Your fingernails and toenails can tell you more about your health than you might think. New nail changes in color and texture can be clues to an underlying condition — including some heart diseases. For example, horizontal red lines under the nails have been linked to certain heart problems and other health conditions.

In this article, we’ll explore what horizontal red lines under your nails could mean and what other nail changes might point to a heart issue. If you notice something unusual, it’s a good idea to talk to your cardiologist (heart doctor) or a dermatologist (skin doctor).

Understanding Nail Anatomy

Before diving into different nail conditions, it helps to first understand nail anatomy. The hard part of your nail that you can see — the nail plate — starts growing from under the skin at the nail root. As new cells form, they push older ones forward. The older cells flatten and harden as they move out due to keratin, a protein that gives nails their strength.

Beneath the nail plate is the nail bed, which contains capillaries (tiny blood vessels) that bring oxygen and nutrients to the nail to help it grow. Because of this blood supply, nail changes can sometimes reflect what’s happening in your body — including your heart.

Are Horizontal Red Lines a Sign of a Heart Condition?

Red lines under the nails — known as erythronychia — are often harmless and have no known cause. Some people have natural discoloration of their nail plates. However, in some cases, horizontal red lines could be a sign of an underlying condition.

One case study reported in the journal Dermatology and Therapy described a 64-year-old man who had horizontal red lines on six fingers. He had no known history of heart conditions, but his doctors noted that the lines could be a sign of a rare condition called amyloidosis.

Amyloidosis occurs when abnormal amyloid proteins clump together and collect in organs. Cardiac amyloidosis is a form of heart failure that occurs when these proteins collect in the heart and cause the heart wall to thicken. Amyloidosis also affects the heart’s electrical connections, causing irregular heart rhythms. The buildup of amyloid proteins can also block heart valves and blood flow.

It’s important to keep in mind that horizontal red lines aren’t the most common sign of cardiac amyloidosis. Other symptoms include:

• Shortness of breath
• Palpitations (fast or irregular heartbeats)
• Liver or kidney problems
• Swelling in the ankles, feet, and abdomen due to fluid buildup
• Fatigue (persistent exhaustion that doesn’t improve with rest)

Be sure to tell your doctor if you notice any of these symptoms along with red lines beneath your nails.

Are Other Nail Changes Linked With Heart Disease?

Although horizontal red lines aren’t commonly linked to heart disease, other nail changes might be. Doctors and researchers have found that other nail disorders can appear alongside heart problems. These nail abnormalities include splinter hemorrhages, Beau’s lines, and Mees’ lines.

Splinter Hemorrhages

Splinter hemorrhages are thin, red or brown, vertical lines underneath the nails. They look like tiny splinters of wood, which is how they got their name. These lines form when capillaries break or leak a small amount of blood.

Most people get splinter hemorrhages after injuring a nail. The lines usually fade as the injury heals and the nail grows out.

Sometimes, splinter hemorrhages may be a sign of a more serious health condition, such as endocarditis, a rare but serious heart infection. Endocarditis occurs when bacteria get into the bloodstream and infect the endocardium — the inner lining of the heart and its valves. If untreated, endocarditis can damage the heart. Between 15 percent and 33 percent of people with endocarditis also develop splinter hemorrhages.

Other symptoms of endocarditis include:

• Chest pain when breathing and shortness of breath
• Fever and chills
• Swelling in the abdomen, legs, or feet
• Fatigue
• Muscle aches and joint pain

Splinter hemorrhages can also be associated with other underlying medical conditions such as lupus or psoriasis. Blood-thinning medications, such as aspirin and warfarin, can also cause these nail changes.

Beau’s Lines

Horizontal white or skin-colored grooves known as Beau’s lines often appear on fingernails and toenails after serious physical stress, such as a major illness or health event. When your body is focused on healing, it may pause or slow down nail growth — and Beau’s lines are the result.

Beau’s lines may appear after a heart attack or an illness that causes high fevers, such as pneumonia, measles, mumps, or a strep infection. These nail changes may also show up in people with long-term (chronic) health conditions, including:

• Peripheral arterial disease, a circulation problem in which blood flow to the limbs is reduced
• Diabetes mellitus, a condition that can lead to high blood sugar levels, which may affect blood flow and nail health
• Autoimmune diseases, in which the immune system mistakenly attacks healthy body tissues
• A deficiency of zinc, a mineral that’s needed for healthy skin and nails

If you notice Beau’s lines and haven’t recently been sick or stressed, it’s worth bringing up with your doctor to see if further testing is needed.

Mees’ Lines

Mees’ lines — white, horizontal lines that run the width of a nail — usually start near the cuticle (the base of the nail) and move toward the top of the nail as it grows. Mees’ lines were originally linked with poisoning from exposure to heavy metals such as arsenic, selenium, and thallium. Doctors and researchers now know that Mees’ lines also affect people with other medical problems, including heart failure.

In heart failure, the heart muscle is too weak to pump oxygenated blood effectively. When this happens, the body doesn’t get enough oxygen, which can cause symptoms like fatigue, swelling, and shortness of breath. The stress heart failure places on the body can affect nail growth, which may lead to Mees’ lines.

One case report described a 49-year-old man who was hospitalized for heart failure and developed Mees’ lines soon afterward. The lines grew out over four months and eventually disappeared.

Mees’ lines have also been linked with a variety of other conditions, such as altitude sickness, carbon monoxide poisoning, certain cancers including Hodgkin lymphoma, and kidney failure. Most of the time, Mees’ lines don’t need treatment and will grow out naturally. However, it’s important to treat the underlying cause of this symptom. For example, proper medication and lifestyle changes are key to managing heart failure.

Do Horizontal Red Lines Affect Nails for Other Reasons?

There’s not much research on what horizontal red lines could mean for health. However, the authors of the case study of the 64-year-old with lines on six fingernails suggested that — based on his medical history and other research — red horizontal lines could be linked to:

• Tumors, either benign (noncancerous) or malignant (cancerous)
• Inflammatory skin conditions such as lichen planus, which causes flat, purple, gray, or brown bumps
• Graft-versus-host disease, a condition that can happen after a stem cell transplant
• Other nail conditions that affect the nail bed

More research is needed to understand the link between horizontal red lines under nails and certain medical conditions.

Talk to Your Doctor About Nail Changes and Your Health

If you notice any new horizontal red lines or changes in your nails’ color or texture, talk to your doctor. These changes may be harmless, but they could also indicate a serious health issue. Be sure to tell your doctor or dermatologist if you also have other symptoms. Together, you and your healthcare provider can figure out what’s causing your nail issues and come up with a management plan that best fits your needs.

Talk With Others Who Understand

MyHeartDiseaseTeam is the social network for people with heart disease and their loved ones. On MyHeartDiseaseTeam, more than 62,000 members come together to ask questions, give advice, and share their stories with others who understand life with heart disease.

Do you have horizontal red lines under your nails? Have you noticed other abnormalities or changes in your nail health? Share your experiences in a comment below, or start a conversation on your Activities page.