Have you noticed your nail growing back differently after it was injured or lost? Maybe it’s coming in thicker than before, has an odd color, or is crumbly, bumpy or ridged. While it might seem like a small issue, changes in how your nails grow back can be a sign of something more serious.

Rachit Shah, DPM, a podiatrist at Northwestern Medicine, provides an in-depth look into seven common causes of irregular nail regrowth:

Trauma or Injury

A hard bump, crush injury or repeated pressure (like from tight running shoes, which is sometimes called “runner’s toe”) can damage your nail matrix. In the medical field, this is known as a subungual hematoma. Your big toe is the one most often injured, and if you have a sudden injury, your toe may be very painful.

“Oftentimes, it’s a microtrauma from your shoe gear in everyday life versus blunt trauma that causes irregular nail growth,” says Dr. Shah.

Trauma or injury can lead to a nail growing back:

• Thicker than normal
• Curved or ridged
• Discolored, typically black and blue from bleeding under the nail

According to Dr. Shah, trauma can also turn your nails yellow around the edges.

Fungal Infection (Tinea Unguium or Onychomycosis)

Fungal infection is a common cause of irregular nail regrowth. Symptoms may include:

• White, yellow or brown discoloration
• Thickened, crumbly texture
• Separation from the nail bed
• Curled down, distorted shape
• Foul odor

Fungi thrive in warm, moist places like shoes, socks, locker rooms and showers, and can enter the nail through small cracks in your nail or the skin around your nail. This makes your toenails more vulnerable to infection.

“Usually from what I see in my clinic is that if you have fungal infection on one toe, there's a pretty high probability that you're going to develop it on adjacent toes or both of your feet,” says Dr. Shah. “Very rarely I see that if one person has a fungal infection that another person will pick it up. It’s not that type of contagious infection where we all have to have our toes covered at all times. It's more prone to spread from one toe to another versus one person to another.”

Bacterial Infection (Paronychia)

This skin infection around your nail is caused by bacteria. It typically develops faster than a fungal infection and can impact your nail’s growth. Similar to fungal infections, bacteria can enter the skin and nails through small cracks, often from nail biting or picking, as well as manicures and pedicures done with unsanitary tools or water.

Symptoms may include:

• Redness and swelling
• Pain
• Warmth
• Pus formation
• Foul odor

Health Conditions

Psoriasis

Psoriasis is a chronic autoimmune condition that can affect the skin, joints and nails. Nail psoriasis may cause:

• Pitting (small dents in the nail surface)
• Thickened, rough nails
• Yellow-red discoloration (known as the “oil drop” sign)
• Nails lifting from the nail bed

Lichen Planus

Lichen planus is a chronic inflammatory skin condition that can affect the nails, causing:

• Thinning or splitting
• Ridges and grooves
• Permanent loss of the nail

Diabetes, Peripheral Artery Disease

Conditions that cause poor circulation like diabetes or peripheral artery disease can affect nail growth. Reduced blood flow means your nail matrix may not get enough oxygen or nutrients, leading to:

• Grooved lines that run across the nail (known as Beau’s lines)
• Slower nail growth
• Discoloration
• Higher risk of fungal infection

Aging

As you age, the growth of your nails slows down. This can lead to:

• Yellow or opaque color
• Thickening, especially in the toenails
• Brittleness, especially in the fingernails, and fraying on fingernail tips
• Ridges running the length of the nail

These changes are usually harmless but can be worsened by other health conditions.

Nutrient Deficiencies

Lack of key nutrients, such as biotin (vitamin B7), iron, zinc or protein, can affect your nail growth. Deficiency-related signs include:

• Weak or brittle nails
• Ridges or grooves
• Pale or oddly colored nails

Chemical and Moisture Exposure

Frequent use of nail products like acetone, gel polish or acrylic nails, or constant moisture exposure from activities like swimming or frequent dishwashing, can irritate your nail and lead to:

• Softening, weakening and peeling
• Brittleness
• Discoloration

This is often temporary but can be permanent if your nail matrix is significantly damaged.

How long does it take for a nail to grow back?

Nails grow slower than a snail’s pace. On average:

• Fingernails grow about 3.4 mm per month
• Toenails grow even slower — about 1.6 mm per month

Even when there is no damage to the nail matrix, it can take up to six months for a fingernail to fully grow back and up to 18 months for a toenail. If there is damage, growth can be much slower or stopped.

When to See a Doctor About Nail Changes

Some nail changes are harmless and go away over time. But if your nail is…

• Painful or swelling
• Emitting an odor
• Changing color over time
• Detaching from your nailbed
• Growing in thick, brittle or misshapen
• Not improving over several weeks

…it’s a good idea to see your primary care physician or a specialist like a dermatologist or podiatrist. A medical professional can check for infection, injury or underlying health problems and recommend treatment, if needed.

Common treatment options include:

• Antifungal medication (oral or topical) if a fungal infection is confirmed
• Antibiotics (oral or topical) if a bacterial infection is confirmed
• Prescription creams or systemic treatments for psoriasis or other skin conditions
• Proper hygiene to keep nails trimmed, filed, dry and clean
• Protective footwear to reduce trauma and moisture buildup
• Healthy diet rich in fruits, vegetables, and plant-based and lean-meat proteins

“There are so many topical treatments out on the market for fungal nail infections. And, I'll be honest, there are not a lot of good ones,” says Dr. Shah. He explains that for these treatments to work, they need to seep through the layers of a nail. “When a nail is really thick, the medication has a hard time penetrating all the way down to the base of your nail,” he says.

Dr. Shah notes that some small studies suggest over-the-counter topical products containing menthol, like Vicks VapoRub™, may help soften the nail and inhibit the growth of fungus. He adds that the prescription oral medication terbinafine is much more effective than over-the-counter treatments but can cause side effects that must be monitored, including liver damage. Even after a course of terbinafine is completed, Dr. Shah says nail fungus typically comes back. It’s stubborn!

If nail fungus is not causing you pain and is more of a cosmetic problem, Dr. Shah recommends just keeping your nail clean, dry and trimmed. “Some people can live with nail fungus for a lifetime,” he says. For more severe cases that do cause pain, he says nail removal may be necessary.

If the cause of your nail change is unclear, biopsy or lab testing may be recommended by your physician. This can help determine if you have a fungal infection or a bacterial infection, and rule out skin cancer under the nail.