Brittle nails can be a normal result of aging. Or they can indicate a medical abnormality. Here is a list of things that can cause your nails to be brittle, weak and break easily, courtesy of the U.S. National Library of Medicine:

-- Frequent use of nail polish, remover, hardeners or other cosmetic nail applications.

-- Reduced amounts of zinc or iron in the body.

-- Problems with the thyroid.

(HealthDay News)