Thickening of the thumbnail of the foot may be caused by nail aging, nail fungus disease, and nail malnutrition. 1. Nail aging: with age, the metabolism will slow down, if you do not pay attention to clean up the secretion, may cause cuticle stagnation, resulting in nail thickening. 2. Nail fungus disease: mainly caused by skin fungus infection, may cause nail thickening, gray and yellow nails, cloudy, uneven nail plate, as well as nail thickening and other symptoms. 3. Nail dystrophy: mainly due to a variety of reasons may be and congenital factors, genetic factors, disease factors, drug stimulation and other factors caused by nail roughness and atrophy, the nail plate loses its luster, nail thickening and other symptoms. Foot thumb nail thickening, there may be other reasons, should go to the hospital in a timely manner to check, clarify the cause of treatment as prescribed by the doctor.