Nail discolouration

What is nail discolouration, and how common is it?

Nail discolouration (chromonychia) is any change in the colour of a fingernail or toenail. It has many causes, from knocks and nail cosmetics to fungal infection, medicines and, sometimes, an underlying health condition¹.

Nail changes are common, especially in older adults², and most are harmless³. Small white spots are the most common white change, particularly in children, and are usually from minor knocks⁴.

What can cause it?

The colour and pattern give clues, but they're only clues.

• Yellow: most often fungal infection or nail psoriasis⁵. Fungal infection also tends to thicken the nail⁶.
• Green-black: can be a bacterial infection, particularly under a loose nail⁵.
• White: surface white marks can come from fungal infection or nail cosmetics, such as artificial nails and frequent polish remover⁴. Widespread white nails can occasionally point to a liver or kidney problem⁴.
• Brown or black: blood under the nail after an injury grows out with the nail, leaving normal nail between the dark patch and the cuticle⁷. Brown-black bands are common and usually harmless in people with darker skin⁸, and almost all dark nail colour in children is harmless⁹. Melanoma (a skin cancer) of the nail is rare, but it's the cause that mustn't be missed⁷.
• Medicines and chemicals: hair dye, nail varnish, nicotine and some medicines can discolour nails¹⁰.

How is the cause found?

A podiatrist looks at all your nails, the nail folds and the skin around them before naming a cause¹¹. They'll ask when it started, and about injuries, medicines and nail products. For a dark band, they'll also ask about past or family skin cancer and check your skin⁷.

Magnified examination (dermoscopy) can help tell blood from pigment⁸. It can't confirm or rule out melanoma, so a suspicious band needs a doctor's assessment, and any biopsy decision sits with a doctor²⁷. If fungal infection is suspected, nail clippings sent to a laboratory can confirm it². Widespread white nails may need blood tests⁴.

What helps first?

Treatment depends on the cause¹². It helps to avoid starting an antifungal for a nail that's only discoloured: confirm the cause first.

• White spots from knocks or cosmetics: gentle nail care. Avoid pushing back cuticles, and limit polish, remover, artificial nails and nail glue⁴.
• Fungal infection: options include antifungal paint-on treatments or tablets, and trimming and shaping by a podiatrist¹². In adults with fungal toenails, prescribed antifungal tablets work better than a dummy tablet¹³. They can interact with other medicines and, rarely, harm the liver, so a doctor needs to prescribe and monitor them¹³. Talk to the prescriber first if you're pregnant, may become pregnant or are breastfeeding. This finding is from adults with toenail infection, so it may not carry over to fingernails or children¹³.

What helps if that isn't enough?

If a fungal nail isn't responding, or the cause is unclear, it's worth having the diagnosis reviewed by a doctor or dermatologist (a skin doctor) rather than repeating the same treatment¹⁴. In adults, a continuous course of antifungal tablets gave better odds of clearing the infection than paint-on treatments¹⁵. Lasers have limited effectiveness for fungal toenails¹⁶.

If you have diabetes, laser is best avoided, and surgical nail removal is generally avoided because of the risk of infection and ingrown nails. Medicines and gentle removal of thickened nail are preferred¹⁷.

Will it clear up, and can I stop it coming back?

It depends on the cause. Harmless causes have a good outlook: most single dark bands in adults are harmless pigment activity⁸, and darkening linked to a medicine typically fades slowly after the medicine is withdrawn⁸. Ask your doctor or pharmacist before changing any medicine.

Fungal infection can come back. Commonly advised steps are treating athlete's foot promptly, keeping feet dry and cool, avoiding bare feet in communal wet areas, and replacing or cleaning old footwear. How much each step lowers the chance of it returning isn't clear yet.