Psoriasis is an autoimmune disease that causes plaques and lesions on the skin. When symptoms develop on toenails and fingernails, they can resemble nail fungus. However, fungal infections are contagious, and psoriasis is not.

The autoimmune activity in psoriasis causes the rapid overgrowth of skin cells. These cells build up in the skin, contributing to the characteristic lesions of condition.

Nail fungus is a type of infection. People often pick up fungal nail infections in moist locations, such as pool decks and locker rooms. However, the fungus can have many other sources.

Knowing the difference between nail psoriasis and nail fungus can prevent symptoms from becoming worse or the infection spreading.

In this article, we explain the symptoms of each condition and how to tell them apart.

Nail psoriasis and nail fungus might look similar, but the causes, symptoms, and treatment are different.

Psoriasis

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Nail psoriasis causes lesions under the nail.

About half of all people with psoriasis exhibit symptoms of the condition on their nails.

Symptoms occur more frequently on the fingernails than the toenails.

Most people with lesions under or on the nails develop psoriasis symptoms elsewhere, too. In some people with psoriasis, nail symptoms are the first to appear.

Fungus

A person can pick up a fungal infection through physical contact with an object or surface that another person with a fungal infection has touched.

Nail fungi thrive in moist, warm environments. People whose hands or feet are often wet have a high risk.

However, people with a suppressed immune system, such as those with diabetes or HIV, may develop sores that do not heal after a fungal infection. Prompt treatment is essential for this reason.

Quickly starting treatment will yield better results and reduce the risk of a severe infection. Any delay in treatment may permanently damage the nail bed.

Here, learn more about nail fungus.

A few specific clues may suggest that psoriasis is the problem and not a fungal infection.

Some telltale signs of fingernail and toenail psoriasis include:

Other psoriasis symptoms

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Psoriasis may lead to red, scaly skin.

When other symptoms of psoriasis accompany lesions on the nails, symptoms are likely to indicate that psoriasis is affecting the nails too.

Symptoms of psoriasis include:

  • red, scaly, or peeling patches of skin
  • itchy, dry patches of skin
  • skin patches that open, bleed, and do not heal
  • smooth, raw-looking patches of skin
  • tiny bumps on the chest or back of the body
  • silvery-white patches on the skin

Different types of psoriasis produce different symptoms, and these may change or get worse over time.

Learn about the symptoms of psoriasis here.

Nail pitting

People with nail psoriasis develop a telltale pattern of yellowing nails with pits that continue to get deeper.

At the outset, the nails might look a little dry, then develop ridges that end up forming deep pits or even holes.

Nail loss

Psoriasis is more likely than a fungus to make the nails detach from their beds, leading to nail loss.

The nails may fall off entirely or break off in pieces. Before a nail falls off, a gap usually develops between the nail and the fingertip.

Fungal infections tend to change the shape and appearance of the nails but rarely cause the nails to fall off.

Nail color and structure changes

Keratin is a protein that promotes the development of the skin and nails. Nail psoriasis sometimes causes too much keratin to grow under the nail. This overgrowth is called subungual hyperkeratosis.

People with hyperkeratosis may notice a white, chalky substance under the nail. When this occurs in the toenails, the pressure of shoes pushing down on the nails might cause pain.

Recent trauma

Symptoms of nail psoriasis often appear after an injury in the affected area. It is possible to overlook a small injury, such as a cut or bruised toe because people sometimes cram their feet into tight shoes or expose them to the ground.

Psoriasis symptoms may also flare up after the following:

  • breaking or damaging a nail
  • a painful hangnail
  • slamming a finger in a door
  • experiencing an injury from a pedicure or manicure

While an open wound on the hands or feet makes it easier for fungal infections to enter the body, the wound will not directly trigger a fungal infection.

Most people with fungal infections do not experience an injury before the infection begins.

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Nail fungus looks different to psoriasis.

Fungal infections usually affect the toes, not the fingernails. This is because the feet are more likely to come into contact with fungus when walking barefoot.

People who get regular manicures or whose hands are often wet, however, are equally vulnerable to fungal infections of the fingernails.

Some characteristics of fungal infections of the nails include the following.

Nail color

Fungal infections can cause hyperpigmentation, or changes in the color of the nail.

The infection may begin as a faint gray, greenish, or brown spot that gets darker and wider over weeks or months.

Psoriasis does not typically cause dark spots on the nail.

Nail shape

Unlike psoriasis, fungal infections do not cause pits in the nails. Instead, the nails tend to change shape over time. They may become thin or develop thick patches and sometimes break.

Nail growth pattern

Nail fungus often grows with the nail. It attaches to a specific portion of the nail, and as the nail grows and that portion of the nail moves, so too does the fungus.

As the fungus tends to spread, though, this pattern can be hard to detect.

Spreading

Both psoriasis and fungal infections tend to get worse with time. Psoriasis, however, does not spread through contact in the same way as a fungal infection.

People with a fungal infection of the toenails may notice color changes between the toes, or other signs that the infection has spread to the skin between the toes.

The infection may also eventually spread to the fingernails or from one toe to multiple toes.

Knowing the difference between nail psoriasis and nail fungus can prevent people with fungal infections from spreading it to others. However, people with nail symptoms from either condition should not self-diagnose.

Psoriasis and fungal infection are not mutually exclusive. It is possible to have both at the same time.

People with psoriasis may also be more vulnerable to fungal nail infections. This can complicate the process of getting an accurate diagnosis.

Only a doctor can confidently determine the cause of any changes in the fingernails and toenails. Prompt medical care can address symptoms of both nail psoriasis and nail fungus.