The most common causes for the loss of a toenail include injury and infection, explains Foot Vitals. Dermatophytes, a contagious fungal infection, feeds upon keratin in nails.
Activities such as skating, running, skiing and playing soccer sometimes cause injuries that result in the loss of a toenail, according to Foot Vitals. Vigorous activity and pressure on shoe gear can result in blistering under the nail that causes the nail plate to separate.
Symptoms of a toenail that breaks or falls off due to injury include a collection of blood under the nail, discoloration and bleeding, explains Foot Vitals. An infection of the nail causes yellow, green or brown discoloration, pain, swelling and thickening of the nail.