Ingrown toenails happen when the edge or corner of a nail grows into the soft skin beside it, triggering pain, swelling, and sometimes infection. The big toe is the most common site. While the immediate cause is mechanical (a sharp nail edge pressing into flesh), the reasons that edge ends up there in the first place range from how you trim your nails to the shoes you wear to the shape you inherited.
How the Nail Actually Digs In
Your toenail grows forward from a root tucked under the skin at the base of your toe. Normally, the nail slides along a shallow groove on each side without trouble. Problems start when something changes the relationship between the nail plate and the skin fold running alongside it. Either the nail curves more than it should, or the skin gets pushed into the nail’s path, or a jagged edge from a bad trim acts like a tiny blade. Once the nail edge breaks the skin surface, your body treats it like a foreign object. Inflammation kicks in, the tissue swells, and that swelling presses even harder against the nail, creating a cycle that gets worse on its own.
Trimming Mistakes Are the Top Cause
The way you cut your toenails has a direct effect on how they grow. Two trimming habits cause the most trouble: rounding the corners and cutting too short. When you round the edges, you remove the nail’s natural corner, which normally sits on top of the skin fold. As the nail regrows, it has no guide keeping it on the surface, so it curves downward into the flesh. Cutting too short creates a similar problem by letting the surrounding skin fold over the nail’s edge, trapping it as it grows forward.
Digging into the sides of the nail with clippers or a pointed tool is another common trigger. It damages the skin along the nail groove, creating inflammation that makes the tissue swell into the nail’s path. The fix is straightforward: trim straight across so the corners sit just above the skin, keep the nail roughly even with the tip of your toe, and use toenail clippers (not fingernail clippers, which can split thicker toenails and leave ragged edges). A nail file can smooth any sharp corners without removing them entirely.
Shoes That Squeeze Your Toes
A narrow or pointed toe box cramps your toes together and presses them against the shoe’s sides. That constant pressure pushes the skin fold into the nail edge, especially on the big toe. Over hours of wear, this is enough to start the nail digging in. High heels make things worse in a specific way: elevating the heel shifts your body weight forward, thrusting your toes into the front of the shoe. The combination of a constricted space and intensified downward pressure significantly raises the risk.
Shoes that are simply too small have the same effect. If your toenails are hitting the end of your shoe when you walk, that repeated contact pushes the nail back into the nail bed and can redirect growth into the surrounding skin.
Sports, Trauma, and Repetitive Impact
Runners, soccer players, and anyone whose sport involves repeated toe impact face a higher rate of ingrown nails. Each stride in a long run sends your toes forward into the shoe. Kicking a ball loads force directly onto the toenail. Over weeks of training, this repetitive microtrauma can alter how the nail sits in its groove or cause small cracks at the nail edge that become ingrown as they grow out. A single acute injury, like stubbing your toe hard or dropping something on it, can do the same thing in one moment by cracking or lifting the nail plate.
Genetics and Nail Shape
Some people are simply built for ingrown nails. Inherited traits play a real role. A nail plate with increased curvature (sometimes called a pincer nail) naturally presses into the skin on both sides as it grows. Wide, fleshy nail folds that crowd the nail also raise the odds. Some infants are born with a misaligned great toenail or oversized lateral nail folds, a congenital form that can cause problems from very early in life. If ingrown toenails run in your family or keep coming back despite good trimming habits, your nail anatomy is likely a contributing factor.
How Ingrown Nails Progress
Ingrown toenails don’t stay the same if left alone. They move through recognizable stages, and knowing which one you’re in helps you gauge how urgently to act.
In the earliest stage, the end of the toe becomes red with mild swelling. It feels warm and is painful to touch, but there’s no pus or drainage. Many ingrown nails at this point resolve with warm soaks, proper trimming, and roomier shoes.
In the second stage, redness, swelling, and pain increase noticeably. You may see white or yellow pus draining from the side of the nail, a sign that infection has likely developed. This stage typically needs more active intervention.
The third stage involves significant swelling, continued pus discharge, and the growth of new, bumpy tissue (granulation tissue) along the nail fold. The skin around the nail may start to overgrow, making the problem self-sustaining. In more severe cases, the infection can spread and cause fever.
Why Diabetes Makes It More Dangerous
For most people, an ingrown toenail is painful but manageable. For people with diabetes, it can become a serious medical event. Diabetes causes two problems in the feet that compound each other: reduced blood flow and nerve damage. Poor circulation slows healing. Nerve damage (peripheral neuropathy) dulls sensation, so you may not notice the pain, swelling, or warmth of an ingrown nail until it has already progressed.
An ingrown toenail in a person with diabetes can develop into a diabetic ulcer, an open wound that is slow or difficult to heal. Without treatment, these ulcers can lead to deep infection and, in severe cases, gangrene and amputation. This is why routine foot checks and professional nail care matter so much for anyone living with diabetes.
Preventing Recurrence
If you’ve had one ingrown toenail, you’re more likely to get another, especially if the underlying cause (nail shape, shoe choice, trimming habit) hasn’t changed. A few practical adjustments cut the risk substantially:
- Cut straight across. Use sharp, clean toenail clippers designed for toenails. Trim straight, then lightly file any sharp edges. Don’t round the corners or peel the nail.
- Leave enough length. The nail’s corners should sit loosely against the skin at the sides of your toe. If you can see pink skin at the corners, you’ve cut too short.
- Choose shoes with a roomy toe box. Your toes should be able to wiggle freely. Avoid pointed styles and limit time in high heels.
- Protect your toes during sports. Properly fitted athletic shoes and moisture-wicking socks reduce friction and impact. Keep nails trimmed before long runs or games.
- Don’t dig into the sides. Resist the urge to clean under the nail edges with sharp tools. This traumatizes the skin fold and invites the nail to grow in.
For people whose nail shape or curvature makes ingrown nails a recurring problem despite good habits, a podiatrist can perform a procedure that removes a narrow strip of the nail along with the part of the root that produces it. This prevents that section of nail from regrowing and is one of the most effective long-term solutions for chronic cases.