Why doesn't OTC topical medications help?

Topical medications are ineffective in most cases, because the infection starts growing under the nail. No topical medicines penetrate deep enough into and through the nail, to treat the living organisms under the nail plate. Any clearing of the nail surface is eventually overtaken by infected nail replacing it from underneath. Unfortunately, in this condition, any self-treatment is, at best, temporary. Use of a topical antifungal medicine may, at best, prevent spread of the fungus to, as yet, unaffected nails or the surrounding skin.