Dermatology

A bacterial infection (Kytococcus sedentarius and related species) causing malodorous, punched-out pits on the sole, associated with hyperhidrosis and occlusive footwear. Treat with a topical antibiotic — mupirocin, clindamycin or fusidic acid — alongside moisture control (antiperspirants, breathable footwear, moisture-wicking socks).

A dermoid cyst is a mature (benign) teratoma — a congenital cyst containing tissue from multiple germ layers (skin appendages, hair, sebaceous material, occasionally teeth or cartilage), typically found along embryonic fusion lines such as the lateral eyebrow, midline nose, or scalp.

Often polymicrobial: Candida albicans (isolated in around 93% of cases) and Staphylococcus aureus (around 20%) frequently coexist, alongside Streptococcus species.

• Risk factors: type 2 diabetes, immunocompromise, older age, ill-fitting dentures, nutritional deficiency (iron, B12, folate, riboflavin), and a lip-licking/drooling habit that keeps the skin folds chronically moist.

Dome-shaped, umbilicated papules with a pearly, rounded edge — classically across the trunk. Spread is by direct skin contact (including sexual contact in adults); in children, genital lesions are usually from autoinoculation/spread from other body sites rather than a marker of abuse, though the possibility should still be considered appropriately in context.

Self-limiting in immunocompetent patients — most resolve within 6–18 months without treatment, so deroofing/curettage isn't routinely needed. Active treatment is reserved for persistent, cosmetically bothersome, or immunocompromised cases.

Corynebacterium minutissimum infection causing well-demarcated red-brown patches in skin folds (groin, axillae, toe webs) — fluoresces coral-pink under Wood's lamp (coproporphyrin III), a quick bedside way to distinguish it from tinea.

Treatment: topical fusidic acid first-line, oral or topical erythromycin second-line (or for more widespread disease).

Also called perifolliculitis capitis abscedens et suffodiens — part of the follicular occlusion tetrad alongside hidradenitis suppurativa, acne conglobata and pilonidal disease. Painful nodules with interconnecting sinus tracts and purulent discharge.

• Oral doxycycline (± rifampicin) for milder disease.
• Intralesional corticosteroid injections for inflammatory nodules.
• Oral isotretinoin where there's scarring, keloid formation or patchy alopecia.
• Biologics (e.g. adalimumab) are an emerging option for refractory disease.

Remove the trigger — classically topical corticosteroid use (even low-potency), and heavy/occlusive moisturisers or cosmetics — plus oral doxycycline for 6–12 weeks. Expect an initial flare after stopping steroids before it improves; topical metronidazole or erythromycin can be used for milder disease.

In males, the genital form is also called balanitis xerotica obliterans (BXO) — white, atrophic patches causing a tight foreskin that can't be fully retracted (phimosis), which can progress to urethral meatal stenosis and a deviated or spraying urinary stream. Circumcision is often required where phimosis is significant.

In females, lichen sclerosus classically causes itchy, atrophic white plaques in a "figure-of-8" distribution around the vulva and perianal skin, with a small increased long-term risk of vulval squamous cell carcinoma — worth long-term follow-up.

Small, "drop-like" papules over the trunk and proximal limbs, classically triggered by a preceding infection — usually streptococcal (e.g. tonsillitis). May resolve spontaneously over weeks to months, though a subset go on to develop chronic plaque psoriasis.

Usually absent or minimal at birth, appearing in the first few weeks of life, then growing rapidly through the first year (proliferative phase) before spontaneously regressing over the following years (involution) — this growth-then-regression pattern is what distinguishes it from a vascular malformation, which is present at birth and grows proportionately with the child without regressing.

Most need no treatment. Oral propranolol is first-line where treatment is indicated — ulceration, visual axis or airway compromise, or a cosmetically significant facial lesion.

Classic culprits: allopurinol, anticonvulsants (carbamazepine, lamotrigine, phenytoin), sulfonamides, and NSAIDs.

An autoimmune subepidermal blistering disease — typically older patients, intensely itchy, tense bullae on an erythematous/urticated base, mainly the trunk and proximal limbs. Mucous membranes are usually spared, and the bullae are tense (unlike pemphigus vulgaris, which more often involves mucosa and has flaccid, easily ruptured blisters) — a useful bedside differentiator.

A benign, self-limiting neonatal rash requiring no treatment beyond parental reassurance — typically appears within the first few days of life and resolves spontaneously within 1–2 weeks.