Final answer:
Ingrown toenails are often caused by improper trimming, tight footwear, injury, naturally curved toenails, and dermatophytic skin infections like athlete's foot.
Step-by-step explanation:
Some common causes of ingrown toenails include improper nail trimming, where nails are cut too short or not straight across; tight footwear or socks that place excessive pressure on the nails; injury to the toenail; and having naturally curved toenails. Additionally, dermatophytic skin infections such as athlete's foot or fungal infections can weaken and deform the nail, making it more susceptible to becoming ingrown. To prevent ingrown toenails, it is recommended to wear properly fitting shoes, maintain good foot hygiene, and trim nails straight across.