The symptom of big toe nail cap separating from the flesh is medically known as nail separation, which can be caused by a variety of factors, commonly including trauma, disease and so on. 1. Trauma: When the toenail is hit locally by external force, it can lead to bruising under the nail plate, resulting in separation from the nail bed. When the toes are squeezed and produce subnail hematoma, the nail plate can be pushed up. 2. Disease: common for onychomycosis. The fungus invades the nail plate, resulting in a gap between the nail plate and the nail bed, resulting in separation. In addition, can also be seen in the human papilloma virus infection around the nail, resulting in common warts under the nail, can be the top of the nail plate. These are some of the possible causes of nail separation, and it is recommended that you seek medical attention in time to be diagnosed by a medical professional.