Fungal nail infection

What it is

Fungal nail infection (onychomycosis) makes nails thick, white, yellow or brown, brittle and sometimes lift from the nail bed. Toenails are affected far more than fingernails.

How it works

Fungi — usually the same dermatophytes that cause athlete's foot — get under the nail and digest keratin, making nails thick, yellow-white and crumbly. Because nails grow slowly, the infection is slow to clear.

Why it matters on darker skin

Heat, humidity, closed shoes and shared footwear or salon tools make fungal infections common. On darker skin, brown discolouration needs to be told apart from pigment streaks.

Causes and triggers

Athlete's foot, sweaty enclosed shoes, communal showers, nail trauma, diabetes and older age.

What helps — and why it works

A doctor can confirm it with a nail clipping, because other conditions look similar. Mild cases may respond to medicated nail lacquer; more extensive infection often needs tablets. Nails grow slowly, so a clear nail may take 6 to 12 months (toenails) to appear. Keep feet dry and treat athlete's foot too. Confirm the diagnosis: psoriasis and trauma look similar; a nail sample confirms fungus. Expected timeline: results within weeks. Amorolfine or ciclopirox lacquer for mild cases: penetrates the nail to reduce fungus. Expected timeline: 6–12 months. Tablets for extensive cases: reach the nail from the blood. Expected timeline: toenails take 12–18 months to grow out clear. Treat athlete's foot too: prevents reinfection. Expected timeline: 2–4 weeks.

What to avoid and why

Avoid sharing nail tools and towels, and walking barefoot in communal showers. Avoid covering an infected nail with gel or acrylic.

Common mistakes

• Expecting results in weeks.
• Using bleach or vinegar soaks.
• Sharing nail tools.

Everyday nail habits

Healthy nails depend on protecting the nail matrix — the growing area hidden under the cuticle — and on limiting cycles of wetting and drying. Wear gloves for washing and cleaning, keep nails short and filed in one direction with a fine file, and moisturise hands, nails and cuticles after washing and at night. Leave the cuticle in place: it is a seal that keeps water and germs away from the matrix, and cutting it is a common cause of infection. Fingernails grow about three millimetres a month and toenails about one, so a new fingernail takes four to six months and a toenail up to eighteen months; any treatment needs at least that long to judge. Choose salons that sterilise metal tools between clients, or bring your own. Take breaks between gel or acrylic sets, and never peel coatings off. Because polish can hide important changes, look at bare nails regularly, particularly for a new dark band, a lifted nail or a change in shape.

Products and treatments

Many nail products make claims with little evidence. Moisturisers containing urea, lactic acid or petrolatum have the most support for dry, brittle nails and cracked skin around them. Formaldehyde-based hardeners can make nails more brittle over time and can cause allergy, so we do not recommend them. Antifungal nail lacquers such as amorolfine or ciclopirox can help mild fungal infection limited to the tip of one or two nails, but only after the diagnosis is confirmed — many thick or discoloured nails are not fungal at all. Biotin supplements are widely sold; evidence is weak and high doses can interfere with some blood tests. If you have diabetes or poor circulation, foot and toenail problems deserve early professional care.

Questions to ask your doctor or pharmacist

Useful questions include: What do you think is causing this? Is it likely to come back, and how can I prevent it? Which products should I stop? How long before I should expect improvement, and when should I come back if it isn't better? Are there side effects to watch for? Is this treatment safe if I am pregnant, breastfeeding or for my child? Writing your questions down, bringing your products (or photos of their labels) and taking dated photos of the problem make an appointment much more useful.