The most common cause of yellowed, thick and/or deformed toenails is a fungal infection of the toenail. The fungus that infects the nail, most commonly, is the same fungus that causes athletes foot. Fungal infections occur when microscopic fungi gain entry through a small trauma in the nail, then grow and spread in the warm, moist environment inside the patient's socks and shoes. It tends to be slowly progressive, damaging the nail to a greater and greater degree over time. The infection usually starts at the tip of the nail and works its way back.
Fungal infections can affect the fingernails as well as the toenails, but toenail fungus is more difficult to treat because toenails grow more slowly. A single toenail or any number of nails can be affected.
Toenail fungus can be picked up in damp areas such as public gyms, shower stalls or swimming pools, and can be passed among family members. Athletes and people who wear tight-fitting shoes or tight hosiery that cause trauma to the toes or keep the feet from drying out are at higher risk. The condition can also spread from one toe to another. Other risk factors include abnormal PH level of the skin, not drying off the feet thoroughly after bathing or exercise, and a compromised immune system in someone who has been exposed to a fungus. You have an increased risk developing a fungal nail infection if you have various other conditions. For example: diabetes, psoriasis, poor circulation or a general poor state of health.
Because it is difficult to treat or eradicate toenail fungus, it is a good idea to try to prevent it. It helps to wear protective shoes or sandals in public showers, pool areas and gyms, and to avoid borrowing someone else’s shoes or sharing socks or towels with someone who has toenail fungus. Wash your feet regularly, and dry them thoroughly when they get wet. Wearing nail polish on the toes is not advised because it can seal in fungus and allow it to grow. Keep toenails trimmed, and be sure to disinfect any pedicure tools before using them.