Yes, a toenail infected with a fungus is contagious.  Fungus is a living organism and may live on the surface of the skin causing athlete's foot type symptoms, and often the condition of the surrounding environment can exacerbate the condition.  The fungus can be transmitted from places where you might go barefoot such as locker rooms, the side of a pool, a gym mat, or wearing some one else's shoes who have the infection.  It may also be transmitted from nail salons due to unsanitary instruments or from the nail polish bottle used on multiple people.  (We carry Dr's Remedy nail polish at our office, so you can bring your own bottle every time.) Once the fungus invades your toenail, it thrives and may spread to the other nails unless treated.  If you think you may have a fungal nail, make an appointment with one of our doctors sooner than later.  So treat the nail before it has a chance to spread to other nails, the other foot, or even to other people, and early treatment gives you the optimum chance for success.