The most common cause of thick toenails is a fungus infection similar or identical to the fungus that causes “athlete’s foot.” The nail usually takes on a yellowish color and may be difficult to cut. The problem usually becomes painful when closed shoes are worn since the thick nail is pressed down into the skin underneath.
Although the big toe (hallux) is most commonly infected, the nails of the other toes are also often involved. In some cases, this problem may be best treated with oral and/or topical anti fungal medicine.
New Laser Therapy is now used to treat more resistant Fungus Toenails.