Ingrown toenails develop when the edge of the nail grows into the soft skin alongside it, triggering pain, swelling, and sometimes infection. The big toe is the most common site, and the cause is rarely just one thing. A combination of how you trim your nails, what shoes you wear, your inherited nail shape, and even how much your feet sweat can all push the nail into the surrounding skin.
How the Nail Grows Into the Skin
The most widely accepted explanation is straightforward: the edge of the nail plate digs into the overlapping fold of skin beside it, creating a small wound. Your body responds with inflammation and, if the pressure continues, builds up a mound of raw, reddish tissue called granulation tissue. That tissue swells further into the nail’s path, making the problem worse.
There’s also an alternate view that focuses less on the nail itself and more on the skin around it. In some people, the soft tissue alongside the nail is naturally wider or puffier, and it bulges up against the nail edge. Over time, constant pressure between skin and nail causes tissue breakdown. In practice, both mechanisms often work together: a slightly curved nail meets slightly excess skin, and external forces like tight shoes or ground impact seal the deal.
Trimming Mistakes That Start the Problem
The single most controllable cause is how you cut your toenails. Two common habits create trouble: cutting nails too short and rounding the corners. When you trim a nail short and curved, the skin at the sides can fold over the nail edge as it regrows. The new nail then has to push through that skin rather than glide over it. Cutting nails into a pointed V-shape causes the same issue from a different angle, leaving sharp edges that act like tiny spikes.
The fix is simple: cut straight across and leave enough length so the corners of the nail sit loosely against the skin on either side. If the corners are already embedded, trying to dig them out with clippers or a sharp tool typically makes the inflammation worse and can introduce bacteria.
Shoes That Squeeze the Toes
Tight or narrow footwear is one of the most common contributing factors, especially shoes with a tapered toe box. Inside that confined space, the big toe gets pushed toward the second toe, and the pressure falls directly on the outer edge of the nail. Research published in the Journal of the American Podiatric Medical Association found that when the first and second toes are pressed together (simulating a tight shoe), the bony structures of the second toe push against the area of the big toe where ingrown nails typically form. That sustained pressure prevents the nail from growing outward normally.
Athletic footwear can cause the same problem for a different reason. Cleats, running shoes, and court shoes that are even slightly too small subject the toes to repetitive impact with every stride, jump, or lateral cut. Sports involving running, jumping, or quick direction changes place extra force on the toes, and over time those repeated micro-impacts can drive the nail edge into the skin.
Nail Shape You Inherited
Some people get ingrown toenails no matter how carefully they trim or what shoes they wear, and genetics are often the reason. Nail shape is largely inherited. People with pincer nails, where the nail naturally curves inward on both sides rather than lying flat, are at significantly higher risk because the edges of their nails are essentially always pressing into the skin. Fan-shaped nails that widen toward the tip and unusually thick nail plates can also predispose you to the problem.
If your parents or siblings deal with recurring ingrown toenails, you likely share the same nail geometry. This doesn’t mean the condition is inevitable, but it does mean you’ll need to be more deliberate about trimming technique and shoe selection than someone with naturally flat nails.
Sweating and Fungal Infections
Excessive foot sweating, particularly common in adolescents, softens the skin around the nail through a process called maceration. When that skin stays damp for hours, it loses its structural integrity. A softened, waterlogged nail fold is much easier for the nail edge to pierce. At the same time, moisture makes the nail plate itself more flexible, which sounds like it would help but actually allows the nail to bend and curve into the skin more easily.
Fungal nail infections contribute through a different path. A fungus-damaged nail becomes thicker, more brittle, and irregularly shaped. Those distortions change how the nail sits in its groove and create uneven edges that are more likely to catch on the surrounding skin. Having both excessive sweating and a fungal infection at the same time, which is not uncommon since moisture promotes fungal growth, compounds the risk considerably.
Diabetes and Circulation Problems
Diabetes doesn’t directly cause ingrown toenails, but it creates conditions that make them more likely and far more dangerous. People with diabetes often develop nerve damage in their feet (peripheral neuropathy), which means they can’t feel the early pain of a nail pressing into skin. Without that warning signal, the ingrown nail progresses further before it’s noticed, and by that point infection may already be underway.
Poor circulation, another common complication of diabetes, affects the nail in multiple ways. Reduced blood flow to the toes impairs the nutrition reaching the nail unit, leading to thicker, more brittle nails with disrupted structure. Those nails are harder to trim cleanly and more prone to developing irregular edges. Vascular disease also increases susceptibility to bacterial and fungal infections of the feet, which can accelerate an ingrown nail from a minor annoyance to a serious wound.
There’s also a gait component. Diabetes-related neuropathy often shifts how pressure is distributed across the foot, increasing stress on the forefoot and toes. That extra mechanical force pushes the nail against the soft tissue of the nail groove with every step, a subtle but constant driver of ingrown nail development that the person may not even feel happening.
Other Contributing Factors
Trauma to the toe, whether from stubbing it, dropping something on it, or sustaining a sports injury, can alter how the nail grows back. A single significant injury or repeated minor ones can damage the nail matrix (the tissue that produces the nail), leading to a nail that grows thicker, curved, or at an unusual angle.
Obesity increases the downward force on the toes with every step, amplifying the same mechanical pressure that tight shoes create. Pregnancy can contribute similarly through weight gain combined with swelling in the feet and the difficulty of reaching your toes to trim nails properly in the third trimester.
Age plays a role at both ends of the spectrum. Adolescents are prone to ingrown toenails partly because of increased foot sweating and partly because feet grow quickly, making it easy to end up in shoes that are too small. Older adults face risk from thickened nails, reduced flexibility that makes proper trimming difficult, and higher rates of diabetes and circulation problems.
How to Reduce Your Risk
Since ingrown toenails usually result from multiple factors stacking up, prevention means addressing as many of those factors as you can. Cut your nails straight across, keeping them long enough that the corners aren’t buried in skin. Choose shoes with a toe box wide enough that your toes aren’t pressed together, and make sure athletic shoes fit properly with about a thumb’s width of space between your longest toe and the end of the shoe.
If your feet sweat heavily, changing socks during the day and choosing moisture-wicking materials can help keep the skin around your nails intact. For people with naturally curved nails or a family history of ingrown toenails, periodic visits to a podiatrist for professional trimming can prevent the cycle of home trimming mistakes that often triggers flare-ups. And if you have diabetes, regular foot checks are essential, since you may not feel the early signs that something is wrong.