Discoloured nails are a frequent pharmacy counter presentation. Most cases are fungal infections or post-traumatic changes — straightforward to manage with OTC products or simple reassurance. But nail colour changes can also signal psoriasis, medication effects, systemic disease, and, rarely, subungual melanoma. Knowing which patterns are safe to treat and which need urgent referral is an essential pharmacy skill.
The common causes
Yellow or white nails: fungal infection (onychomycosis)
This is the most common cause of nail discolouration presenting at the pharmacy counter. According to NICE CKS, fungal nail infections affect approximately 10% of the adult population. The typical appearance is:
- Thickened nail plate
- Yellow, white, or brown discolouration starting at the free edge or sides
- Crumbly, brittle texture
- Gradual progression over months
- Often associated with athlete's foot (tinea pedis)
Pharmacy management: OTC amorolfine 5% nail lacquer (Curanail, Loceryl) is appropriate for mild-to-moderate infections affecting up to two nails, with no more than 50% of the nail plate involved and no matrix (root) involvement. Treatment takes 6–12 months. Patients should be counselled that visible improvement takes at least 3 months as the healthy nail grows out.
Black or dark brown nails: trauma
A subungual haematoma — blood trapped beneath the nail plate following a blow or crush injury — is the most common cause of a dark nail. The patient can usually recall the injury. Key features:
- History of trauma (often sports, tight shoes, or dropping something on the foot)
- Colour that grows out with the nail over 6–9 months
- No widening of the discoloured band over time
- Proximal nail fold appears normal
Pharmacy management: Reassurance. The discolouration resolves as the nail grows out. If the haematoma is large and painful (seen acutely), the patient should be referred to a GP or minor injuries unit for possible trephination.
Green nails: bacterial infection
A green or green-black discolouration, often with a characteristic musty odour, suggests Pseudomonas aeruginosa colonisation. This typically occurs in nails that are already damaged — by fungal infection, trauma, or chronic moisture exposure. It is sometimes called "greenies" in nail salons.
Pharmacy management: Refer to GP. Pseudomonas nail infections require topical or oral antibiotics, depending on severity.
White spots or lines: minor trauma (leukonychia)
Small white spots or transverse white lines on the nail plate are almost always caused by minor trauma to the nail matrix. They are harmless and grow out.
Pharmacy management: Reassurance only.
The patterns that need referral
Longitudinal melanonychia: the line that must not be missed
A single dark brown or black longitudinal streak running from the cuticle to the free edge of the nail — longitudinal melanonychia — requires prompt referral. While it is often benign (particularly in patients with darker skin tones, where melanonychia is a normal variant), it can be an early sign of subungual melanoma.
Red flags for urgent two-week-wait referral:
| Feature | Significance |
|---|---|
| Single digit affected | More concerning than multiple digits |
| New onset in adults over 50 | Higher melanoma risk with age |
| Band wider than 3mm | Suspicious |
| Band widening or darkening over time | Suspicious for melanoma |
| Hutchinson sign (pigment extending onto the nail fold skin) | Strongly associated with subungual melanoma |
| Nail plate dystrophy (splitting, ridging, destruction) | Suggests invasion |
The British Association of Dermatologists (BAD) recommends that any new or changing longitudinal melanonychia in adults should be assessed by a dermatologist. Pharmacists who spot this pattern should refer urgently.
Nail changes suggesting psoriasis
Pitting (small dents in the nail surface), onycholysis (nail lifting from the bed), oil-drop discolouration (salmon-coloured patches), and subungual hyperkeratosis can all indicate nail psoriasis. This is relevant because nail involvement often correlates with psoriatic arthritis risk. Refer to GP for assessment.
Nail changes suggesting systemic disease
Some nail appearances are associated with underlying medical conditions:
- Koilonychia (spoon-shaped nails): iron deficiency anaemia
- Clubbing (curved nails with bulbous fingertips): lung disease, heart disease, inflammatory bowel disease
- Terry's nails (white nails with a narrow pink distal band): liver cirrhosis, heart failure
- Beau's lines (transverse grooves): severe illness, chemotherapy
These findings in isolation do not diagnose disease, but they should prompt a GP referral for investigation if the patient does not have a known cause.
The pharmacy conversation
When a patient presents with a discoloured nail, a brief structured assessment helps:
- How long has it been there? Acute = likely trauma. Chronic = likely fungal or other.
- Is it changing? Stable or growing out = reassuring. Widening or darkening = concerning.
- How many nails? Single nail = consider melanonychia referral. Multiple nails = fungal infection or psoriasis more likely.
- Any history of trauma? Direct question — patients often forget minor injuries.
- Any skin conditions? Athlete's foot, psoriasis, eczema may explain nail changes.
PharmSee's pharmacy finder can help patients locate pharmacies with experienced teams for skin and nail consultations. For pharmacy professionals, the salary guide tracks remuneration across clinical and community settings.
Key points
- Most nail discolouration is fungal infection or trauma — both manageable at the pharmacy counter
- OTC amorolfine nail lacquer is appropriate for mild-to-moderate fungal nail infections
- A single, new, widening dark longitudinal streak needs urgent dermatology referral (possible melanoma)
- Green nails suggest Pseudomonas infection — refer to GP
- Pitting, onycholysis, and oil-drop changes suggest psoriasis — refer for assessment
Sources: NICE CKS (Fungal nail infection), NHS (Nail problems), BAD (Nail disorders patient information). Article reflects guidance current as of April 2026.