How it worksonce they have established themselves under a toenail or fingernail dermatophytes fungi feed on keratin which is the substance that makes up the structure of the nail left untreated the nailrsquos condition will worsen and it will gradually change appearance first white patches appear then the nail turns yellow starts to thicken and eventually crumblesexcilorreg fungal nail infection is able to penetrate the nail and modify its microenvi