Ingrown toenails most often result from improper nail trimming, which leaves a small spike of nail that digs into the surrounding skin as it grows. Tight shoes, inherited toe anatomy, and repetitive pressure from sports or excess body weight also play significant roles. In most cases, more than one of these factors is at work simultaneously.
How Trimming Creates the Problem
Cutting your toenails too short or rounding off the edges is the single most common trigger. When you curve the nail along the corners instead of cutting straight across, the remaining edge can form a sharp spike. As the nail grows forward, that spike pushes directly into the soft skin fold beside it, puncturing it like a splinter. The body treats the nail fragment as a foreign object, launching an inflammatory response that produces the redness, swelling, and pain you feel.
Cutting nails too short causes a related problem. The pressure from your shoes pushes the skin up and over the shortened nail edge, and as the nail regrows it has nowhere to go but into the tissue. The correct approach is to cut straight across and leave the nail long enough that its corners rest loosely against the skin on either side, without rounding the edges or trimming into a V-shape.
Shoes and Repetitive Pressure
Footwear that crowds your toes pushes the skin against the nail edge for hours at a time. Narrow dress shoes, pointed-toe heels, and cleats that are even slightly too small all create this compression. Over time, the constant pressure guides the nail’s growth path into the surrounding tissue rather than straight outward.
Athletic activity adds another layer of force. Every step generates reactive ground forces that push up through the toe, and running, soccer, basketball, and other stop-and-start sports amplify that impact. The repeated micro-trauma from your toe hitting the front of your shoe can bruise the nail bed and nudge the nail edge deeper into the skin fold. Obesity increases these forces further, since every stride carries more downward pressure through the feet.
Anatomy You Inherit
Some people are structurally more prone to ingrown nails regardless of how they trim or what shoes they wear. A study comparing patients with unilateral ingrown toenails to matched healthy controls found three anatomical traits that significantly predicted the condition: wider nail folds (the skin ridges flanking the nail), thicker nail plates, and greater inward rotation of the big toe. A mathematical model based on just these three measurements correctly identified 85% of patients and 80% of controls, suggesting that for most people who get ingrown toenails, a built-in anatomical predisposition exists and external factors like trimming or footwear simply act as triggers.
If your parents or siblings deal with recurring ingrown nails, your toe shape likely puts you in the same risk category. Pincer-shaped nails, which curve sharply inward on both sides, are a particularly common inherited pattern that makes ingrowth almost inevitable without careful maintenance.
Sweating, Fungal Infections, and Soft Skin
Excessive foot sweating weakens the skin around the nail by keeping it constantly damp, a process called maceration. Waterlogged skin loses its structural integrity, making it far easier for even a slightly curved nail edge to pierce through. This is especially relevant in teenagers, who tend to sweat more from their feet and who already represent the highest-risk age group (the peak incidence falls between ages 11 and 30).
Fungal nail infections contribute differently. Rather than softening the skin, they thicken and distort the nail plate itself, changing its shape and growth direction. A nail that has become warped or abnormally thick from a fungal infection is more likely to press into the surrounding tissue. Managing either condition, whether through moisture-wicking socks and breathable shoes for sweating or antifungal treatment for infected nails, reduces the likelihood of ingrowth.
Medications and Other Triggers
Certain cancer drugs that target a specific growth receptor on skin cells are known to cause ingrown toenails as a side effect. These medications alter the way nail and skin tissue grow, making ingrowth a common complication during treatment. If you’re undergoing cancer therapy and notice nail changes, your oncology team can help manage the issue early.
Direct trauma to the toe, such as stubbing it hard, dropping something on it, or losing a toenail from injury, can also set the stage. Damage to the nail matrix (the tissue under the cuticle that produces the nail) may cause the nail to grow back irregularly, with edges that angle into the skin. A prior nail surgery carries similar risks if the nail root wasn’t fully addressed.
What Happens When It Gets Infected
An ingrown nail that merely presses into the skin causes pain and redness but isn’t necessarily infected. Infection develops when bacteria enter through the break in the skin, producing warmth, increasing swelling, and sometimes causing pus to collect around the nail fold. Soaking the toe in warm water for about 15 minutes a few times a day can help drain mild buildup and relieve pressure.
If soaking doesn’t improve symptoms within a day or two, or if the redness is spreading, the pain is worsening, or you notice significant pus, professional treatment is needed. This is especially urgent for anyone with diabetes, poor circulation, or a weakened immune system, since infections in these groups can escalate quickly. A provider may drain the area, prescribe antibiotics, or in recurring cases, perform a minor procedure to prevent the nail edge from growing back into the skin.
Preventing Recurrence
Since ingrown toenails often come back, prevention matters as much as treatment. The most impactful habit is trimming correctly: cut straight across with clean, sharp clippers and resist the urge to round the corners or peel off edges. Leave the nail just long enough that you can see a thin white margin at the tip and the corners sit on top of the skin, not buried beneath it.
Footwear choices are the second line of defense. Your shoes should allow your toes to move freely without pressing against the sides or front. If you play sports, make sure athletic shoes fit with about a thumb’s width of space between your longest toe and the end of the shoe. Keeping your feet dry with moisture-wicking socks and breathable materials helps maintain skin integrity around the nail. For people with an inherited nail shape that makes recurrence nearly guaranteed, a minor procedure to permanently narrow the nail can break the cycle.