What is an Ingrown Toenail?
An ingrown toenail is a nail that has curved downward and grown into the skin at the border of a toenail. If an ingrown nail breaks through the skin, it can cause bacteria to enter and may cause an infection. 

What Causes Ingrown Toenails?
Ingrown toenails can occur by any variety of reasons, from being genetically inclined, to trauma or impactful activities like kicking or running. The most common cause, however, is improper nail trimming. Cutting your nails too short encourages the skin near the nail to fold over the nail, where the nail will continue to grow and possibly cause pain, discomfort, redness, swelling, and warmth. Certain nail conditions, like a fungal nail infection, or losing a nail to trauma, can also cause ingrown toenails.