A fungal nail infection is the same family of organisms that causes athlete's foot, established in the keratin of the nail rather than the skin. The nail thickens, discolours and separates from its bed, and because a nail grows slowly, improvement is measured in the growth of new nail rather than in the appearance of the old.
What is actually happening in the skin?
A nail is not living tissue. It is a plate of compacted keratin produced by cells at its base, pushed forward continuously, and it is chemically much the same material as the outermost layer of the skin. Anything that can digest keratin can therefore live there, and fungal organisms do exactly that.
That is what happens here. Fungal organisms that digest keratin establish themselves in the plate, usually entering at the free edge or along the sides, and work inwards. Debris accumulates underneath, which lifts the nail from its bed and produces the thickening and the change of colour.
Nothing about this is an infection of living tissue in the ordinary sense, and that explains the timescale. The immune system reaches keratin poorly and the plate cannot heal, so the damaged nail does not recover; it has to grow out and be replaced. Toenails grow slowly enough that the process is measured in seasons.
The route in for a fungal infection is usually the skin. An infection between the toes that has been present for a long time is the classic origin, which is why a clinician examining a nail will look carefully at the foot around it. Warmth, moisture and enclosed footwear all favour the fungal organisms rather than the person.
How would a dermatologist describe it?
Onychomycosis is the clinical word, combining the terms for nail and fungus. It appears in letters and reports where everyday speech would say a fungal nail.
Onycholysis describes the separation of the plate from the bed beneath it, and it is the change responsible for the white or yellow area that spreads back from the edge. Clinicians name it separately because several conditions cause it.
Subungual hyperkeratosis describes the debris accumulating under the nail. Dystrophy is the general term for a nail that has lost its normal structure, and it carries no implication about cause.
Which part of the nail is affected gets described specifically, because the pattern of entry differs between organisms and between conditions. That description is also why a clinician looks at every nail rather than the one you point at.
What usually happens at a consultation?
The history covers how long the nail has looked like this, whether the skin of the foot is or has been affected, what has already been tried and for how long, and whether anyone in your family has psoriasis. That last question matters more than it sounds.
The examination covers all the nails, fingers included, and the surrounding skin. Changes of this kind have several causes, and the pattern across several nails is far more informative than the appearance of one.
A sample is usually taken before anything is decided, by clipping the nail and sometimes scraping debris from beneath it. The procedure is quick and painless, and it is described in its own page on this site. Results take a while, and being told that in advance prevents an anxious wait.
Expect a conversation about timescales that may be longer than you hoped. A nail that has been abnormal for years will not look different for many months whatever is decided, and setting that expectation is part of the appointment.
What is worth asking?
Ask what the clinician thinks is causing the change, and how confident they are that it is fungal before the sample returns. Psoriasis and injury both produce nail changes that resemble infection closely.
Ask how progress will be judged. The answer should be about new growth at the base rather than the appearance of the existing plate, and knowing that in advance prevents an entirely normal recovery reading as failure.
Ask whether the skin of the foot needs attention alongside the nail. Leaving a fungal reservoir on the skin is a recognised route back, and it is easy to overlook when the nail is the visible problem.
Before the appointment, remove any varnish and take a photograph in daylight. Both make the assessment easier, and neither occurs to most people until they are asked in the room.
What this page does not do
Nothing here tells you whether a nail change is fungal. Psoriasis, injury and several other conditions produce a thickened discoloured nail, which is precisely why a sample is taken. No treatment is recommended, no medicine named, and no course, strength or duration appears anywhere on this page.
Common questions
Why does it take so long to improve?
Because a nail cannot be repaired, only replaced. The damaged part grows out from the base and the visible improvement tracks that growth, which is slow in fingernails and slower still in toenails. Judging progress by the old nail rather than by the new one is the most common reason people conclude nothing is working.
Is it connected to athlete's foot?
Frequently. The same organisms cause both, and an untreated infection between the toes is a recognised route to the nails. That is why a clinician looking at a nail will also look at the skin around it.
Why is a sample taken before anything is done?
Because several conditions thicken and discolour a nail without any fungus involved, and psoriasis is the most common of them. Establishing what is present avoids a long course aimed at the wrong thing.
Does nail varnish matter?
It can obscure the nail and it may interfere with taking a usable sample, so clinics usually ask for it to be removed beforehand. Checking that when the appointment is made saves a wasted visit.
Can it come back?
Recurrence is recognised, particularly where the skin of the foot remains affected or where footwear keeps the area warm and damp. A clinician can tell you which of those apply in your case.
Sources
- Fungal nail infection — NHS (United Kingdom) · accessed
- Patient information on skin conditions — British Association of Dermatologists (United Kingdom) · accessed
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