Nail Infection – Consultant Diagnosis & Treatment for Fungal, Bacterial or Viral Nail Disease in London

Understanding nail infection

Nail infection describes any microbial invasion of the nail unit. The commonest is fungal infection of the nail plate (onychomycosis), but infections can also involve the surrounding skin (paronychia), the space beneath the nail (subungual infection), or specialised structures like the matrix. Distinguishing infection from look‑alike conditions (psoriasis, eczema, trauma, melanonychia) is critical because the treatments differ completely.

Toenails are more often affected than fingernails due to warm, moist footwear and slower growth. Fingernail infections frequently follow wet‑work, manicures, gel/acrylic cycles, nail biting or thumb‑sucking, and minor injuries.

Types and causes of nail infection

• Fungal infection (onychomycosis) — dermatophytes (e.g., Trichophyton rubrum) are most common; yeasts (Candida) and moulds sometimes contribute. Hallmarks are yellow/white discoloration, thickening and crumbly edges, often starting at the free edge and spreading proximally. Toenails frequently coexist with athlete’s foot.
• Acute bacterial paronychia — sudden, painful swelling and pus at the nail fold after a hangnail, nail biting or manicure; typically due to Staphylococcus aureus or streptococci.
• Chronic paronychia — persistent inflamed, tender nail folds in people with wet‑work or irritant exposure; often a mixed picture of irritant dermatitis, Candida colonisation and bacteria.
• Pseudomonas “green nail” — green/black discolouration under a partially detached nail due to colonisation with Pseudomonas aeruginosa, favoured by moisture and occlusion.
• Viral nail infections — periungual warts (HPV) distort the nail edge; herpetic whitlow (HSV) causes painful grouped blisters around the fingertip and nail fold and must not be incised.

Risk factors

• Untreated tinea pedis (athlete’s foot) acting as a fungal reservoir.
• Wet‑work (hospitality, cleaning, hairdressing) and frequent water/chemical exposure.
• Tight footwear, repetitive trauma, long‑distance running.
• Diabetes, peripheral vascular disease, neuropathy.
• Eczema/psoriasis affecting the hands and nail folds.
• Immunosuppression (medication or illness).
• Nail salons with poor instrument hygiene or aggressive cuticle cutting.
• Smoking and poor foot hygiene.

Symptoms and signs

• Onychomycosis: yellow, white or brown discolouration; thickened or brittle nail; debris under the nail; onycholysis (lifting) and odour; multiple toenails may be involved.
• Acute paronychia: red, hot, swollen nail fold; throbbing pain; visible pus; worsens on pressure; sometimes systemic symptoms if severe.
• Chronic paronychia: mildly swollen, tender, ragged cuticles; recurrent flares; transverse ridges and nail plate irregularity over time.
• Green nail: bright green to black staining beneath a lifted nail; usually painless but cosmetically striking; may accompany onychomycosis.
• Herpetic whitlow: tingling, burning pain then grouped vesicles; very tender; regional lymph nodes may swell.
• Periungual warts: rough papules encroaching on the nail; may cause pain and deformation.

Diagnosis

Accurate diagnosis avoids unnecessary or prolonged treatment. At Skinhorizon, we follow an evidence‑based pathway:

• Onychoscopy (dermoscopy of nails): distinguishes fungal patterns and evaluates pigment bands.
• Mycology: nail clippings/scrapings for microscopy and culture, or PAS stain of nail plate to confirm fungus before oral antifungal therapy.
• Bacterial culture: swabs or aspirate in acute/chronic paronychia or green nail.
• Viral diagnosis: clinical for warts; PCR swab if whitlow is uncertain.
• Imaging: ultrasound/MRI when a deep abscess or tumour is suspected.
• Biopsy: nail matrix/bed biopsy when tumours, lichen planus, or atypical melanonychia are in the differential.

Treatment and management

Therapy is tailored to the organism, severity and patient factors (age, pregnancy, comorbidities). Nails grow slowly; visible improvement reflects new growth from the matrix and may take months.

Fungal nail infection (onychomycosis)

• Topical antifungals: amorolfine or ciclopirox lacquers for mild/distal disease or when oral drugs are unsuitable. Apply regularly for 6–12 months; file the nail surface weekly to enhance penetration.
• Oral antifungals: terbinafine (dermatophytes) or itraconazole (pulse therapy) for extensive, multiple or matrix‑involved disease. Baseline interactions and, in some cases, liver tests are considered. Treat concurrent athlete’s foot to prevent reinfection.
• Adjunctive care: debridement/thinning of thick nails, disinfect footwear/socks, keep feet dry, rotate shoes, use antifungal powders.

Acute bacterial paronychia

• Early cases: warm saline soaks, elevation, topical antiseptics; short course of appropriate oral antibiotics if spreading or severe, tailored to local guidance and culture.
• Abscess: sterile incision and drainage under local anaesthetic. Culture pus; give antibiotics if cellulitis or high‑risk patient.
• Pain control: simple analgesia; avoid further trauma and moisture.

Chronic paronychia

• Barrier restoration: minimise wet‑work; cotton liners under waterproof gloves; avoid irritants and cuticle cutting.
• Topicals: combination of mild‑to‑moderate topical corticosteroids plus antifungal (e.g., azole) to break the cycle of inflammation/yeast colonisation.
• Refractory cases: short courses of calcineurin inhibitors or, rarely, surgical eponychial marsupialisation.

Pseudomonas “green nail”

• Mechanical care: debride detached nail; keep the area dry and aired.
• Topicals: antiseptic soaks (e.g., dilute acetic solution as guided) or topical antibiotics as clinically appropriate; treat coexistent onychomycosis.
• Avoid occlusion: limit gel/acrylics until the plate reattaches and colour clears.

Viral infections

• Periungual warts: cryotherapy, salicylic acid, curettage or laser depending on size and pain; patience is key as recurrence is common.
• Herpetic whitlow: Do not incise. Early oral antivirals may shorten the course; keep covered, avoid contact spread (especially to eyes), and manage pain.

Prevention and self‑care

• Treat athlete’s foot to stop reseeding toenails.
• Keep nails short and dry; change socks daily; use moisture‑wicking fabrics.
• Choose roomy shoes; rotate pairs to allow drying; disinfect footwear during antifungal therapy.
• For hands, reduce wet‑work; wear cotton liners under nitrile gloves; moisturise nail folds with bland emollients.
• Avoid cuticle cutting and aggressive manicuring; insist on proper salon sterilisation; consider breaks from gel/acrylics.
• Do not share nail clippers or files; clean tools with appropriate disinfectants.
• Maintain good glycaemic control in diabetes and see a clinician early if redness or pain develops.

Special groups

• Children: infections are often minor; confirm diagnosis before prolonged treatment. Periungual warts are common and may resolve spontaneously.
• Pregnancy: topical therapies are preferred; many systemic antifungals are avoided—seek specialist advice.
• Immunosuppressed patients: atypical and extensive infections occur; lower threshold for cultures, biopsy and systemic therapy.
• Diabetes/vascular disease: higher risk of cellulitis and ulceration; early treatment and podiatry input reduce complications.

When to seek urgent help

• Severe pain, rapidly spreading redness or fever (possible cellulitis/abscess).
• A new, irregular, widening dark band on one nail, especially with pigment on surrounding skin (possible subungual melanoma—urgent assessment).
• Failure of appropriate treatment or recurrent infections impacting work, sport or mobility.

Prognosis

Most nail infections respond well to targeted therapy plus practical nail‑care changes. Because nails grow slowly, full cosmetic recovery may take 4–6 months for fingernails and 9–12 months for toenails. Preventing reinfection—especially by treating athlete’s foot, improving footwear and reducing wet‑work—is essential to long‑term success.

Your first visit — what to expect

1. History: onset, symptoms, prior treatments, trauma, salon/occupational exposure, medical conditions and medications.
2. Examination: onychoscopy of affected nails and surrounding skin; assessment for athlete’s foot.
3. Investigations: nail clippings/scrapings for microscopy/culture or PAS; swabs/cultures for paronychia; consider biopsy if diagnosis is uncertain.
4. Management plan: tailored therapy (topical/oral, procedures), footwear and hygiene advice, plus strategies to prevent recurrence.
5. Follow‑up: review to confirm pathogen eradication and healthy regrowth; adjust treatment if needed.

Reviewed by: Dr Mohammad Ghazavi, Consultant Dermatologist
Skinhorizon Clinic, 4 Clarendon Terrace, Maida Vale, London W9 1BZ
Last reviewed: 22 August 2025