onychorrhexis onychorrhexis onychorrhexis (from the greek words ὄνυχο- ónycho-, "nail" and ῥῆξις rhexis, "bursting"), is a brittleness with breakage of finger or toenails that may result from hypothyroidism, anemia, anorexia nervosa or bulimia, or after oral retinoid therapy.: 786 it can also be seen in melanoma that involves the nail and onychomycosis. onychorrhexisother namesbrittle nailsspecialtydermatology onychorrhexis affects up to 20% of the population.: 786