Nails are made of a protein called keratin – these cells get pushed outward from the nail bed, forming the nail plate, also known as the toenail. The toenail adheres to the nail bed because of a collection of ridges that connect the two together. If the keratin cells multiply too often over a period of time, then the nail grows very quickly as well. Combined with the adhesion process, the nail’s curvature changes faster than normal and leads to the nail piercing the sides of the nail bed.
Given that ingrown toenails can be caused by swift nail growth, it’s no wonder that pregnant women and children are more prone to ingrown nails. Both of these populations are producing a lot of growth hormones – the pregnant women to nourish the pregnancy, and children to help them become healthy adults.
Ingrown nails can also be caused by the reverse issue: the toenails growing too slowly. In elderly populations, growth hormones are not present in the same way. Still, the adhesion strength of the ridges stays the same, and the nail curls inward while still adhering to the nail bed. This causes a more curved ingrown toenail, which can be just as painful.
This overgrowth or undergrowth is not based in biology – it’s based in physics. The wrong combination of physical cell growth, stress and force applied to the nail, and strength of nail adhesion can lead to soreness, pain, and swelling. To prevent ingrown toenails, regular trimming is recommended because it reduces the amount of stress and force applied to the nail plate. You can’t change the rate of growth or the way the nail adheres, but you can keep an eye on the nails as they develop and make sure you aren’t headed toward developing this painful condition.
Fun Fact: Other animals get something similar to “ingrown toenails” as well! Keratin is also found on hooved animals and can cause similar issues if the growth rate is too fast or slow.