What can cause discoloration of the nails?

Discoloration of the nails can indeed be caused by nail polish stains. Over time, certain pigments in nail polishes can adhere to the nail plate, particularly if the polish is darker in color or if it is left on for extended periods without a base coat. The base coat acts as a barrier to prevent such staining; however, if not used, or if the polish is applied directly to the natural nail, staining can occur. This condition is typically superficial and can often be resolved by proper nail care, including the regular use of base coats and proper polish removal techniques.

Other factors mentioned, such as dietary changes, excessive nail filing, and allergies to polish, can also affect the health and appearance of nails, but they are less commonly recognized as direct causes of discoloration. Dietary changes may affect nail health, potentially leading to changes in growth or texture but are not typically associated with noticeable discoloration. Excessive filing may lead to thinning or weakening of the nails but does not specifically cause staining. Allergic reactions to polish might result in redness, swelling, or peeling rather than visible discoloration. Thus, nail polish stains are a more definitive cause of nail discoloration.