Cracked or Split Nails

Dry, brittle nails that frequently crack or split have been linked to thyroid disease. Cracking or splitting combined with a yellowish hue is more likely due to a fungal infection.
Puffy Nail Fold

Chronic paronychia is a condition that causes inflammation, redness, tenderness, and swelling of the skin folds and tissues surrounding the nails. It is usually the result of irritants or allergens but it can be caused by the fungus Candida albicans, other infections or psoriasis. It can usually be treated with topical steroids.
Dark Lines Beneath the Nail

This nail discoloration is called a melanonychia and is caused by the pigment melanin. There are several possible causes including skin cancer, infection or injury.
Gnawed Nails

Biting your nails may be nothing more than an old habit, but in some cases it’s a sign of persistent anxiety that could benefit from treatment. Nail biting or picking has also been linked to obsessive-compulsive disorder. If you can’t stop, it’s worth discussing with your doctor.
Nails Are Only Part of the Puzzle

Though nail changes accompany many conditions, these changes are rarely the first sign. And many nail abnormalities are harmless — not everyone with white nails has hepatitis. If you’re concerned about the appearance of your nails, see your doctor or a dermatologist.