What visual characteristics differentiate a healthy nail from an unhealthy nail?

Healthy nails display visual characteristics that reflect their well-being. They are typically smooth, which means they do not have any ridges, bumps, or indentations. This smoothness contributes to a healthy appearance and is indicative of proper nail growth and care. Consistency in color is another important aspect; healthy nails usually show a uniform shade that doesn't contain any discoloration, spots, or streaks that might signal a problem.

In contrast, the other options describe characteristics that are commonly associated with unhealthy nails. For example, thick and dark nails may be a sign of fungal infections or other conditions. Rough surfaces and dull finishes often indicate damage or neglect. Lastly, being brittle and fragile is a sign of weakness in the nail structure, usually leading to breakage and other issues. These characteristics contrast sharply with the features of healthy nails that are smooth and maintain an even color throughout.