If you mean the viral claim “lines on your nails mean you have cancer,” that’s not generally true.
- Vertical ridges/lines (running from cuticle to tip) are very common and are usually harmless.
- Horizontal grooves across the nail, called Beau’s lines, can happen when nail growth is temporarily interrupted—for example by fever, injury, major stress, or chemotherapy.
- A new brown or black streak running lengthwise under one nail is different. It can sometimes be a sign of nail melanoma, although many non-cancerous conditions can also cause dark streaks. A changing dark streak should be checked by a dermatologist.
So, ordinary nail lines do not mean you have cancer.
If you tell me whether your lines are vertical or horizontal, and what color they are, I can explain what they most likely mean
