Scalp itch is common in people of all ages. Treatment depends on an accurate diagnosis. Causes range from everyday skin conditions such as seborrhoeic dermatitis, psoriasis and head lice to rare disorders such as dermatitis herpetiformis and trigeminal trophic syndrome.
- Scalp pruritus is a feature of many common dermatological conditions, including seborrhoeic dermatitis, psoriasis, pediculosis capitis, atopic dermatitis or eczema, lichen simplex chronicus and contact dermatitis.
- Scalp pruritus may also be a prominent feature of rare conditions such as dermatitis herpetiformis, lichen planopilaris and trigeminal trophic syndrome.
- Pruritus of the scalp can occur without any discernible skin changes; psychological issues can exacerbate or manifest as scalp pruritus.
- Scalp pruritus can be a diagnostic and therapeutic challenge; distinguishing features in the patient’s history should be sought and physical examination should include whole-body skin inspection.
- Sometimes a therapeutic trial is required before the diagnosis is established.
- A definitive cause for scalp pruritus is not always found; these patients may benefit from symptomatic antipruritic treatments.
- Referral to a dermatologist is recommended when the diagnosis remains unclear or the disease does not respond to treatment. Early dermatology referral is essential for patients with dermatitis herpetiformis, lichen planopilaris and alopecia.
Scalp pruritus is a frequent presentation to GPs. This article outlines the clinical features and treatment of common dermatological conditions associated with scalp pruritus, as well as some rare but important causes of this condition. A summary of the common causes of scalp pruritis is listed in Table 1; a summary of less common causes of scalp pruritus are listed in Table 2 & 2b.
Common causes of scalp pruritus
Seborrhoeic dermatitis is a common dermatosis with a predilection for sites of increased sebum production, including the scalp, ears, face, central chest and major body folds (Figures 1a and b). Although the cause of seborrhoeic dermatitis remains unknown, the commensal yeast Malassezia furfur has been implicated in its pathogenesis.
Infantile and adult forms are distinguishable. The infantile form, commonly known as ‘cradle cap’, occurs in the first three months of life and is self-limiting. The adult form tends to begin in late adolescence and persist into adulthood, with peak prevalence in the third and fourth decades.
Seborrhoeic dermatitis has an estimated prevalence of 3% in the general population. For reasons that are not completely understood, seborrhoeic dermatitis is more common in individuals with HIV infection and neurological disorders, notably Parkinson’s disease. Indeed, severe or recalcitrant seborrhoeic dermatitis may be the presenting sign in patients with HIV infection.
In its mildest form, seborrhoeic dermatitis of the scalp is referred to as dandruff (also called pityriasis capitis), and is characterised by diffuse, fine white scaling without inflammation. With more extensive disease, greasy yellow to salmon- coloured scales overlay patches of inflamed skin (Figure 1a). Areas of affected skin may be asymptomatic or extremely itchy. Seborrhoeic dermatitis can mimic psoriasis but, in the latter, plaques are well demarcated, thicker and more inflamed (Figures 2a and b). The presence of nail changes and plaques elsewhere on the body in psoriasis can help differentiate it from seborrhoeic dermatitis (Figure 2c).