Most scalp complaints are not infections. Itch, flaking, oiliness and tenderness usually trace back to seborrhoeic dermatitis, psoriasis, contact reactions or simple irritation. True infection is less common, and most cases fall into three families: fungal, bacterial, and viral.
The reason this matters is that the three families look different, behave differently, and need different treatment. Confusing one for another wastes time and sometimes makes things worse.
Fungal: tinea capitis and kerion
Tinea capitis is a fungal infection of the scalp caused by dermatophytes — most often Trichophyton and Microsporum species.1 It is predominantly a disease of children. Classic features are patchy hair loss with scale, broken hairs at the surface (“black dots”), and sometimes lymph nodes at the back of the neck.1
A kerion is the inflammatory form: a boggy, tender, pus-studded plaque that can be mistaken for a bacterial abscess.2 The pus is part of the immune response to the fungus, not a separate bacterial problem, and incising it does not help.
The point worth keeping is this: topical antifungal shampoos alone do not cure tinea capitis. Oral antifungal treatment is required, typically griseofulvin or terbinafine, for several weeks.3 Shampoos help reduce shedding of spores to household contacts but they do not reach the hair shaft itself.3
Bacterial: folliculitis, furuncles and impetigo
Bacterial scalp infections most commonly involve Staphylococcus aureus.4 Superficial folliculitis presents as small, tender, pus-tipped bumps around individual hair follicles. A furuncle (boil) is a deeper, more painful nodule. Impetigo, more common in children, shows honey-coloured crusts.5
Most superficial bacterial infections of the scalp respond to topical antibiotics and gentle cleansing.4 Deeper or recurrent infection, fever, or spreading redness warrants oral antibiotics and clinical assessment, particularly given the rise of methicillin-resistant strains.6
Two scalp-specific conditions deserve naming. Folliculitis decalvans is a chronic, scarring form of folliculitis that progressively destroys follicles and leaves smooth patches of permanent hair loss.7 Dissecting cellulitis of the scalp produces deep, interconnected nodules and sinus tracts, more common in young men, and is poorly responsive to simple antibiotics.8 Both are scarring, both need specialist care, and neither resolves with over-the-counter measures.
Viral: herpes simplex and herpes zoster
Viral infections of the scalp are uncommon but worth recognising. Herpes simplex can occur on the scalp, presenting as grouped vesicles on a red base, often painful or tingling before the rash appears.9
Herpes zoster (shingles) involving the scalp follows a nerve distribution, usually one-sided, with pain that may precede the rash by days.10 Early antiviral treatment within 72 hours of rash onset reduces severity and the risk of post-herpetic neuralgia.10 Anyone with a painful, one-sided scalp rash should see a clinician promptly.
What is not an infection
Several common scalp conditions are routinely mistaken for infection. Seborrhoeic dermatitis produces flaking and itch that can mimic mild tinea, but the underlying mechanism is an inflammatory response to commensal Malassezia yeast, not infection.11 Psoriasis causes thicker, silvery scale on well-defined plaques. Contact dermatitis from a new product produces redness and itch without pustules or broken hairs.
The practical signal that something is infectious rather than inflammatory: localised pus, tender swelling, fever, lymph nodes, or a rash that follows a nerve line. Diffuse flaking and itch across the whole scalp, without these features, is almost never infection.12
When to see a clinician
See a clinician for: patchy hair loss with scale in a child; a boggy or pus-filled scalp lump; honey-coloured crusts; a painful one-sided rash; fever with scalp tenderness; or any scalp problem that is worsening despite reasonable care. Scarring conditions, in particular, are time-sensitive. Treatment started early preserves follicles; treatment started late does not bring them back.
Most scalp complaints are not infections, but the ones that are deserve to be named correctly and treated promptly. Guesswork at home is fine for flaking. It is not fine for pus, pain, or hair coming out in patches.