Symptom guide
Nail changes: causes, red flags and when to get it checked
Nails grow slowly and carry a record of recent injury, infection and general health. Ridges, pitting, thick yellow nails, spoon shapes and dark streaks each have different explanations. Most are harmless, but a new dark line under a single nail, or a nail that changes after injury and does not recover, should be assessed to exclude melanoma.
Last checked: 2026-10-03
Key facts
At a glance.
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Fungal infection
Thick, yellow, crumbly nails, usually toenails, are most often fungal, though psoriasis can look similar.
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Pitting
Tiny pits in the nail suggest psoriasis or eczema.
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Dark streak
A new dark line under one nail, especially widening or with skin pigment spreading, should be checked urgently.
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Spoon shape
Concave "spoon" nails can reflect iron deficiency.
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Who to see
GP, podiatrist or dermatologist; urgent referral for suspected melanoma.
What this symptom usually means
The nail plate is made by the nail matrix under the cuticle. Disease or injury at the matrix changes how the nail forms, while disease of the nail bed alters its colour and attachment. Because nails grow around 3 mm a month (fingernails) and slower in toes, changes can reflect events from months before.
Possible causes, from most to least common
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Injury: bruising under the nail, ridging or deformity after trauma or repetitive pressure from footwear.
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Fungal nail infection (onychomycosis): thickening, yellow-brown discolouration, crumbling, lifting.
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Psoriasis: pitting, oil-drop discolouration, thickening and lifting; may accompany skin or joint disease.
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Ageing and eczema: longitudinal ridges and brittle nails.
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Iron deficiency (spoon nails, brittle), thyroid disease and nutritional deficiency.
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Paronychia: red, swollen, painful nail fold from infection around the nail, often from wet work.
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Lichen planus, alopecia areata and other skin disease, medicines such as chemotherapy, and systemic illness (Beau lines, clubbing).
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Subungual melanoma or other tumours: a dark band, a non-healing nail lesion or pigment spreading onto the skin.
Features that point to something more serious
A new dark line or band in one nail, a band that widens, blurs or spreads to the skin, nail destruction without injury, a bleeding or non-healing lesion, clubbing of the fingers, painful swelling with pus, and nail changes with joint pain or skin disease need assessment.
Red flags: when to seek help
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Urgent GP referral: a new, changing dark streak under a nail, or a nail lesion that does not heal.
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Same-day GP: a hot, painful, swollen nail fold with pus or red streaks spreading from the nail, particularly in diabetes.
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GP within weeks: nail changes with joint pain, skin rash or clubbing.
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Routine: thickened, discoloured or ridged nails you want assessed.
What a doctor will ask and examine
The doctor asks which nails, how long, injury, footwear, wet work, medicines, skin and joint disease, family history and diabetes. They examine all nails, skin and joints, may use a dermatoscope, and take clippings for tests.
Tests that are commonly used and why
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Nail clippings for fungal microscopy and culture: confirm infection before treatment.
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Dermoscopy of the nail: assess pigmented bands.
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Nail matrix biopsy: for suspected melanoma or unexplained nail disease.
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Blood tests: full blood count, ferritin, thyroid and glucose.
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Joint and skin assessment if psoriasis is suspected.
Self-care and the usual route
Keep nails short and clean, wear well-fitting shoes, avoid trauma and biting, protect hands from prolonged wet work and moisturise the cuticle area. Do not self-treat suspected fungal nails without confirmation, since several conditions look alike. Fungal infection may need months of treatment with topical or oral antifungal medicines or laser options.
The NHS route is a GP or podiatrist, with dermatology for complex or suspicious cases. Private podiatry and dermatology are available directly.
Frequently asked
Questions people ask.
Quick, plain-English answers to the questions we hear most.
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Why are my nails ridged?
Fine vertical ridges are common with ageing. Horizontal grooves suggest a past illness or injury interrupting growth.
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How do I know if it is fungus?
Thick, yellow, crumbly nails suggest fungus, but psoriasis can mimic it. Clippings tested in a laboratory confirm it.
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What does pitting mean?
Small pits in the nail are typical of psoriasis and sometimes eczema or alopecia areata.
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Is a black line under a nail dangerous?
Often benign, especially in darker skin, but a new, single, widening or irregular band needs urgent review to exclude melanoma.
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Can iron deficiency affect nails?
Yes. Brittle, spoon-shaped nails can reflect iron deficiency, among other causes.
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Do supplements like biotin help?
Evidence is limited and biotin can interfere with some blood tests, so tell your clinician if you take it.
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How long do nail changes take to resolve?
Fingernails take about 4 to 6 months to regrow and toenails 12 to 18 months.
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Can nail changes signal a general illness?
Sometimes. Clubbing, spoon nails, pale nails and pitting can accompany conditions elsewhere in the body.
Where this comes from
Sources and checking.
This guide is for information, not medical advice.
Your GP or consultant knows your history and can tell you which parts apply to you. If your symptoms are severe, rapidly worsening, or come with red-flag features, seek urgent medical care. Figures and availability change, so treat them as a guide and confirm with the provider.
Published 2026-10-03, next review 2027-10-03.
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NHS: Fungal nail infection (nhs.uk/conditions/fungal-nail-infection/)
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NHS: Psoriasis (nhs.uk/conditions/psoriasis/)
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NHS: Melanoma skin cancer (nhs.uk/conditions/melanoma-skin-cancer/)