What can cause thickened nails?
Thickened nails are common and have many different causes. The most common are listed below.
Fungal nail
Fungal nails are extremely common; a large proportion of adults have a fungal infection of at least one toenail. When the infection is long-standing (and the fungal threads have multiplied extensively), the nail plate thickens. Fungal nails can strongly resemble onychauxis, a thickening of the nail often seen in older people that does not necessarily involve a fungal infection.
Psoriatic nail
Psoriasis is a common skin condition that also often affects the nails. The changes can consist of small pits, lengthwise lines in the nail, and thickening of the nail plate. Often there is also thickening under the nail plate, so the end of the nail is lifted slightly. Like a thickened nail, a psoriatic nail is also often infected with a fungus, and treating the fungus will then not restore the nail plate.
Onychauxis
In onychauxis there is a thickening of the nail plate without an underlying problem. These nails, often difficult to cut, are very commonly seen in older age. It can be hard to distinguish this normal, age-related thickening from a fungal nail, and not rarely such a thickened toenail is also affected by fungus and contains fungal spores.
Onychogryphosis (ram’s horn nail)
In onychogryphosis there is a strong thickening and curving of the nail plate. The cause is not entirely clear; sometimes damage to the nail bed seems responsible, but a fungal infection could also trigger it.
Other nail problems
Various skin diseases can be accompanied by nail changes such as thickening of the nail plate, for example lichen planus, alopecia areata and pityriasis rubra pilaris.
When to see a doctor
See a doctor if a nail becomes thickened, discoloured, crumbly or difficult to cut, or if it bothers you, so the cause can be found and any fungus or skin condition treated.