When a toenail is classified as “ingrown,” it can cause extreme pain when the person puts weight on the affected toe. This condition is when a nail starts digging into the sides of the toe, growing into the soft tissue and causing a wound to start forming. If an ingrown toenail is left untreated, it may lead to long-term discomfort and pain, possibly even causing an infection because of the bacteria that linger in socks and shoes.