Ohio State Board Nail Technician Practice Exam - Prep, Study Guide & Practice Tests

Ingrown nails are when nails grow into the skin, causing pain and sometimes infection. Cutting nails too short (choice A) or applying too much polish (choice B) can both actually encourage the nails to grow outwards instead of into the skin and are not common causes of ingrown nails. Wearing tight shoes (choice D) can create pressure on the toes that may contribute to ingrown nails, but it is not the direct cause. Filing too deeply to the corners (choice C) is the most common cause of ingrown nails as it can create a sharp edge that can pierce into the skin and cause the nail to grow into the skin. It is important to file nails straight across instead of rounding the corners to prevent this from happening.