DermNet

The authoritative resource about dermatology and the skin: dermnetnz.org The world's most popular skin website - written and edited by Dermatologists worldwide.

23/09/2026

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

20/09/2026

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

16/09/2026

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?

09/09/2026

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

06/09/2026

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

02/09/2026

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

30/08/2026

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

26/08/2026

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?

23/08/2026

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

19/08/2026

Jessner lymphocytic infiltrate can look strikingly similar to tumid lupus erythematosus — both present as smooth, non-scaly red plaques on sun-exposed skin. For years the two were considered part of the same disease spectrum, until immunostaining (Leu 8) suggested they may in fact be distinct conditions. The cause remains unknown, though rare cases have been linked to Borrelia infection and certain medications, including duloxetine and ustekinumab. Most cases resolve spontaneously without scarring, sometimes after months or years.

Read more here: https://dermnetnz.org/topics/jessner-lymphocytic-infiltrate

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