What is a common symptom of nail fungal infections?

Discoloration of the nail is a common symptom of nail fungal infections due to the way fungi affect the nail structure. Fungal infections may cause the nail to change color, appearing yellow, brown, or even greenish. This discoloration occurs as the fungi invade the nail bed, leading to a buildup of debris and a change in the nail's natural appearance.

The other options do not typically indicate a fungal infection. Increased shine is not a symptom associated with fungal growth; instead, nails may look dull or damaged. Growth of artificial nails is unrelated to infection and pertains more to nail enhancement products rather than health. Flat nails may result from various other conditions but are not indicative of a fungal infection specifically. Thus, discoloration stands out as the primary symptom to recognize.