Your fingernails can reveal a lot about your health. “Brittle, weak, and peeling nails are more often the result of a poor diet than of systemic disease,” says Dr. Sara Norris. But if nail changes persist or come with symptoms like fatigue, weight loss, or swelling, see a doctor.

**Beau’s lines**—deep grooves across the nail—may appear after serious illness or trauma. “Some people developed Beau’s lines after they had COVID-19,” notes Dr. Bhavini Shah. They can also be caused by chemotherapy, infections, or zinc deficiency.

**Clubbing** is when nails curve downward and fingertips swell. It may signal lung or heart disease. Shah explains, “If you notice red or purple lines under your nails without injury, it could be heart-related.”

**Spoon nails** (koilonychia) curve inward and often suggest iron-deficiency anemia. “This condition is common after pregnancy,” Shah says, and is treatable with iron-rich foods or supplements.

**Nail pitting**—tiny dents—can result from psoriasis or eczema. Meanwhile, **dark streaks** under the nail could be melanoma, a serious skin cancer. Always get suspicious changes checked early.

**Terry’s nails**, where most of the nail turns white, may be linked to liver disease, aging, or other chronic illnesses.