Toenail Fungus or Nail Trauma? Thick, Discoloured Nails Explained

A big toenail that has become thick, ridged and yellowish is easy to label as "fungus". Sometimes that's right. But many discoloured, thickened nails turn out not to be fungal at all. One of the most common look-alikes is nail trauma: damage from an injury or from months and years of pressure inside your shoes.

This article focuses on thick, discoloured nails. If your main worry is a dark red, purple or black patch, our article on toenail fungus or a bruise covers that, including the warning signs that need prompt attention.

How injury changes a toenail

A toenail grows from the matrix, a pocket of tissue hidden under the skin at the base of the nail. If the matrix or the nail bed is damaged, the nail that grows afterwards may be thicker, uneven, ridged, discoloured or only loosely attached. In some cases the change is permanent.

One big injury

Dropping something heavy on your foot, stubbing a toe hard, or a skate or cleat stepping on it can cause bleeding under the nail. The nail may loosen and fall off. When it grows back, it can come in thicker or misshapen. The AAD notes that a toenail can take 12 to 18 months to grow back fully, so the after-effects of one injury can be visible for a long time.

Repeated small injuries

Far more often, the damage builds up slowly. Every step in a shoe that's too tight, too short or too loose lets the toes bump the front of the shoe. Over thousands of steps, that repeated pressure can thicken and loosen the nail. Common culprits include:

• Running, hiking (especially downhill), tennis, soccer and dancing
• Tight hockey skates, ski boots or work boots
• Shoes with a narrow or shallow toe box, or high heels
• Toe shapes that press against the shoe, such as bunions or hammertoes
• A big toe that's longer than the others, or the way your foot lands when you walk

Because it happens gradually, many people don't link the nail change to their footwear or activity at all.

What a trauma-damaged nail tends to look like

• Often affects one or both big toenails, or the toe that takes the most pressure in your shoes.
• May be thick, ridged or curved, sometimes with lifting at the tip.
• Discolouration may be whitish where the nail has lifted, or dark if there's been bleeding.
• Often matches a known injury or a pressure point, and may be similar on both feet.
• Tends to stay roughly the same over time rather than steadily spreading.

What a fungal nail tends to look like

• Usually starts at the tip or side edge and slowly spreads back towards the cuticle.
• White, yellow or yellow-brown discolouration.
• Crumbly or brittle, with chalky debris building up under the nail.
• May spread to other toenails over time.
• Often linked with athlete's foot, sweaty feet, or barefoot walking in shared showers and change rooms.

Why it's hard to tell by looking

The lists above describe typical patterns, but real nails rarely read the textbook. A lifted, thickened nail from shoe pressure can look yellowish and crumbly. A fungal nail can be ridged and misshapen. The American Academy of Dermatology (AAD) specifically notes that a nail injury can sometimes look like nail fungus.

To make things more complicated, the two often happen together. Both the AAD and the Canadian Dermatology Association list nail injury as a risk factor for fungal infection. A damaged, lifted nail leaves gaps where fungi can settle, so an old injury can later become a fungal nail.

This is where a test earns its keep. Instead of guessing, a qPCR DNA test of a nail clipping tells you whether fungal DNA is present. That doesn't explain everything about your nail, but it answers the most important question before you start treatment.

Why the cause changes what you do

If it's trauma alone, antifungal products won't change the nail, no matter how long you use them. Care focuses on reducing pressure and keeping the nail comfortable:

• Shoes with enough length and a roomy, deep toe box. Feet tend to swell later in the day, so that's a good time to shop for shoes.
• Lacing that stops your foot sliding forward, particularly for running and hiking.
• Trimming nails straight across and not too short.
• Moisture-wicking socks, changed daily.
• A podiatrist or chiropodist can safely thin a thick nail and look at footwear, orthotics or foot shape.

If fungus is involved, a healthcare provider can talk you through treatment options (see our overview of treatment options in Canada), and reducing pressure on the nail still helps.

When to get checked promptly

• A dark streak or dark spot with no clear injury, or one that doesn't grow out.
• Severe pain or pressure under a nail after an injury, or a possible broken toe.
• Redness, warmth, swelling or pus around the nail.
• You have diabetes, poor circulation or a weakened immune system. Even a minor nail injury deserves attention (see toenail fungus and diabetes).

Find out before you spend months treating

If you have a thick, discoloured toenail and aren't sure whether it's trauma, fungus or both, testing gives you a clearer starting point. Our at-home kit includes everything you need to clip a sample and mail it back in the prepaid envelope. Your sample is analysed with qPCR DNA testing, reviewed by a licensed Canadian podiatrist with over 50 years of experience, and your report arrives 4–14 days after your sample reaches us.

A negative result can help point you and your healthcare provider towards trauma or another cause, though it isn't a diagnosis on its own. Read understanding your results to see what each outcome means, or look at a sample report.

Frequently asked questions

Can a toenail stay thick forever after an injury?

Sometimes. If the area at the base of the nail that makes new nail was damaged, the nail can keep growing thick or misshapen. Other times it gradually returns to normal as new nail grows out. A podiatrist or chiropodist can help manage a nail that stays thick.

How long does it take a toenail to grow back after an injury?

Toenails grow slowly. The American Academy of Dermatology notes that a toenail can take 12 to 18 months to grow back after it's removed, so changes from an injury can be visible for a long time.

Can running make my toenails thick and discoloured?

Yes. Repeated pressure from toes hitting the front of the shoe can bruise, thicken and loosen toenails, especially on long runs or downhill hikes. Shoes with enough length and a roomy toe box can help.

Will antifungal treatment fix a nail damaged by trauma?

Antifungal treatments only work on fungal infections. If the change is caused by injury alone, they won't improve it. That's why it helps to find out whether fungus is involved before starting a long course of treatment.

Can an injured toenail get a fungal infection?

Yes. Nail injury is a known risk factor for fungal nail infection, because a damaged or lifted nail gives fungi a place to settle. If an injured nail starts turning yellow, crumbling or spreading, consider getting it tested.

Sources

• American Academy of Dermatology: Nail fungus diagnosis and treatment
• American Academy of Dermatology: Nail fungus, causes
• American Academy of Dermatology: 12 nail changes a dermatologist should examine
• Canadian Dermatology Association: Nail fungus and infection
• Mayo Clinic: Nail fungus, symptoms and causes
• NHS: Fungal nail infection