The eyes may be the windows to the soul, but your fingernails could be the door to your health. They can open the secrets to overall health status, as well as provide clues to conditions or diseases you may not know you have. But Dr. Jeffrey Linder, chief of internal medicine and geriatrics at Northwestern University Feinberg School of Medicine in Chicago, says that some nail changes are simply the result of aging, so “it’s important not to get alarmed if you see something abnormal,” he says.

Nail changes to watch for:

• Lunula color. According to AARP, nails have a white half-moon shape at their base, just above the cuticle. A change in color or size could indicate an underlying disease. For example, if the lunula extends almost to the top of the nail, making the majority of the nail white, it could be a sign of cirrhosis of the liver, chronic renal failure or congestive heart failure. 

• Yellow nails. One of the most common causes of yellow nails is a fungal infection, says WebMD. As the infection worsens, the nail bed may contract, and nails could thicken and crumble. In rare cases, yellow nails could indicate severe thyroid disease, lung disease or diabetes.

• Ripples. If the nail surface is rippled or pitted, this could be an early sign of inflammatory arthritis. The skin under the nail might also appear reddish-brown.

• Gnawed nails. A nail-biting habit may point to an underlying anxiety disorder or obsessive-compulsive disorder. If you can’t stop biting your nails, consult a healthcare professional, says WebMD.

• Lines. If there is a dark-colored streak that runs down the length of your nails, this could be a sign of melanoma, the deadliest form of skin cancer. See your doctor or dermatologist right away if you notice this sign.

• Clubbing. Nail clubbing occurs when the tips of the fingers enlarge and the nails curve around the fingertips, usually over the course of years, says the Mayo Clinic. Nail clubbing could indicate low oxygen in the blood triggered by various types of lung disease. Nail clubbing is also associated with inflammatory bowel disease, cardiovascular disease, liver disease and AIDS.

• Pitting. Ice-pick like depressions in the nails are called nail pitting and are common in people who have psoriasis. Nail pitting is also be associated with connective tissue disorders, such as alopecia areata — an autoimmune disease that causes hair loss.

• Beau’s lines. These are indentations that run horizontally across the nails and are linked to uncontrolled diabetes and peripheral vascular disease, as well as illnesses associated with high fever, such as scarlet fever, measles, mumps, and pneumonia. Beau’s lines are also a sign of zinc deficiency, says the Mayo Clinic.

• Blue hue. Nails that appear bluish may be a warning sign of COVID-19 says AARP. Linder says that this could indicate low levels of oxygen in the blood. The Centers for Disease Control and Prevention recommends that anyone who has this symptom seek immediate medical care.

• Brittle nails. If your nails are thin and brittle, this may signal a thyroid disorder. But it may be that they just need a little more TLC. Wear gloves when you do the dishes or clean with chemicals than can affect your nails. Another way to keep your nails healthy is to eat a well-balanced diet.