Curved Toenail Pain: Involuted & Pincer Nails Explained
31 August 2026
By Mark Reyneker, BTech (Podiatry), MSc (Palaeontology), Registered Podiatrist, Foot & Gait Specialist | Founder & Clinical Director, Family Podiatry Centre
Published: 31 August 2026 | Last reviewed: 31 August 2026
Why some toenails become excessively curved, why the sides become painful, and what can be done about it
Why some toenails become excessively curved, why the sides become painful, and what can be done about it
An involuted toenail is a nail that has become excessively curved from side to side. Instead of growing relatively flat across the top of the toe, the sides of the nail turn downward towards the nail grooves.
At first, this may simply look like an unusually curved nail. But as the curvature increases, the edges of the nail can place considerable pressure on the soft tissue running along either side of the nail.
That pressure can hurt.
It can also make shoes uncomfortable, cause recurrent hard skin or corns within the nail grooves and, in some cases, eventually contribute to an ingrown toenail.
This distinction is important because an involuted nail and an ingrown toenail are not quite the same problem.
With an ingrown toenail, the edge or a sharp portion of the nail penetrates or traumatises the surrounding nail fold, producing inflammation and sometimes infection.
With an involuted nail, the problem may begin much earlier:
the nail itself is simply too curved for the space underneath it.
Understanding that difference changes how we think about treatment.
What is an involuted toenail?
Look at a healthy big toenail from the end of the toe.
The nail normally has some transverse curvature. It is not supposed to be completely flat.
In an involuted nail, however, this transverse curve becomes exaggerated.
The sides of the nail progressively turn downwards.
In more pronounced cases, the nail can take on an inverted U-shape, C-shape, omega shape or even an almost tubular appearance. The severe end of this spectrum is commonly described in the medical literature as pincer nail deformity.
Pincer nail has been defined as excessive transverse curvature of the nail plate that can compress the nail bed and surrounding soft tissues.
Researchers have even developed objective methods of measuring this deformity. One is the curvature index, which compares the actual curved length of the nail with the apparent width of the nail when viewed from the end of the toe.
The greater the difference, the more curved the nail.
This is useful because it demonstrates something patients often already recognise intuitively:
the problem is not necessarily that the nail is too wide. It is that the nail is too curved.
Why does an involuted nail hurt?
The anatomy explains the symptoms remarkably well.
The toenail is a relatively rigid keratin plate sitting over the nail bed. On either side are the lateral nail folds and nail grooves.
When the nail becomes excessively curved, its lateral edges rotate downwards.
These edges can then exert concentrated pressure against the tissue within the nail grooves.
Imagine taking a relatively flat strip of material and progressively bending its two edges downward.
As the curvature increases, the edges become more vertically orientated and the available space beneath the nail becomes narrower.
The soft tissue is effectively being compressed between the curved nail plate and the underlying structures of the toe.
This is why an involuted nail may hurt even when:
- there is no obvious infection;
- there is no pus;
- there is no granulation tissue;
- and the nail has not obviously pierced the skin.
The pain can be predominantly mechanical pressure pain.
Shoes can make this considerably worse.
A shoe that compresses the toes from the sides or presses down over the nail increases the force acting on an already sensitive nail groove.
The result is often the familiar complaint:
“It hurts down the sides of my nail, especially in shoes.”
Involuted nail vs ingrown toenail
These terms are frequently used interchangeably, but they describe different aspects of nail pathology.
Involuted nail
The principal abnormality is excessive curvature of the nail plate.
The curved sides press into the nail grooves.
Ingrown toenail
The principal problem is interaction between the nail edge and the surrounding nail fold, usually producing tissue injury, inflammation and sometimes secondary infection.
Pincer nail
This describes a pronounced transverse overcurvature of the nail and is generally considered the more severe morphological expression of an involuted nail.
Importantly, these conditions can overlap.
An excessively curved nail may eventually produce enough pressure or trauma to behave like an ingrown toenail.
This is one reason patients with involuted nails may experience repeated episodes of “ingrown toenails” even after repeatedly cutting away the painful corner.
The corner may not be the fundamental problem.
Why do toenails become so curved?
This is where the biology becomes particularly interesting.
There is probably no single explanation for every involuted or pincer nail.
Reported associations include genetic predisposition, repeated trauma, changes in the nail bed, fungal nail disease, abnormalities around the distal phalanx and altered mechanical forces acting on the toe.
Some people appear to have naturally more curved nails.
Hereditary pincer nail deformities have been reported across multiple generations, supporting a genetic component in at least some patients.
Acquired cases, however, can develop later in life.
The relationship between the nail, nail bed and underlying bone is particularly important.
The nail is not simply growing on top of the toe
It is tempting to imagine the toenail as a passive sheet of keratin that grows forwards.
The reality is more complicated.
The nail plate, nail matrix, nail bed, surrounding soft tissues and distal phalanx form a mechanical system.
Changes within one component may therefore influence the others.
Several theories have been proposed to explain pincer nail formation.
One early theory suggested that changes in the shape of the distal phalanx or the development of an underlying osteophyte could mechanically alter nail curvature.
However, subsequent morphological research complicated this explanation.
Kosaka and colleagues compared normal, ingrown and pincer nails and suggested that the excessive curvature may be related to contraction or narrowing of the nail bed itself. Their findings also raised the possibility that some underlying bony changes may be a consequence rather than the original cause of the deformity.
The precise mechanism therefore remains incompletely understood.
That uncertainty is important.
It would be misleading to tell every patient with an involuted nail that the condition has one simple cause.
Could the way we load our toes influence nail shape?
This is one of the most interesting areas of pincer-nail research.
Toenails are exposed to mechanical forces every time we stand and walk.
When the toe contacts the ground, the plantar soft tissues experience upward force while the nail plate provides resistance above.
Researchers have proposed that this mechanical interaction may help maintain normal nail shape.
A small case-control study by Sano, Shionoya and Ogawa compared people with bilateral pincer nails with matched controls.
The findings were striking.
People with pincer nails demonstrated significantly lower pressure beneath the first toe during walking, both barefoot and in shoes.
In the control group, the hallux frequently represented the area of peak plantar pressure.
In the pincer-nail group, loading was shifted more towards the metatarsal region.
This led the authors to propose that insufficient mechanical stimulation beneath the toe may contribute to excessive nail curvature.
This is an intriguing hypothesis rather than definitive proof.
The study was small, involving 12 people with bilateral pincer nails and 12 controls, so it cannot establish that reduced hallux loading causes involuted nails.
Nevertheless, it raises an important biomechanical possibility:
nail shape may partly reflect how the toe is being used.
For podiatrists, this is particularly interesting because it connects nail pathology with gait and foot function rather than treating the toenail as an isolated structure.
Shoes can affect the problem in more than one way
Shoes are frequently blamed for painful toenails, but the relationship is more complicated than simply saying that “tight shoes cause involuted nails”.
A narrow toe box can certainly compress the nail folds against an already curved nail.
A shallow shoe can also apply pressure from above.
Both can increase symptoms.
But footwear could potentially influence nail mechanics in another way.
In the Sano study, participants with pincer nails demonstrated even lower hallux pressure while wearing shoes than while barefoot.
This does not prove that shoes caused their nail deformity, but it supports the idea that footwear can modify the mechanical environment of the hallux.
For somebody with a painful involuted nail, footwear assessment therefore makes sense for two reasons:
- reducing direct compression around the nail, and
- considering how the shoe affects loading of the big toe during walking.
Why cutting down the sides can make matters worse
This is one of the most common cycles we see clinically.
The side hurts.
So the person cuts the corner away.
There is temporary relief because the offending piece of nail is no longer pressing against the skin.
But the nail continues growing.
Eventually the shortened edge reaches the nail groove again.
It may now have a sharp corner or nail spicule.
The patient cuts it again.
Over time, the nail becomes progressively narrower while the underlying curvature has not necessarily changed.
The result can become a repeating cycle:
pressure → pain → cut the corner → temporary relief → nail regrowth → pressure again.
If a sharp nail spicule is left behind, the problem can progress into true onychocryptosis.
This is why repeatedly “digging out” the sides of an involuted nail is not always a good long-term solution.
Hard skin can develop down the side of the nail
Another frequently overlooked consequence is onychophosis.
Onychophosis is the accumulation of hyperkeratotic tissue—essentially a small corn or area of hardened skin—within the nail groove.
This makes mechanical sense.
Skin responds to repeated pressure and friction by producing additional keratin.
If an involuted nail continuously presses against the nail groove, the skin can gradually become thickened.
Now there are two structures competing for the same limited space:
the curved nail edge and the hardened skin.
Pressure increases further.
Patients sometimes assume the nail itself is cutting them when a considerable component of their pain is actually coming from this compacted hyperkeratotic tissue.
Removing the hard skin can therefore provide substantial relief, although recurrence is possible if the underlying nail pressure remains.
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Can fungal infection cause an involuted nail?
Fungal nail infection—onychomycosis—can alter nail thickness, texture and shape and has been associated with pincer nail deformity.
However, not every thick or curved nail is fungal.
This distinction matters because antifungal medication will not straighten a mechanically or structurally involuted nail if fungus is not responsible for the deformity.
Where fungal infection is suspected, appropriate examination and, when necessary, laboratory confirmation can help establish whether onychomycosis is actually present.
How should an involuted toenail be assessed?
Treatment should start by identifying what is actually causing the pain.
A clinical assessment may consider:
Nail curvature
How severely is the nail curved?
Location of pain
Is pressure occurring on one side or both sides?
Skin condition
Is there inflammation, infection, granulation tissue or onychophosis?
Nail thickness
A thick nail occupies more space and can increase shoe pressure.
Nail integrity
Is there a sharp spicule or fractured edge?
Possible fungal infection
Is the nail thickened, discoloured or friable?
Footwear
Is the toe box compressing the nail?
Toe and foot mechanics
Where clinically appropriate, gait and plantar loading may also be considered, particularly when there appears to be abnormal hallux function.
Not every patient requires every investigation.
The objective is to determine whether we are dealing primarily with a curvature problem, an ingrown nail, a skin problem, an infection—or a combination of these.
Treatment: the least invasive effective option
Treatment should be proportional to the severity of the problem.
A mildly curved nail that occasionally becomes uncomfortable does not automatically require nail surgery.
Conversely, repeatedly treating a severely involuted nail symptomatically without addressing the underlying curvature may result in recurrent pain.
A useful approach is therefore to progress from conservative management towards more definitive procedures when necessary.
This is broadly consistent with modern management principles and the recent German S1 guidance addressing ingrown and pincer nails.
1. Reduce pressure around the nail
For relatively mild cases, reducing mechanical irritation may be enough to settle symptoms.
This can include:
- wider footwear;
- sufficient depth over the toes;
- avoiding shoes that squeeze the big toe against the second toe;
- avoiding repeated aggressive cutting into the nail grooves;
- and appropriate professional reduction of painful nail or callused tissue.
These interventions do not necessarily change the fundamental curvature of the nail, but they can substantially reduce the forces responsible for symptoms.
2. Reduce nail thickness where appropriate
Some involuted nails are also unusually thick.
Careful reduction of nail thickness can reduce bulk and pressure and may also influence the mechanical stiffness of the nail plate.
Nail grinding has been investigated as a conservative treatment for pincer nails, with studies reporting improvements in nail morphology.
This should be performed appropriately because excessive reduction can damage or weaken the nail.
3. Clear painful nail grooves
Where compacted skin or onychophosis has developed, carefully removing the hyperkeratotic material can create more room around the nail edge.
This can sometimes produce surprisingly rapid pain relief.
But again, this addresses the consequence of pressure, not necessarily the reason the nail is curved.
If the curvature remains pronounced, the hard skin may gradually return.
4. Nail bracing: changing the curvature rather than simply cutting the nail
For a persistently involuted nail, one of the most interesting conservative treatments is orthonyxia, commonly known as nail bracing.
The principle is similar to orthodontics.
Instead of repeatedly cutting away the curved sides, a brace applies controlled corrective force to the nail plate.
The objective is gradually to reduce excessive transverse curvature.
Different systems have been developed, including metal wire braces, plastic braces, resin systems and shape-memory devices.
Evidence remains less extensive than we would ideally like, but clinical studies have demonstrated improvement in nail curvature and symptoms with several bracing techniques.
A randomised clinical trial examining a polyethylene nail brace for onychocryptosis found that combining treatment of the offending nail edge with bracing reduced recurrence compared with treatment of the nail edge alone.
Other studies of conservative splinting have reported pain reduction and progressive improvement in nail shape.
The attraction of orthonyxia is straightforward:
it attempts to modify the mechanical deformity while preserving the nail.
Treatment is not instantaneous, because toenails grow slowly and the nail needs time to remodel.
For an appropriately selected patient, however, this can be preferable to repeatedly cutting the sides away.
5. When does an involuted nail require surgery?
Some nails are simply too severely deformed, painful or recurrent for conservative treatment to provide an acceptable long-term result.
Surgery may be considered when there is:
- severe curvature;
- persistent pain despite conservative treatment;
- repeated ingrowing or inflammation;
- recurrent nail spicules;
- significant soft-tissue compression;
- failure of bracing or inability to use a brace;
- or substantial interference with footwear, walking or daily activities.
The exact procedure depends on the pathology.
This is another reason why distinguishing an involuted nail from an ingrown toenail matters.
Partial nail surgery
When one or both nail edges repeatedly produce painful onychocryptosis, the problematic section of nail can be removed.
A matricectomy may then be performed to prevent that portion of the nail from growing again.
Chemical agents such as phenol have traditionally been widely used, while surgical, electrosurgical, radiofrequency and other matrix-ablation techniques are also available.
A 2023 systematic review of randomised trials found that adding phenol to nail avulsion appeared to reduce recurrence compared with avulsion alone, although the authors emphasised that the overall quality of evidence was low.
A newer 2026 network meta-analysis involving 44 studies and more than 5,000 participants similarly found that simple nail avulsion carried the greatest recurrence risk. It also suggested that differences between several contemporary matricectomy and surgical techniques may be smaller than traditionally assumed.
The important principle is therefore not simply:
“remove the nail.”
It is to identify the structure responsible for recurrence and choose a procedure capable of addressing it.
What about removing the entire toenail?
Complete nail removal is rarely the first answer to an involuted nail.
If the nail matrix remains intact, the nail can simply grow back with the same underlying tendency.
There are also cosmetic and functional consequences to permanently removing an entire nail.
For most patients, preserving as much healthy nail as possible is preferable.
More extensive procedures are generally reserved for severe deformities or situations where less invasive treatment has failed.
Can an involuted toenail be permanently fixed?
Sometimes.
But “permanent” depends on what is causing the deformity and which treatment is used.
Removing painful hard skin may provide excellent relief but does not permanently alter nail shape.
Thinning the nail may reduce pressure but requires maintenance.
Changing footwear may remove an aggravating factor without altering an established deformity.
Nail bracing attempts to remodel the curvature while retaining the nail, although recurrence can occur.
A partial matricectomy can permanently prevent a problematic portion of the nail from regrowing, but this permanently makes the nail narrower.
More extensive reconstructive procedures can alter the anatomy of severe pincer nails but are correspondingly more invasive.
There is therefore no single “best” procedure for every involuted toenail.
The correct treatment depends on how curved the nail is, why it hurts and whether the objective is symptom control, correction of curvature or prevention of recurrence.
When should you see a podiatrist?
Professional assessment is particularly useful when:
- the sides of the nail repeatedly hurt;
- you have to keep cutting down the corners;
- the nail appears increasingly curved;
- hard skin repeatedly develops in the nail grooves;
- shoes cause significant nail pain;
- the skin becomes red, swollen or produces discharge;
- the problem keeps returning;
- or you are unsure whether you have an involuted nail, ingrown toenail or fungal nail infection.
People with diabetes, impaired circulation, neuropathy or impaired healing should be particularly cautious about attempting to dig underneath or cut deeply down the sides of a painful toenail themselves.
The important point: look at the shape of the nail
A painful toenail is often treated as though the only question is whether it is “ingrown”.
That can miss an important part of the problem.
Look at the nail from the front.
If the nail is markedly curved and both sides are turning downward into the nail grooves, the nail's geometry itself may be contributing to the pain.
That changes the clinical question.
Instead of asking only:
“How do we remove the painful corner?”
we should also ask:
“Why is so much pressure developing along the sides of this nail?”
Sometimes the answer is inflammation.
Sometimes it is a nail spicule.
Sometimes it is hard skin.
Sometimes it is footwear.
And sometimes the nail is simply too curved.
Recognising that difference allows treatment to target the underlying mechanical problem rather than repeatedly treating its consequences.
Key points
- An involuted toenail has excessive transverse curvature, causing the sides of the nail to turn downwards.
- A pincer nail represents a more pronounced form of transverse nail overcurvature.
- An involuted nail can be painful without actually penetrating the skin.
- The pain may result from mechanical compression of the lateral nail grooves.
- Involuted nails and ingrown toenails can occur together, but they are not synonymous.
- Repeatedly cutting down the sides may provide temporary relief without correcting the underlying curvature.
- Hard skin called onychophosis may develop in the nail groove and further increase pressure.
- Treatment can range from footwear modification and professional nail care to nail bracing and, when necessary, nail surgery.
- Nail bracing is particularly interesting because it attempts to change nail curvature while preserving the nail.
- Severe or recurrent cases require assessment of the nail shape, surrounding tissue and underlying cause rather than simply repeated removal of the painful corner.
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Disclaimer: The word "treatment" in this article refers to the care and management of a patient’s health to prevent, cure, or improve a condition. Treatment results vary and do not necessarily indicate a cure. This article is for informational and educational purposes only and does not constitute medical advice.
About the Author
Mark B. Reyneker, BTech (Podiatry), MSc (Palaeontology) is a podiatrist and Founder & Clinical Director of Family Podiatry Centre, with more than 25 years of clinical experience across South Africa, Malaysia and Singapore. His clinical interests include foot and lower-limb pain, gait and biomechanics, sports-related foot conditions, orthotic therapy and footwear.
Alongside his clinical practice, Mark conducts research into human gait and foot biomechanics. His MSc research at the University of the Witwatersrand investigated human propulsion and the structural properties of the metatarsals. He is also the inventor of A Foot Orthotic, an orthotic technology developed through an international patent family.
Frequently Asked Questions
- What is the difference between an involuted toenail and an ingrown toenail? An involuted toenail is excessively curved downward on the sides, creating mechanical pressure in the nail grooves. An ingrown toenail occurs when a sharp edge of the nail actually pierces the surrounding skin, typically causing inflammation or infection.
- What is a pincer nail deformity? A pincer nail is the most severe form of an involuted nail. The transverse curvature becomes so extreme that the nail resembles an inverted U-shape, C-shape, or tube, physically pinching the underlying nail bed.
- Why does my curved toenail hurt if it isn’t infected? As the nail curves inward, its rigid edges compress the soft tissue in the nail grooves against the underlying structures of the toe. This creates concentrated, localized pressure pain, even if the skin is perfectly intact.
- Can wearing tight shoes cause involuted toenails? While shoes may not be the root cause of the curvature, footwear that squeezes the toes from the sides or presses down on the nail drastically increases the mechanical force acting on the nail grooves, triggering or worsening the pain.
- Are naturally curved toenails hereditary? Yes, genetics can play a role. Hereditary pincer nail deformities have been documented across multiple generations, meaning some individuals naturally inherit a predisposition to excessively curved nails.
- Can a fungal infection make my toenail curl inward? Yes. Fungal nail disease can alter the structure, thickness, and health of the keratin plate, which is a known contributing factor to the development of acquired involuted nails.
- Does the way I walk affect the shape of my toenails? Research suggests it might. Studies indicate that individuals with pincer nails often exert significantly lower pressure beneath their big toe during walking, leading researchers to propose that insufficient mechanical stimulation beneath the toe may contribute to excessive curvature.
- Should I cut the painful corners out of my curved toenail? Repeatedly digging out or cutting away the painful corners usually only provides temporary relief. It can actually increase the risk of turning an involuted nail into a true ingrown toenail as the cut edge grows back into the skin.
- Can an involuted toenail turn into an ingrown toenail? Yes. If the excessive curvature continues to apply pressure or cause micro-trauma to the nail fold over time, the nail can eventually pierce the skin and behave exactly like an ingrown toenail.
- How do podiatrists fix a toenail that curves inward? Treatment depends on the severity. It can range from conservative management—such as proper straight-edge nail trimming, footwear modifications, and mechanical offloading—to advanced podiatry techniques like nail bracing or minor surgical procedures to permanently remove the curving borders.
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