Keep your feet clean Dry can stop your fungus growing or spreading. These are some guidelines for Kerassentials Customers to get the most from this product. Kerassentials is 100% safe, as it is all-natural. Undecylenic acid works to kill the toenail fungus and prevent regrowth while tea tree and lavender oil soothe the skin. Most fungi are harmless unless they penetrate the skin." This usually requires that the nail has been damaged by trauma or infection. Fungi thrive best in moist, warm environments. Touching infected surfaces on your feet can also lead you to contracting toenail and nail fungus. The medicated nail paint is applied to the nail and should remain on the nail for approximately a week. However, it has a lower rate of cure than oral medications.