Complex sentence: Treatment of onychomycosis is challenging because the infection is embedded within the nail and is difficult to reach; full removal of symptoms is slow and may take a year or more, since new nail growth must entirely replace old, infected growth.
Split into simpler sentences: Treatment of onychomycosis is challenging because the infection is embedded within the nail and is difficult to reach. It may take a year or more, since new nail growth must entirely replace old, infected growth.