What your nails can reveal about your health

As a medical student, I found nails to be one of the most challenging parts of my anatomy teaching. At first, I struggled to cope with the sight of painful injuries involving nails.

Perhaps that reaction came from seeing somebody rip a plaster from a stubbed big toe, only for the entire toenail to come away too. Ouch. I have since got over it, fortunately, because nails can reveal a great deal to doctors about a patient's health.

Like hair, fingernails and toenails are extensions of the skin. They consist of keratin, a durable substance that grows towards the fingertip to form a hard plate. The cuticle – the band of skin that covers the point where the skin and nail meet – provides further protection from injury and infection.

Pay attention to changes in your nails' texture or appearance, as they may offer valuable indications about your health. These are some of the main signs to watch for.

Spoon-shaped nails

Healthy fingernails and toenails should have a gentle convex curve, with no hollows or indentations. Koilonychia, by contrast, describes nails that are concave. In some cases, the central hollow is deep enough to hold a droplet of fluid, rather like medicine in a spoon – which explains the familiar term "spoon nails". Nails affected by this condition commonly appear thinner and may also become more fragile.

Koilonychia may be a sign of anaemia, in which too few red blood cells are circulating to transport oxygen to the body's tissues. It is linked to iron deficiency. Poor diet, coeliac disease and cancer of the gastrointestinal tract are among the possible causes of low iron.

Mechanics and hairdressers may face a particular risk of koilonychia because they work with petroleum-based solvents, including those in engine oil and perm products. Yet spoon-shaped nails have a wide range of potential underlying causes, so it is sensible to speak to your GP if the condition persists for a prolonged period.

Discoloured nails

Under normal circumstances, nail beds – the skin below the nail – should be a well-perfused pink colour. Illness or infection can alter the colour of the nail bed or the entire nail. Yellow nails, for example, may point to a fungal infection or to changes caused by a skin condition such as psoriasis.

Leukonychia is the medical name for white nail discolouration, and it can appear in several different forms.

In certain instances, white marks on nails may signal poisoning from heavy metals such as lead or arsenic. Both substances continue to cause problems in many parts of the world because of pollution in water supplies.

When whiteness covers the whole nail and affects several nails, a lack of protein in the bloodstream is a more likely explanation. This can potentially be an indication of liver disease or kidney disease.

Small white spots on a nail, however, are most likely to result from traumatic injury. This could range from stubbing a toe or dropping a heavy item on it, to trapping a finger in a door. Nail biting and excessively vigorous manicures can also damage nails.

Anyone who has stubbed a toe or caught a finger may also have seen the nail turn dark purple, blue or red. This is known as a subungual haematoma: blood collects between the nail and the nail bed following an injury. These usually resolve naturally with time, although they can cause infection or make the nail separate from its bed.

Emergency nail tests

In a medical emergency, doctors frequently examine a patient's nails to assess blood oxygen saturation. They use a pulse oximeter, which clips onto a finger, passes light through the fingertip and measures the blood flowing through it. This shows how much oxygen is getting into the blood, and consequently how efficiently the heart and lungs are functioning.

The capillary refill time (CRT) test provides another measure of how effectively circulation is working. A clinician presses a nail or fingertip for five seconds, causing the skin below to blanch.

Once the pressure is released, the skin should regain its former colour within two seconds. If it takes longer, you may be cold or dehydrated, or have poor peripheral perfusion. This means either that the heart is not pumping strongly enough or that something is preventing sufficient blood from reaching the most distant areas of the body, potentially because of shock.

Pressing on nails can also be used when assessing a patient who is unconscious or drowsy. This forms part of the Glasgow Coma Scale, which evaluates responsiveness and the degree of impaired consciousness in patients.

When to seek advice about unusual nails

There are numerous nail problems beyond those described here, including nails that crumble, have pits or lines, appear clubbed or swollen, or show red markings beneath them. The possible diagnoses are equally broad, spanning minor conditions through to serious illnesses.

If you are concerned about nail discolouration or an altered nail shape, arrange for your GP to examine them. The same applies to severe nail injuries, particularly if the nail has been pulled off. When the skin beneath a nail is injured, proper care is essential to avoid complications such as infection, and to check for additional damage, including a broken bone.

One final caution: artificial or painted nails may conceal visible changes. Try not to gloss over your nails, and pay attention to what they could be telling you about your health.

Dan Baumgardt, Senior Lecturer, School of Physiology, Pharmacology and Neuroscience, University of Bristol

This article is republished from The Conversation under a Creative Commons licence. Read the original article.