Other causes include certain medications, fungal infections, and increased pigment production in the nail. A condition called longitudinal melanonychia produces a brown or black band running lengthwise along the nail. Some bands are benign, but others may need examination to rule out nail-unit melanoma, a rare form of skin cancer that develops in or around the nail apparatus.
Warning features include a new or widening dark band, irregular borders, multiple shades of color, pigment spreading onto the surrounding skin, or a mark that changes over time. A dark mark that appears without a clear injury is particularly worth checking.
It is not possible to distinguish every harmless mark from melanoma by looking at a photograph. If you notice a new, unexplained dark streak or a changing pigmented area, arrange an appointment with a dermatologist or another qualified healthcare professional as soon as practical. Do not wait for the mark to disappear on its own.
Black discoloration can also follow trauma or infection, so it does not automatically mean cancer. The purpose of an examination is to identify the cause rather than assume the worst.
Red nails and other unusual color changes
Red discoloration can also have several explanations. Sometimes, a red or reddish-brown area is caused by minor injury, pressure, or inflammation around the nail. Other patterns may occur alongside skin conditions such as psoriasis or autoimmune diseases such as lupus.
Certain nail findings can also be associated with heart or kidney conditions, but these relationships are complex. A red-looking nail does not automatically mean that an organ is damaged, and different patterns of discoloration can have very different causes.
For example, tiny red-brown lines beneath the nail may sometimes develop after small blood vessels are injured. Similar-looking marks can occur in different medical situations, so the appearance alone is not enough to identify the cause.
If the nail color changes persist, affect several nails, or appear together with fatigue, fever, joint pain, swelling, breathing problems, or other new symptoms, discuss them with a healthcare professional. An examination can help determine whether the change is local to the nail or part of a broader health issue.
2. Nail Texture and Shape: Signs Beyond Color
Color is only one part of nail health. The surface, thickness, shape, and rate of growth can also change. These features often reflect everyday wear or local nail problems, but persistent changes sometimes provide useful clues for a medical assessment.
Brittle nails that split or break easily
Brittle nails are a common complaint. They may peel into layers, crack at the edges, or break with little pressure. Repeated exposure to water, frequent handwashing, cleaning products, nail polish remover, and harsh manicures can weaken the nail plate.
Brittleness can also occur with aging, certain skin conditions, thyroid disorders, or nutritional deficiencies. Iron deficiency is one possible contributor, especially when nail changes occur alongside symptoms such as tiredness, weakness, or unusual pallor.
The best approach is to consider the overall pattern. If your nails become brittle after frequent cleaning or cosmetic treatments, reducing exposure to irritants and moisturizing the hands may help. Wear protective gloves for prolonged wet work and avoid repeatedly using harsh nail products.
If brittleness develops suddenly, affects many nails, or persists despite gentle care, a medical assessment may be appropriate. A clinician can decide whether tests for iron deficiency, thyroid problems, or another cause are necessary.
Thickened, crumbly, or lifting nails
Nails that become unusually thick, yellow, crumbly, or separated from the underlying nail bed may have a fungal infection. Trauma, psoriasis, and other nail disorders can produce similar changes.