What causes these HORIZONTAL ridges in my fingernails?

Dermatologists are the doctors for skin, but also for hair and nails.  Most of the time patients ask questions about their nails as an afterthought at their visit.  Questions about ridges in fingernails are very common.

Generally, there are two main types of ridges in the nails – horizontal and vertical.  We’ll talk about horizontal ridges today called Beau’s lines.  Stay tuned for vertical ridges.

First let’s review the anatomy of the nail.  The nail is surrounded on three sides by what is called the nail fold.  Two lateral nail folds on each side, and the proximal nail fold is at the base of the nail by the cuticle.  The hard part of the nail is called the nail plate.  The nail plate is synthesized by the nail matrix which sits under the cuticle and proximal nail fold.  Horizontal grooves in the nail plate generally occur due to halting of the growth of the nail. This can occur for a few reasons.

Onychomadesis is the fancy name for halting of nail growth.  This usually occurs due to severe illness or nutritional deficiency.  Usually, you will see this in all the nails, not just one.  The horizontal groove is at about the same place in each nail and slowly grows out at the same rate.  The depth of the groove is determined by how long the growth was halted.  A very deep groove and halting can lead to developing a totally new and separate set of nails.  The most severe example of this I can remember is when my kids had hand foot and mouth as toddlers.  They lost all their toenails!

Rash at the proximal nail fold.  A recurrent flare of rash, most commonly psoriasis, can lead to a series of horizontal grooves in the nail as well as something called nail pits. For this reason, it is important to keep rash under control around the nails.

Trauma to the proximal nail fold.  On fingers, this usually occurs by habitually rubbing the nail plate.  This usually causes a wavy look with horizontal ridges in its mildest form, and much more severe and permanent deformity with prolonged habitual rubbing.  

Trauma to the toenail proximal fold is most commonly seen in athletes and hikers.  When the foot and nail repeatedly strikes the inside of the toe box, it can traumatize the proximal nail fold so much that a ridge forms later, or there is onychomadesis to the point of nail loss. I personally have lost some toenails each time I have run a marathon.  This is usually only seen in one or a few toenails and often can be associated with bruising at the proximal nail fold. 

Final thought about horizontal grooves.  Generally it takes 6 months for the fingernails to grow from bottom to top and 12 months for toenails to grow bottom to top.  With horizontal grooves you can watch them grow out and estimate how long ago they occurred.  For instance, a horizontal groove halfway up the fingernail usually occurred from damage 3 months prior.  

Because it takes so long for the nail to grow out, it is important to protect that proximal nail fold, because you’re gonna be waiting a LONG time for the nail to look normal again.

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