Black toenail without a knock: causes and when to get it checked

A black toenail without a knock you can remember may be caused by small, repeated impacts from your shoes, but the colour alone does not tell you the cause. There are also infections and pigmentation changes that need a different kind of assessment. If the mark is new and you do not know why it appeared, book an appointment: do not start a fungal treatment just because the nail looks dark.

A new dark band, a change in colour of the skin around the nail or pigmentation that keeps changing should be assessed by a dermatologist. If there is also severe pain, a significant wound, pus or a fever, you may need prompt medical care.

Nothing needs to fall on your toe. The nail rubbing again and again against the shoe can damage tiny blood vessels and leave blood under the nail plate, which is the hard part you can see. That collection is called a subungual haematoma and can look reddish, purple, brown or almost black.

Context matters: a longer walk, a race, a steep descent or a change of trainers can help explain what happened. A trainer can be long enough and still press on the toe from above. That is a clue worth checking, not confirmation of a diagnosis.

Fungus can change a nail’s colour, thickness and texture. However, a dark or thickened nail does not prove an infection. When a fungal nail infection is suspected, a sample may need to be tested before certain treatments are chosen; fungal and bacterial infections explains how it is assessed.

There are also harmless pigmentation changes, effects of medicines and other nail conditions. Some less common causes need a specific dermatological assessment, and they cannot be told apart reliably by comparing your foot with a photo online.

If what is happening is that you have been using an antifungal for some time without improvement, you can read why nail lacquer for fungus sometimes does not solve the problem. That question is different from working out why a mark has just appeared.

Before your appointment, note when you first saw it, whether it affects one nail or several and whether it is changing. Mention any pressure from shoes, sport, a minor knock or recent treatment, and whether you take medication that may affect bleeding.

A photo in good light can help record how it changes so you can show it at the appointment, but do not wait months collecting photos if the mark has no clear cause. Do not scratch the surface or lift the nail to see what is underneath either.

The fact that it does not hurt does not mean it needs no assessment. And remembering some rubbing or a run does not rule out another cause on its own.

These situations point to the next step; they do not identify a condition on their own.

The American Academy of Dermatology advises checking new dark bands in the nails. Among the causes to rule out is nail melanoma, which is uncommon. It is mentioned to explain why an unexplained change should not be ignored, not to diagnose it by its appearance.

With diabetes, poor circulation or reduced sensation, get a new injury or change in your foot checked early, and if there is a wound, redness, warmth or discharge, do not wait for a routine check-up. Diabetic foot explains how check-ups are adapted to that risk.

Avoid shoes that squeeze or knock the toe and cut back on the activity that causes pain. If you need to change the way you walk to protect the nail, do not keep running to see whether it passes.

Keep the area clean and dry. If there is a small graze, clean it gently and protect it from rubbing with a clean dressing. Do not pull off a nail that is lifting or cut away a part that is still attached, and do not cover the mark with nail varnish before it can be examined.

Do not pierce the nail to let the blood out. When a recent haematoma causes pressure and pain, a professional can assess whether to drain it and whether there is another injury. Trying it at home with needles or hot objects can cause an infection or more damage.

The appointment starts with your history and an examination of the nail, the toe and your footwear. Depending on what is found, protecting the area and keeping an eye on it may be enough, or a test, a specific treatment or a referral may be needed.

If a pressure injury is suspected, it is worth checking where the toe hits and what has changed in the shoe or in your activity. Chiropody makes it possible to assess and care for troublesome nails, but not every dark nail is solved by cutting or thinning it.

When the findings point to a pigmented lesion, the next step may be dermatology. Drainage is not indicated for every black mark, and antifungal treatment is not indicated for every change of colour.

It depends on the cause and the damage. In a confirmed haematoma, the dark area usually moves towards the edge as the nail grows, and the visual recovery is slow. Pain improving sooner does not mean the mark will disappear straight away.

If a toenail is lost, growing back completely can take many months: the NHS says it can take up to 18 months. That timescale is not an invitation to watch an undiagnosed pigmentation on your own; at the appointment you will be told what to expect and when to have it checked again.

Bring the trainers you were wearing when the problem appeared, your usual socks and any insoles you use. Mention whether you changed distance, did more downhill or started to feel your toe touching the front of the shoe. That information is more useful than buying a bigger size without checking the fit.

Sports podiatry looks at the relationship between the foot, the activity and the footwear. Not every black toenail needs a gait assessment or insoles.

If your nails bother you in shoes or when walking, you can ask for an assessment at Clínica Podológica Seila Ivars, in Altea. The clinic reviews the request and confirms the appointment. For a new dark band or unexplained pigmentation, prioritise a medical or dermatological assessment, and with warning signs do not wait for a scheduled appointment.