Nails. We often don’t think about them unless we develop a hangnail or decide that they need a color change in the form of a manicure. However, our nails can provide clues for systemic diseases and we should keep an eye out for any changes can be beneficial to our health. Some nail disorders can be easily fixed, but others are worth checking for a more serious illness.
1) Brittle Nails: Peeling and Crumbling
Brittle nails are weak nails that often split, peel, flake, or crumble. While this can occur in older patients, brittle nails are more common in women than in men.[3,4] These weak nails can be due to vitamin deficiency and the brittle nails usually improve with supplemental biotin and oral bioactive collagen peptide. Topical retinoids have also helped improve the nail surface area; your care provider can help determine which treatment plan is best for your nails.
2) Pitting: Dents in the Nails
Pitting refers to small dents or pits that occur in the nail bed. These small notches in the nail bed commonly occur in patients with psoriasis. However, they can occur in other skin conditions and very often can occur without a clear reason or disease. While oral and injectable medications can help improve symptoms of pitting nails associated with psoriasis, steroids, and vitamin D analogs can be helpful as well.
3) Onycholysis: Premature Nail Lifting
Onycholysis is where the nail plate separates from the nail bed. Often referred to as “plummer’s nail,” onycholysis can be related to nail damage caused by systemic conditions including chronic inflammatory diseases and thyroid disease. As onycholysis can have multiple causes, treating the underlying disease can help best improve the loss of nails. In patients with onycholysis due to psoriasis, treatment with a topical vitamin D derivative and steroid combination helped to improve nail appearance and growth.
4) Dark Streaks on the Nail: Watch out for Melanoma
Color variations, such as a dark streak on the nail, can prompt a trip to the doctor. Dark green pigmentation on the nails can be due to a bacterial infection such as Pseudomonas aeruginosa or Proteus. Bleeding underneath the nails can appear as dark spots due to a single instance of injury or multiple, repeated instances of smaller injuries, such as on the toenails. However, sometimes a darker pigment streak, known as melanonychia, can be a sign of a type of skin cancer called melanoma. Therefore, dark streaks on the nails should warrant a visit to your dermatologist in order to distinguish benign cases from cancer.
5) Beau’s Lines: A Sign of Stress
Beau’s lines are parallel lines that run from the two sides of the nail in alternating ridges and grooves. They are often caused by trauma, high fevers, chemotherapy, and Raynaud’s disease, but can occur with any systemic condition.[1,13,14] Usually, the depth and width of Beau’s lines can indicate the severity and duration of an illness. The appearance of lines can help determine when a disease process may have started as nails grow approximately 1 mm every 6-10 days.[15,16] If you have these grooves in your nails, it’s important to speak with your healthcare provider to exclude systemic diseases.
6) Koilonychia: A Sign of Inflammation or Nutritional Deficiency
Also known as “spooning” of nails, Koilonyhcia is where the nails curve upward like a spoon. The nails are physically curved with raised ridges. These curved nails can be a sign of inflammation in the body such as lichen planus or psoriasis, but also can be related to nutritional deficiencies such as anemia from low iron levels.[18-20]
7) Terry’s Lines: A Change in Nail Blood Flow
The nails appear white except for a narrow band of pink near the tip of the nails. Terry’s nails can be related to aging as well as other underlying disease processes. Terry’s nails are attributed to changes in the blood flow in the fingers as well as overgrowths of connective tissue, liver scarring, chronic kidney failure, and inadequate heart function.
8) Yellow Nails
Yellow nails occur when the nails grow more slowly than normal, becoming thick and pulling away from the nail bed. While the exact cause is not well understood, yellow nails can be linked to respiratory problems and swelling of legs and arms. Most patients who experience yellow nail syndrome are middle-aged, but the condition can occur in children as well.  Exposure to titanium is thought to play a role in developing yellow nail disease. In one case, a child who had swallowed titanium toothpaste later developed yellow nail syndrome.[23,24]
Clubbing is where the nail thickens and curves around the fingertips, a process that takes years to acquire. Sometimes these nails and the finger changes can be referred to as “drumstick fingers” because of their appearance. This nail disease is often a sign of an underlying disordered process such as the formation of excessive blood vessels. While more common in women than men, clubbing can occur as a result of systemic diseases that affect the oxygen flow to distal body areas such as cystic fibrosis, heart disease, lung cancer, and autoimmune diseases. In clubbing, the treatment of these nails usually involves treating the underlying disease.