There are many causes for thick toenails other than toenail fungus. Thick toenails may also be due to psoriasis or type 1 or 2 diabetes. Sudden or repeated trauma or injury to the toenails due to sports activities (e.g., running, dancing, etc.) can also cause toenails to thicken, as well as ill-fitting shoes.
Psoriasis is an autoimmune disease that causes red, scaly patches on the skin, but it can also cause nail thickness for both the hands and feet. If psoriasis is the cause of your nail thickness, you are likely to develop ridges on the nails, and the nails may loosen and separate from the nail bed.
Additionally, aging can cause your toenails to thicken.
Over time as the toenails get thicker, you might start experiencing some symptoms, such as
As for the appearance, the nails may take on a yellow, green, or brown hue and start looking gnarly or have some scaling on the surface.