Brown streaks beneath a thumb nail can result from splinter hemorrhages. The lines of blood underneath the nails come from damaged minuscule blood vessels in the thumb. A less serious cause is a simple injury of the nail, according to the National Health Service.Continue Reading
When melanoma is the cause of brown streaks under the nail, the pattern involves multiple streaks running along the underside of the nail vertically from the tip of the nail to the quick. It also generally appears on just one nail, but if the cause of the stripes is related to dark skin, the stripes are likely to appear on multiple nails, explains the National Health Service.
Splinter hemorrhages are thinner than the stripes that indicate melanoma. Sometimes these hemorrhages occur when trauma occurs to the nail, such as when a person slams a door on a nail or drops a heavy object on it. At other times, these hemorrhages are a sign of serious conditions, such as lupus erythematosus or endocarditis, an infection of the valves of the heart. If several nails show these thin stripes, and no physical trauma has affected the nails recently, seeking medical attention is advised, notes the National Health Service.Learn more about Skin Conditions