Small toenails become yellow and thickened protruding may be related to onychomycosis, thick nail disease, toenail aging, etc.. 1. ringworm of the nail: caused by fungal infections, most of which are directly transmitted by tinea pedis, can lead to nail plate yellowing, thickening, brittleness and so on. 2. Thick nail disease: congenital thick nail disease is a hereditary disease, for autosomal dominant inheritance, the performance of the toenail significant hypertrophy. Acquired acromegaly is mostly secondary to other diseases, and may appear as thickening and extreme hardness of toenails, which will gradually turn yellow. 3. Toenail aging: this is mostly seen in the elderly in the young often barefoot labor, it will cause damage to the toenails, with the increase in age will occur aging phenomenon. Performance for the toenail easy brittle, thickened yellow, and even toenail deformity and other symptoms. Small toenail yellowing and thickening protruding can also be seen in other causes, it is recommended to consult a doctor in a timely manner, in accordance with the doctor’s instructions for the relevant examination, in the doctor’s help to clarify the cause, and targeted treatment or treatment.