Nails change slowly and most of the changes are harmless: a white fleck, a faint ridge, a stain after a red polish. A small number are the first visible sign of something that needs treatment, because the plate keeps a record of the months in which it grew. The rule is short: a change you can explain can usually wait, a change you cannot explain should be looked at.
The NHS, the American Academy of Dermatology (AAD), the British Association of Dermatologists (BAD) and DermNet each publish lists of nail warning signs, and they overlap. One sign, a new dark streak under a nail, outranks all the others, because the nail is one of the places where melanoma is found late.
Which nail changes need a doctor?
The NHS asks people to see a GP if a nail has changed shape, changed colour or fallen off and they do not know why, or if the skin around the nail has become sore, red, swollen and warm, which can be a sign of infection (NHS). The AAD publishes twelve nail changes a dermatologist should examine, from a dark streak to spoon-shaped and curved nails (AAD).
| Sign | May mean | Who to see | How soon |
|---|---|---|---|
| New or changing dark streak under a nail | Melanoma of the nail unit; also a benign mole, an injury or a medicine | GP for urgent referral, or dermatologist | Within days |
| Nail lifting from the bed, white or yellow at the tip | Onycholysis from trauma, psoriasis, fungus or thyroid disease | GP | Weeks; sooner if green or painful |
| Red, swollen, warm or pus-filled nail fold | Paronychia, a bacterial or fungal infection | GP, same day if spreading | Days |
| Greenish-black nail | Pseudomonas bacteria under a lifted nail | GP | Days |
| Small pits like pin pricks | Nail psoriasis, eczema, alopecia areata | GP, then dermatologist | Weeks |
| Thick, crumbly, yellow nail from the edge | Fungal infection | Pharmacist, then GP | Weeks |
| Grooves across all nails at the same height | Beau's lines after illness, fever or chemotherapy | GP if no illness explains them | Weeks |
| Spoon-shaped, thin nails | Iron-deficiency anaemia | GP for a blood test | Weeks |
| Clubbed nails curving over swollen fingertips | Heart, lung, liver or bowel disease | GP | Within a week or two |
| Pain under the nail, or a bump lifting the plate | Injury, a small growth, a bone spur | GP | Weeks; same day after a heavy blow |
Small white spots, faint vertical ridges and a stain after dark polish need no appointment; they are almost always harmless and grow out. The ordinary changes are covered in the nail care guide.
What does a dark streak under a nail mean?
A dark streak is a brown or black band running from the cuticle to the tip. DermNet calls it melanonychia and lists the common harmless causes: a mole in the matrix, natural pigmentation, which affects nearly all people of Afro-Caribbean descent by the age of 50 and up to 20% of Japanese people, injury from biting or footwear, and medicines including some chemotherapy drugs (DermNet, melanonychia). Most bands are benign. The one that is not is melanoma.
The AAD guide to checking nails for melanoma names the warning signs: a dark streak, often on the thumb or big toe; skin next to the nail turning darker, a sign of advanced disease; the nail lifting from the bed; a nail splitting down the middle; and a bump or nodule under the nail. Nail melanoma is more common in older people and people with skin of colour (AAD, nail melanoma).
- A band on one nail only, in an adult, is more suspicious than bands on several nails.
- A band that is widening, darkening or blurred at the edges is more suspicious than one unchanged for years.
- Pigment spreading on to the skin of the cuticle or fingertip needs a dermatologist at once.
- A bruise moves towards the tip as the nail grows; a melanoma band stays anchored at the cuticle.
The AAD advice is that anyone who notices a new dark band on a nail should see a board-certified dermatologist. In the Netherlands and the UK the GP is the first step and can refer urgently.
Why is a nail lifting from its bed?
Onycholysis is the separation of the nail plate from the nail bed, which shows as a white or yellow area at the tip that spreads back. DermNet lists the causes: repeated trauma, including manicures and long soaking; psoriasis, lichen planus and hand dermatitis; fungal infection; thyroid disorders, diabetes and pregnancy; and medicines such as tetracycline antibiotics, some anti-inflammatories and oral retinoids, sometimes with sunlight as the trigger (DermNet, onycholysis).
The lifted space matters more than the lift. Water collects under the plate and the bacterium Pseudomonas aeruginosa can grow there, turning the nail green or greenish-black, which the AAD lists as a sign of bacterial infection. DermNet's management is to clip the loose part and keep the nail short, avoid polish and solvents on it, wear gloves with cotton liners for wet work, and treat the cause. The bed reattaches only as new nail grows: fingernails take four to six months, toenails twice as long.
The AAD also lists nail lifting among the signs of nail melanoma, so a lifted nail with a dark band, or one with nothing to explain it, is a reason for a dermatologist.
What do pits, thickening and yellow nails point to?
Pitting is small dents in the surface of the plate, which the AAD describes as dents that look as if they were made by an icepick. The NHS lists nail psoriasis, eczema and alopecia areata as the causes. DermNet reports that nail psoriasis affects up to 80% of adults with psoriasis at some point, with pitting, lifting, oil-drop patches and crumbling as the signs, and notes that psoriatic nail disease may be a risk factor for psoriatic arthritis (DermNet, nail psoriasis). Pitted nails and sore joints should be mentioned together to the GP.
Thickening with yellow or white colour from the free edge is the pattern of a fungal infection. The NHS describes fungal nails as brittle, discoloured or thicker than usual, notes that the infection usually starts at the edge and can lift the whole nail, and says a pharmacist can supply an antifungal lacquer while a GP can prescribe tablets when that fails or when the person has diabetes or a weak immune system (NHS, fungal nail infection). Yellow nails that thicken and stop growing on all fingers and toes are rarer, point to yellow nail syndrome, and need a GP.
What are the signs of a nail infection?
Paronychia is inflammation of the skin around one or more nails. Acute paronychia develops over a day or two after a hangnail, a bitten cuticle or a manicure cut: the fold turns red, swollen, hot and painful, and pus may collect beside the nail. Chronic paronychia, per the BAD, lasts more than six weeks and follows repeated wetting and irritants; the fold is swollen and tender and pus-filled blisters may be white, yellow or greenish (BAD, chronic paronychia).
- Redness and swelling around the nail: the AAD notes that early treatment with soaks and antibiotics works best.
- Pus beside or under the nail, or a red streak up the finger, which needs a GP the same day.
- A green or black colour under a lifted nail.
- Fever, or any infection in someone with diabetes or poor circulation, which the BAD flags for prompt care.
The BAD self-care for chronic paronychia is to keep the hands warm and dry, wear gloves for water and chemicals, avoid manicures and biting, and leave polish off until the fold has healed. Prevention is set out in nails, water and household cleaning.
What will a GP or dermatologist check?
- History: when the change started, which nails, any injury, illness, new medicines, gel or acrylic wear, psoriasis or eczema in the family, and symptoms elsewhere such as tiredness or joint pain.
- All twenty nails, with polish removed, plus the skin, scalp and joints, because one nail rarely tells the whole story.
- Dermoscopy: a hand-held magnifier with a light, used on a dark band to judge its width, colour and edges.
- Nail clippings sent for fungal testing when infection is suspected, since fungus and psoriasis can look alike and are treated differently.
- Blood tests where the pattern suggests them: iron for spoon nails, thyroid function for brittle ridged nails, glucose if paronychia keeps returning.
- A biopsy of the matrix for a suspicious band. This is the only way to confirm or exclude melanoma, and a dermatologist does it under local anaesthetic.
Treatment follows the finding: antifungal lacquer or tablets, a steroid for psoriasis, antibiotics or drainage for infection, a change of medicine, or referral to a skin cancer team. Results are slow because the plate is slow to grow; DermNet notes that psoriasis treatment takes weeks or months to show.
How do you prepare for a nail appointment?
You will need
- Polish-free nails on all fingers and toes, removed the day before
- Photographs of the nail taken every few weeks, with a date, to show change
- A list of medicines and supplements, including biotin
- Dates of any recent illness, fever, operation or injury
- Notes on gel, acrylic or dip use in the past year
Bare nails matter most, because a band or a pit cannot be assessed through lacquer. Before a visit for a possible infection, leave the nail fold alone: no cutting, no pushing, no soaking, and no antiseptic that colours the skin.
The three commonest cosmetic complaints are covered in ridges on nails, white spots on nails and yellow nails after polish.
- A new or changing dark streak under a nail needs a dermatologist within days, because it can be melanoma; the AAD and DermNet both rank it first.
- See a GP when a nail has changed shape or colour for no reason you know, or when the nail fold is red, swollen, warm or painful.
- Lifting, pitting, thickening from the edge and grooves across all nails usually have ordinary causes, but each one deserves a check.
- A GP or dermatologist looks at all twenty bare nails, may send clippings for fungal testing, may run blood tests, and biopsies a suspicious band.
- Go with polish off, dated photographs and a list of medicines.
Questions people ask
When should I see a doctor about my nails?
When a nail has changed shape or colour and you do not know why, when the skin around it is sore, red, swollen and warm, or when a new dark streak has appeared. The NHS and the American Academy of Dermatology both give those three triggers. A dark streak should be seen within days.
Is a dark line under a nail always melanoma?
No. Most dark bands are a mole in the matrix, natural pigmentation, an old injury or a medicine effect. A band that is new, on one nail only, widening, darkening or spreading on to the skin is the one to worry about, and only a dermatologist can tell, sometimes with a biopsy.
Should I see a GP or a dermatologist for a nail problem?
In the Netherlands and the UK, the GP first. A GP can diagnose fungal infection, paronychia and iron deficiency, prescribe treatment, and refer urgently for a suspicious dark band or for psoriasis that needs specialist care. Toenail problems can often go straight to a podiatrist.
What does a nail lifting from the nail bed mean?
Onycholysis. The common causes are repeated trauma, psoriasis, fungal infection, thyroid disease and some medicines. Keep the nail short and dry and see a GP if it spreads, turns green or has no clear cause, because a lifted nail can also be a sign of melanoma.
Do I need to remove nail polish before a dermatologist appointment?
Yes, on all fingers and toes, the day before. A dermatologist assesses colour, pits and bands on the bare plate. Bring dated photographs of the change and a list of your medicines and supplements.
- NHS, Nail problems
- American Academy of Dermatology, 12 nail changes a dermatologist should examine
- American Academy of Dermatology, How to check your nails for melanoma
- DermNet, Melanonychia
- DermNet, Onycholysis
- DermNet, Nail psoriasis
- NHS, Fungal nail infection
- British Association of Dermatologists, Chronic paronychia