What might cause excessively thick toenails only on your big toe? healthy male subject, smoker, turkish descent

Probably : Probably the most likely is fungal infections but many conditions can cause thickening of the toenail(s) such as eczema, psoriasis, chronic trauma, and fungal infections to name a few. This is difficult without seeing the nail itself. I would typically evaluate the nail for its characteristics such as color and texture of the nail to help make a diagnosis. Often, i will take a sample of the nail for culture to see if there is any fungal infection and sometimes perform a nail clipping for biopsy if the diagnosis remains elusive. I hope this helps a little.

Fungus or trauma: More than likely it is due to a fungus or trauma or both. It could be due to a number of other possible reasons though. Get the feet inspected by a professional to determine the cause of the problem, as treatment varies depending on the diagnosis.

Fungus would be a: Possibility. Biomechanical condition called hallux limitis can cause the toenail to rub against the shoe as well causing thickness of the toenail in the process.....A podiatrist should be able to rule out the differential diagnosis and give you a diagnosis and treatment plan.