These conditions can look similar in photographs, which is why an image alone cannot reliably identify the cause.

What Are Beau’s Lines?

Beau’s lines are horizontal depressions that extend across the nail.

They occur when nail growth is temporarily slowed or interrupted at the nail matrix—the area beneath the skin at the base of the nail where the nail is produced.

Think of the nail as a timeline.

Something happens to the body → nail growth is temporarily disrupted → the nail continues growing → the previous interruption eventually becomes visible as a horizontal groove.

Because fingernails grow slowly, the position of a line can sometimes provide an approximate clue about when the underlying event occurred.

However, the line itself doesn’t tell you exactly what caused it.

What Can Cause These Nail Grooves?

There are many possibilities.

A temporary interruption in nail growth can occur after:

• A significant infection or high fever
• Major physical stress
• Severe illness
• Surgery