An ingrown toenail, or medically termed onychocryptosis, is something no one is really fond of; still, when one appears, your instinct may be to cut the offending bit. However, new research suggests that may not be exactly the right thing to do as it won’t necessarily prevent the toenail from growing in again. The root cause actually lies in physics.
Physicists Cyril Rauch and Mohammed Cherkaoui-Rbati, of the University of Nottingham in England, carried out a study where they closely examined the mechanical forces acting on fingernails and toenails, including the outward growth of the nail and the tension of its attachment to the nail bed.
Made of the protein keratin (just like hair), nails are attached to the nail bed with structures that are microscopic yet quite strong. Breaking this attachment is quite painful.
The study revealed that ingrown toenails are caused by an imbalance in the forces acting on them. Typically, nail growth exerts a force on the nail — pushing it outward toward the tip of the finger which works against the adhesive force holding the nail down to the nail bed.
But, when the nail grows too fast, the balance between these forces is disrupted. The additional force from the growth strains the nail bed which results in the nail edge becoming more curved.
Besides, the shape of the nail plays a role in making it ingrown. Because fingernails are naturally curved, the outer edges are shorter than the center. This means the rates of growth in the different parts of the nail are slightly different — the center grows a bit slower than the edges do.
According to Rauch the distal part, the separation between the white and pink part, has a curved shape which is creating the stresses.
Eventually, this stress causes the far edge of the nail to poke down into the skin alongside the nail, leading to an ingrown nail, the researchers found.
These forces are also the reason that the big toe seems especially prone to ingrown nails, Rauch said. “This curvature [on the edge of the big toenail] is very flat. By being flattened, these [nails] will generate stress in the transverse direction,” he said. In other words, because the edge of this toenail tends to be straighter, the rate of growth in a big toe needed to push the edge of the nail into the skin doesn’t need to change as much as it does for other nails.
To clip or not to clip?
Cutting the ingrowing edge of the nail is not always helpful because it doesn’t always rebalance the forces acting on the nail. When you cut off the end of the nail, depending on the shape of the cut, you change the nail’s shape. But the faster- and slower-growing parts of the nail will keep growing at the same rates, so the change in the shape might get the nail to grow correctly — or it might not.
The best option seems to be to cut the nail in a parabolic shape, such as an oval, or to cut the edge so that it is slightly curved, rather than straight across at the end of the nail, the researchers said. That method seems to cause the force on one part of the nail and bed to balance the forces from the other parts, they added.
Rauch noted that pregnant women and children tend to get ingrown toenails more often than other groups of people. That may be because there’s generally more growth happening in the nails for both of those groups, he said.