Twenty-five years of practice in dermatology has taught me that ingrown toenails have little or nothing to do with whether nails are cut straight across or with a curve. What you mostly read is 'cut toenails straight or you'll get ingrown nails'. The message comes from supposed experts such as podiatrists and doctors. Every child on the face of the earth grows up thinking this. And why not? They hear it from grown-ups who must know everything. Grown-ups, after all, are supposed to know stuff.
Once again, I am here to dispel another myth: the myth of the straight-cut toenail. There is no evidence to support the notion that cutting nails with a curve causes ingrown nails, or that cutting straight prevents them. Those who preach straight-cut are merely perpetuating unsubtantiated traditional beliefs. Studies have not been done and closer examination of the rationale exposes its faults.
In every case I've seen, and there have been many, patients have always done exactly as they were told: they cut their toenails straight across and still developed ingrown toenails. Ingrown nails are more about an individual's own anatomy, plus, in some cases, trauma from shoes.
The photograph below shows a typical ingrown toenail. The nail is straight-cut, but the ingrown nail goes nearly to the cuticle. The manner in which the nail was cut couldn’t have influenced the ingrown nail close to the cuticle.
What, then, is an ingrown nail? Most importantly, it appears NOT to be an infection in the true sense, i.e. caused by bacteria. Most cases of ingrown nail don't respond at all to antibiotics. Instead, an ingrown nail results when the tissues at the side of the nail get irritated, inflamed, and swollen, leading to redness, pain, and tissue breakdown with oozing and pus. There is one exception: if you cut too close and injure the skin, you can introduce real infection, but it behaves differently: more rapid in onset, more painful, and responds to antibiotics.
It is thought that the sides of the nail must play a role in ingrown nails, that the edge 'digs' into surrounding tissue, either naturally or from shoe pressure. We know this because the problem goes away when the lateral sides of the nail or excess nail fold skin are permanently removed by surgery. Whether from the nail itself, or excessive surrounding skin, the individual's reaction to microscopic trauma is probably a key factor.
What makes NO sense is the belief that cutting the nail influences how a nail grows. If that were the case, we might expect to see it happen with finger nails, but we don’t: fingernails and toenails grow out regardless of how they are cut. Nails grow by sliding horizontally outward from the cuticle area. Whether you cut straight or curved, the nail still slides toward the tip in the way it is genetically programmed to do. The white part that gets clipped away has already separated from its base (the nail bed), and even if you cut too close, it cannot influence how the nail grows.
The big question is whether we have ANY control over preventing ingrown toenails. My suspicion is that we do not. Reasonable hygiene (but not too aggressive) is as much as we can recommend. Plenty of toe space in shoes also seems wise (but not proven). All definitive treatments, however, involve surgery, although many devices and practices to flatten out the nail have been tried with mixed results.
It would be good if someone did a scientific study of curved cut versus straight cut, but since this is a non life-threatening condition, it’s not likely to happen. In the meantime, if you would like some contour with your pedicure, give it a try. If you have never had ingrown nails, the odds are in your favor. Go easy at first. A little rounding of the edges of the big toenail won't hurt you.
