A small black line that forms vertically underneath your nail may be a splinter hemorrhage, while horizontal lines may be melanonychia. These may be harmless or a sign of a more serious health condition. As the name suggests, splinter hemorrhages look like a wood splinter under your nail.
The most common symptom of subungual melanoma is a discolored line that appears on your nail. It's usually brown or black and runs from top to bottom (vertical). In some cases, the line can be irregularly shaped and increase in length and width over time.
Nail hyperpigmentation is associated with vitamin B12 deficiency and its reversal on B12 supplementation is well reported in the literature.
It is most commonly seen in those with darker skin, although it can be found in lighter skinned individuals as well. While most of the time melanonychia is considered a normal finding, it could also be a sign of an underlying melanoma.
When to Contact a Medical Professional. Contact your provider if you notice splinter hemorrhages and you haven't had any recent injury to the nail. Splinter hemorrhages most often appear late in endocarditis. In most cases, other symptoms will cause you to visit your provider before splinter hemorrhages appear.
A black line on the nail could be normal, such as when it is just a color variation. Other possible causes range from injury or taking certain medications to various health conditions like human immunodeficiency virus (HIV) and melanoma.
Melanoma is more aggressive and can spread quickly. However, it can still go unnoticed for months or even years, particularly if it develops in less visible areas like the scalp, back, or under nails. Early-stage melanomas might look like ordinary moles, making them easy to overlook.
What deficiency causes black lines on nails? Deficiencies in vitamin B12, vitamin D, and protein can cause dark lines in nails. Other causes can include cancer, too much iron, and other health conditions.
Nail changes in vitamin B12 deficiency present as hyperpigmentation of nails like bluish discoloration of nails, blue-black pigmentation with dark longitudinal streaks, and longitudinal and reticulate darkened streaks. The nail pigmentation associated with B12 deficiency is more frequent in patients with dark skin.
Terry's nails is a type of nail discoloration. The nailbeds look “washed out,” except for a thin reddish-brown strip near the tip. Often, Terry's nails is a symptom of a chronic condition, such as liver failure or diabetes.
Emre Ali Demir
