A few of my clients have developed a thin, ⅟4-inch-long brown line under a nail at one time or another. It starts in the middle of the nail and eventually grows out. The line appears whether they wear natural or artificial nails.
I can usually gently work out the line with a cotton-tipped orangewood stick when it grows a bit past the free edge. One of my clients suggested that it’s a hair that somehow works its way through the body and exits through the nail. I’m not worried about it, but I would like to know what it is.
The thin dark line could be cause by a number of conditions, none of which is cause for alarm. The symptoms you describe don’t indicate an infection or a tumor. I don’t believe the line represents the same disorder in all people. Some are undoubtedly splinter hemorrhages, which are tiny lines of clotted blood under the nail. Splinter hemorrhages, usually caused by injury to the nail, appear as ⅟4-inch-long, pencil-thin brown or black lines located near the middle of the nail.
A traumatized capillary in the nail bed cause blood to “pool” under the nail plate and bed, resulting in a splinter hemorrhage. The blood usually attaches to the underside of the nail plate and grows out with it. Because of the anatomical relationship between the nail plate and underlying nail bed, these small hemorrhages appear as longitudinal lines.
Lines in the nail plate can be caused by foreign bodies that have lodged under the nail plate. Depending on the client’s hobbies and occupation, it could be almost anything — dirt, hair, paint, or even a small piece of wire. If the object is tiny and the client is wearing nail polish at the time the object becomes lodged under her nail, the line won’t be visible until she removes the polish—making it appear to have developed suddenly. The object will eventually work itself out, or it might need a little prodding from the nail technician.
In response to your client’s hypothesis, a strand of hair cannot work itself out of the body through the nail. Hair is manufactured only by hair follicles, which are not found in the nail unit, and hair cannot be carried in the bloodstream. Even if a hair did somehow get into the bloodstream, it is impossible for the hair to work its way through the blood vessels and then exit the body via the nail. However, hairs frequently do become lodged under the nail. -Paul Kechijian, M.D.