Ingrown toenails develop when the edge of a nail, usually on the big toe, curves or gets pushed into the soft skin alongside it. A sharp sliver of nail gradually digs into the skin fold, and your body treats it like a foreign object, triggering pain, swelling, and sometimes infection. The process can happen slowly over weeks or quickly after a single injury, and a few common habits are responsible for the vast majority of cases.
What Actually Happens Inside Your Toe
Your toenail sits in a groove of skin on each side. When the nail’s edge doesn’t fit properly in that groove, small sharp spicules form along the lateral margin. These tiny spikes are gradually driven into the dermis, the deeper layer of skin next to the nail, with every step you take. Walking, running, and the pressure from your shoes all push the spicule deeper.
Once the nail breaks through the skin, your immune system responds the same way it would to a splinter. The area becomes red and swollen, and fluid builds up around the wound. If bacteria enter through the break, you’ll see pus and the skin may become warm to the touch. Left alone long enough, the irritated tissue can form a mound of raw, bumpy tissue called granulation tissue that bleeds easily and grows over the nail edge.
The Most Common Causes
Cutting Your Nails Wrong
This is the single most frequent trigger. Rounding the corners of your toenails or cutting them too short leaves a small edge of nail hidden below the skin fold. As the nail grows forward, that edge has nowhere to go but into the surrounding tissue. The American Academy of Dermatology recommends cutting straight across, keeping the nail roughly even with the tip of your toe. A good technique is to make the first cut slightly off one side to create a straight edge, then follow that line across to the other side.
Shoes That Squeeze Your Toes
Footwear with a narrow toe box pushes the skin fold against the nail edge with every step. Over time, this constant pressure forces the nail plate out of its groove, creating the break in the skin that starts the inflammatory cycle. High heels, pointed dress shoes, and athletic shoes that are a half-size too small are all common culprits. If your toes feel compressed when you press down during a stride, your shoes are contributing.
Trauma and Repetitive Impact
Stubbing your toe hard can crack or shift the nail plate enough to redirect its growth into the skin. But you don’t need a single dramatic injury. Repetitive micro-trauma from running, kicking a soccer ball, or any activity that jams your toes against the front of your shoe does the same thing over many weeks. Runners and soccer players are especially prone to ingrown nails on the big toe for exactly this reason.
Sweat and Moisture
Excessive sweating softens the skin fold around the nail. When that tissue is soft and waterlogged, it takes very little force for a nail spicule to pierce through it. This is why ingrown toenails are more common in teenagers (whose feet sweat more), in warm climates, and in people who wear non-breathable shoes for long stretches.
Your Nail Shape
Some people inherit nails that naturally curve more than average. Pincer nails, which roll inward on both sides like a tube, are one hereditary variant that makes ingrown nails almost inevitable without careful management. If your parents or siblings deal with recurring ingrown nails, your nail morphology is likely a contributing factor. Fan-shaped nails that widen at the tip can also crowd the nail groove, especially in tighter shoes.
How It Progresses
Ingrown toenails follow a fairly predictable path. In the earliest stage, you’ll notice mild tenderness along one side of the nail, with slight redness and a bit of puffiness in the skin fold. Pressing on it hurts, but it’s manageable. Many people catch it here and resolve it with a change in footwear and proper trimming.
If it continues, the pain intensifies and you’ll start to see drainage. The skin becomes more swollen, warm, and visibly red. Clear or yellowish fluid may seep from the edge, signaling that infection has set in. At this point, soaking the foot and gently lifting the nail edge with a small piece of clean cotton can sometimes redirect the nail’s growth, but the window for home care is narrowing.
In the most advanced stage, the swelling and infection worsen significantly. Granulation tissue forms over the nail margin, creating a red, raw mound that bleeds on contact. The pain can make wearing any closed shoe difficult. This stage typically requires professional treatment, which may involve removing part of the nail border or treating the nail root to prevent regrowth along that edge.
Why Diabetes Makes It More Dangerous
For most people, an ingrown toenail is painful but not serious. For people with diabetes, the stakes are considerably higher. Nerve damage in the feet (neuropathy) can mask the early pain signals, meaning the nail digs deeper and infection advances before anyone notices. Poor circulation slows healing, giving bacteria more time to spread. An untreated infection can move into surrounding tissue or bone, and in severe cases, restricted blood flow to the infected area can cause tissue death. This is why even a minor toenail issue in someone with diabetes warrants prompt attention.
How to Prevent Them
Most ingrown toenails are preventable with a few consistent habits:
- Cut straight across. Resist the urge to round the corners or follow the curve of your toe. Leave the corners slightly visible above the skin fold.
- Don’t cut too short. The nail should be roughly even with the tip of your toe. Cutting below that line exposes the nail groove and lets the regrowing edge dig in.
- Wear shoes that fit. Your toes should be able to wiggle freely. If you’re buying athletic shoes, leave about a thumb’s width between your longest toe and the front of the shoe.
- Keep feet dry. Moisture-wicking socks and breathable shoes reduce the softening of skin that makes penetration easier. Change socks if your feet sweat heavily during the day.
- Protect your toes during sports. If you run or play a kicking sport, make sure your shoes fit well and your nails are trimmed before activity. Steel-toed boots help if your work involves heavy objects near your feet.
If you’ve already had one ingrown toenail, you’re more likely to get another on the same toe. Paying attention to how you trim that nail and what shoes you wear on active days makes the biggest difference in breaking the cycle.