Which factor is a common cause of nail discoloration?

The use of dark nail polish without a base coat is a common cause of nail discoloration because darker pigments can stain the nail plate. When a base coat is not applied, the chemicals and dyes present in the dark polish can penetrate the surface of the nail, leading to yellowing or other discoloration. This is especially true for prolonged wear or repeated application of dark colors without sufficient barrier protection that a base coat provides. A base coat helps to create a protective layer, minimizing the risk of staining and maintaining the natural color and health of the nail beneath.

In contrast, frequently washing hands, excessive trimming of nails, or improper drying techniques do not typically contribute directly to nail discoloration in the same manner as a lack of base coat does. Frequent handwashing can cause dryness or brittleness, excessive trimming may lead to nail breakage or injury, and improper drying could contribute to other issues like fungal infections or peeling but is not a direct cause of discoloration like dark polish without protection.