
The findings were published in the journal Physical Biology.
