Thickened and bulging bunion nails can be caused by onychomycosis, nail dystrophy, and pestle and mortar nails. 1. Tinea cruris, also known as gray toenail, is caused by a fungal infection of the feet big toe nails become thick and bulging, there will also be a nail yellow, brittle, and the nail plate is often accumulated under the fine powdery material. 2. Nail malnutrition: due to the lack of vitamins and trace elements in the body, resulting in the thickening and bulging of the toenail of the big toe and loss of luster. 3. Pestle-shaped nails: common in iron deficiency anemia, chronic cardiopulmonary diseases, cirrhosis and other diseases, the normal angle of the nail frontal disappeared, in the shape of a pestle, the nails become thick and bulging. There may be other reasons for the thickening and bulging of the toenail of the big toe. It is recommended that you go to the hospital in time to improve the examination and clarify the cause of the disease, and then give targeted treatment or therapy.