Ingrown toenails develop when the edge or corner of a nail grows into the soft skin alongside it, acting as a foreign body that triggers pain, swelling, and sometimes infection. The big toe is the most common site. Understanding the specific causes helps you prevent them from happening in the first place.
How the Nail Pierces the Skin
A thin layer of skin lines the groove where your nail meets the surrounding tissue. Under normal conditions, this layer protects the groove from irritation. But when something disrupts the fit between the nail and its groove, sharp edges or spicules form along the nail’s lateral margin. These tiny spikes gradually dig into the deeper layers of skin as the nail grows forward.
Once the nail breaks through, your body treats it like a splinter. The immune system launches an inflammatory response: redness, swelling, tenderness, and sometimes pus. If the irritation continues, granulation tissue (a bumpy, raw-looking overgrowth of healing tissue) can form around the area, making the problem worse and harder to resolve on its own.
Cutting Your Nails Wrong
Improper trimming is the single most common preventable cause. Three specific mistakes create the conditions for an ingrown nail:
- Cutting too short. When you trim a nail below the tip of the toe, the skin at the sides can fold over the nail edge as it regrows, guiding it into the flesh.
- Rounding the corners. Digging your clippers into the corners to create a curved shape leaves behind small nail fragments that act as spicules, piercing the surrounding skin as the nail grows out.
- Not cutting straight across. Angled or jagged cuts produce uneven edges that are more likely to catch on the nail groove and redirect growth into the skin.
The American Academy of Dermatology recommends cutting toenails straight across with a dedicated toenail clipper (not the smaller fingernail type). Toenails grow more slowly than fingernails, so they don’t need trimming as often. Keeping them roughly even with the tip of the toe hits the sweet spot: not so short that skin folds over them, not so long that shoes push them back.
Tight Shoes and High Heels
Footwear that squeezes your toes is the other major culprit. The front of the shoe, called the toe box, determines how much room your toes have. When that space is narrow or pointed, toes press against each other and against the sides of the shoe. This constant pressure pushes the nail sideways into the skin, especially on the big toe.
High heels compound the problem. Elevating the heel shifts your body weight forward, thrusting your toes into the front of the shoe. You end up with intensified pressure in an already tight space. The material matters too: stiff, non-breathable shoes hold your foot rigidly, while softer materials with some flex allow your toes to spread naturally during movement.
Sports and Repetitive Impact
Athletes, particularly runners and soccer players, deal with ingrown toenails at higher rates. Two mechanisms are at work. First, repetitive pounding on hard surfaces causes microtrauma to the nail and the tissue around it. In continuous running, the nail gets hammered with every stride, which can cause it to thicken and harden over time. Research published in the Journal of the American Podiatric Medical Association found that runners with harder, less flexible nails had the highest rates of ingrown toenails. A rigid nail is less able to absorb impact and more likely to dig into the surrounding skin.
Second, exercise produces excessive sweating, which softens the skin folds around the nail. When the skin is soft and waterlogged, even a minor nail spicule can puncture it easily. The combination of a hardened nail and softened surrounding skin creates the perfect setup for an ingrown nail to develop during or after intense physical activity.
Nail Shape and Genetics
Some people are simply more prone to ingrown toenails because of the shape they inherited. Nails that are naturally curved (sometimes called pincer nails), unusually thick, or fan-shaped put more pressure on the nail groove even without any external factors. If your parents dealt with chronic ingrown toenails, there’s a good chance you will too.
Nail shape also interacts with other risk factors. A highly curved nail in a tight shoe, for instance, is far more likely to become ingrown than a flat nail in the same shoe. People with naturally problematic nail shapes often benefit from more frequent, careful trimming to keep edges from catching on the surrounding skin.
Diabetes and Poor Circulation
People with diabetes face a higher risk of ingrown toenails, and the consequences can be more serious. A study examining diabetic patients with ingrown nails found that nearly 47% of them also had peripheral arterial disease, meaning reduced blood flow to the feet. Poor circulation slows healing, making even a minor nail-related wound more likely to become infected or develop into an ulcer.
The same study identified a weak pulse in the foot’s main artery as a significant predictor of ingrown nails, nearly tripling the odds. Diabetic nerve damage also plays a role: if you can’t feel the early pain of an ingrown nail, you’re less likely to catch it before it progresses to infection.
Other Contributing Factors
Toe injuries can trigger ingrown nails. Stubbing your toe, dropping something on it, or any trauma that damages the nail matrix (the tissue beneath the cuticle where the nail grows from) can alter how the nail grows out, sending it into the skin at an abnormal angle. Even a single event can cause problems weeks later as the damaged section of nail slowly grows forward.
Fungal nail infections thicken and distort the nail plate, making it wider and more irregular. The misshapen nail presses harder against the groove and is more difficult to trim cleanly. Obesity adds pressure to the feet with every step, and excessive moisture from sweating or poor foot hygiene softens the nail folds, lowering the threshold for penetration.
What Progression Looks Like
Ingrown toenails typically worsen in stages if left untreated. Early on, you’ll notice tenderness and slight swelling along one side of the nail. The skin may look pink or red and feel firm to the touch. At this point, warm soaks and proper trimming can often resolve the problem.
If the nail continues to press into the skin, the inflammation intensifies. The area becomes more swollen, noticeably painful during walking, and may start to drain clear or yellowish fluid. In the most advanced stage, the body builds granulation tissue over and around the embedded nail edge, and bacterial infection can set in, producing pus and a spreading area of redness. At this stage, the nail typically needs professional treatment to remove the embedded portion and address the infection.
Practical Prevention
Most ingrown toenails are avoidable with a few consistent habits. Trim straight across with a proper toenail clipper, leaving the nail even with the tip of the toe. Disinfect your clippers monthly by scrubbing them with isopropyl alcohol (70 to 90 percent), rinsing in hot water, and drying completely before storing.
Choose shoes with a roomy toe box that lets your toes lie flat without pressing against each other or the sides. If you run or play sports that involve sudden stops and direction changes, make sure your athletic shoes fit with about a thumb’s width of space between your longest toe and the front of the shoe. Moisture-wicking socks help keep the skin around your nails from getting waterlogged during exercise. If you have naturally curved nails, diabetes, or circulation problems, regular check-ins with a podiatrist can catch early changes before they become painful.