Thickened toenails are commonly caused by aging and injuries that lead to fungal infections, according to Footsmart. As people age, their toenails become thicker, while injuries can cause the toenails to split. Both conditions make the toenails more prone to fungus, leading to additional thickness and yellowing of the nails.
Thick toenails can also be caused by ill-fitting footwear that cause excessive pressure on the toes, as well as medical conditions such as psoriasis and diabetes, so it is always best for individuals with unexplained thickened toenails to consult with a podiatrist to obtain an accurate diagnosis, explains Healthy Feet Store. Treatments for the condition include trimming or grinding of the nails, fungal medications and surgical removal.