DermNet

Despite its name, pyogenic granuloma has nothing to do with pus or infection and is a benign proliferation of capillary blood vessels, essentially a reactive haemangioma. It grows rapidly over days to weeks, often after minor trauma, and bleeds easily even with light contact. In pregnancy it's sometimes called a "pregnancy tumour," resolving after delivery in many cases but outside pregnancy, recurrence is common unless the underlying trigger (trauma, certain medications, hormonal factors) is addressed.

Read more here: https://dermnetnz.org/topics/pyogenic-granuloma

Roseola has a distinctive and often confusing pattern: a high fever for 3–5 days, then, just as the fever breaks and the child seems to be improving, a pink, blanching rash appears on the trunk. It's caused by human herpesvirus 6B (and possibly HHV-7), and by age one, most children have already had it. Febrile seizures occur in 5–15% of cases due to the high temperatures, but they're brief and not dangerous. No specific treatment is needed as the rash itself is painless, non-itchy, and resolves on its own.

Read more here: https://dermnetnz.org/topics/roseola

Onychophagia also known as nail biting is often dismissed as a harmless habit, but it can have real physical consequences beyond the nail itself: paronychia, fungal nail infection, and even teeth root resorption and malocclusion from chronic biting. It's classified as a form of onychotillomania and is associated with (though doesn't necessarily indicate) conditions such as OCD, ADHD, and anxiety disorders. Children can outgrow it, but persistent or severe cases benefit from behavioural treatment addressing the habit at its root.

Read more here: https://dermnetnz.org/topics/onychophagia

A 33-year-old woman presented with a five-year history of pink, scaly papules and erythema around the nasolabial folds, chin, and upper lip, exacerbated by heat and stress.

What could this be?

Blackheads dark colour comes from melanin, not trapped grime, which is why scrubbing harder doesn't clear them. They can either be closed or opened. Comedonal acne develops when skin cells lining the follicle proliferate and sebum production increases, blocking the duct with debris. Certain habits can make it worse, including oily cosmetics, smoking, and squeezing or picking at spots, which can rupture the follicle and worsen inflammation. Effective treatment relies on comedolytic agents like retinoids, benzoyl peroxide, or azelaic acid used consistently over weeks to months.

Read more here: https://dermnetnz.org/topics/comedonal-acne

Erosive pustular dermatosis of the scalp — clinical features, associations, and management. Swipe to learn more or check out our full DermNet page on: dermnetnz.org/topics/erosive-pustular-dermatosis

A digital myxoid pseudocyst isn't a true cyst as it has no capsule lining it, hence the name. It typically appears near the base of a fingernail, often pressing a visible groove into the nail plate. One key driver: many arise from the joint lining itself, as a form of ganglion linked to underlying osteoarthritis of the distal finger joint which helps explain why they're so notoriously prone to recurrence, whatever treatment is used.

Read more here: https://dermnetnz.org/topics/digital-myxoid-pseudocyst

Erythema annulare centrifugum is best known for one distinctive clue: a delicate "trailing scale" just behind its slowly advancing, ring-shaped border. But the real diagnostic value lies in what's driving it - in up to 72% of cases, EAC is a reactive marker for an underlying trigger, most often a fungal infection like tinea pedis, but sometimes malignancy, medications, pregnancy, or endocrine disease. This is why identifying and treating the underlying cause, rather than just the rash, is central to management.

Read more here: https://dermnetnz.org/topics/erythema-annulare-centrifugum

A 40-year-old man presented with three recurrent episodes of target-like lesions affecting the palms and soles over three months. What are your differentials for this?

Knuckle pads are frequently assumed to be a callus from a repetitive habit - and sometimes they are, linked to occupational or sporting friction, or even finger sucking or biting. But true knuckle pads belong to the same family as Dupuytren contracture and Ledderhose syndrome: fibromatosis. They typically appear after age 30, can run in families, and occasionally form part of a genetic syndrome and most notably alongside keratin gene mutations in epidermolytic palmoplantar keratoderma. On ultrasound, they're distinguishable from joint synovitis, which can otherwise mimic their appearance.

Read more here: https://dermnetnz.org/topics/knuckle-pads