Thickened and crumbly nails may be caused by nail fungus disease, pemphigus and chronic eczema. 1. Nail fungus disease: caused by fungal infection, usually easier to be triggered when there is nail trauma. It is characterized by thickening of the toenails, uneven surface, loss of luster, debris under the nails, and pain and discomfort in severe cases. 2. Patchy baldness: If the nails are thickened with white residue inside, the nail cap is rough, turbid, lusterless, longitudinally bulging, and the nail cap is separated from the nail bed with patchy baldness, it can be regarded as nail damage caused by patchy baldness. 3. Chronic eczema: Chronic eczema that is severe and remains untreated for a long period of time may also affect the nail plate, resulting in abnormal nail plate growth, thickened nails, and internal debris. Nail thickening with debris may be caused by other factors, it is recommended that patients go to the hospital in a timely manner, to clarify the cause of the disease, and follow the doctor’s instructions to standardize the treatment.