Red or brown little streaks under the nails
Source: NHS
If you have littlered or brown streaks underneath your nails, it's likely they're splinter haemorrhages lines of blood caused by tiny damaged blood vessels.
A few splinters under one nail are nothing to worry about, and are most likely caused by aninjury of the nail. However, if many nails are affected, the splinters may be a sign of lupus erythematosus, psoriasis, an infection of the heart valves (endocarditis) or another underlying condition.