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Black toenails

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Black toenails 

One of my favourite sayings to my runners is that you know you are a real runner when you lose a toenail.  Black toenails, also known as a subungual haematoma, are one of the risk factors when running long distances. They are created when you get a blood blister underneath the toenail. This article will explain nail anatomy, and discuss the causes treatment and prevention of black toenails


Black toenail anatomy

Anatomy of a Nail

Nails are made from Keratin, the same material as the skin and hair.  The nail plate is the hard part of the nail.  It grows from a line of cells underneath the skin at the base of the nail (Eponychium). Underneath the nail plate is the nail bed.  This is part of the nail that the blood blister forms.  The nail plate is no longer adhered to the nail bed once the black toenail has formed.  A pseudo nail may form under the black toenail.  In some cases the old nail falls off but with partial black toenails the damaged nail will grow out.   It takes about 6 months for a big toe nail to grow from the base so that is how long it might take for a black toenail to be replaced.

Causes of black toenails

For runners the main cause of black toenails is shoes that are too tight.  This can be from short shoes or more commonly shoes with a toebox that is too shallow for your toes.  However some runners have a dysfunction in the flexion of their big toe. They may preflex the toe to reduce the poor flexion.  This can result in them causing more trauma to their toe and they will wear a hole in the top of the toebox of the shoe.  Shoes that are too loose may also cause problems if your foot slips down to jam into the end of the shoe.  You may also claw your toes to try and keep the shoe on and this can cause black tonails in your smaller toes.  The risk of Black toenails increases the longer you go and the more downhill running you do.

Treating Black toenails

When you first get a black toenail it will often hurt.  This is caused by the trauma to the nail bed and the extra pressure from the fluid.  Severe pain can be relieved by draining the fluid in the nails.  I recommend you avoid draining the fluid for 24 hours after the black toenail has formed as there is a small risk of getting an infection in your blood (Septicaemia) while there is still a pathway through the blister.  You may prefer to come see me at the podiatry clinic to drain the fluid if it is causing problems.  Once the fluid in the blister is drained or reabsorbed the toenail should no longer hurt.  Having a partially attached toenail can cause further trauma to the toe so it may need to be removed where the nail is no longer attached.  If you have multiple black toenails on the same toe then the nail can get thicker and thicker.  This in turn increases the chance of damaging the nail again.  With repeated trauma the nail may permantely grow out thicker.

Preventing black toenails

It is not a pleasant experience for your performance in your major goal race to be affected by black toenails or blisters rather than fitness or tactics.  That is why it is important to do a few things to reduce the risk of getting black toenails

    1. Buy shoes that Fit.  Have some extra space at the end of your shoes if you are susceptible to black toenails.  This should be in the length and the depth of the toebox.  However it is equally important the the middle of the shoe fits firmly so you are not slipping around in the shoes.
    2. Keep your toenails short.  I cut my toenails short a few days before any long race.  I sometimes also thin the end of the nails down with a file.  Pressure on the nail moves it against the nail bed so short nails reduces the chance of a shearing force between the nailplate and nail bed.
    3. Fix damaged nails.  If you have a previous black toenail or damaged nails then it is a good idea to have them treated at the clinic before any major race.  I have some patients that see me every few months to make sure their nails are in good shape for their long races.

Steve Manning 

intraining Podiatrist  and Running Coach