GPAtlas🧭 When to suspect
Pityriasis rosea is an acute, self-limiting papulosquamous eruption, most likely caused by endogenous reactivation of human herpesvirus 6 and 7 (HHV-6/HHV-7). It is not contagious.
• Largely a disease of teenagers and young adults – most cases occur between 10 and 35 years
• A slight female excess and a recognised increase in pregnancy
The classic sequence:
• A single herald patch.
• 1–2 weeks later, a symmetrical eruption of smaller oval, scaly, pink patches across the trunk and proximal limbs.
• The patches align along the lines of cleavage to give the characteristic ‘Christmas tree’ pattern on the back.
Diagnosis is clinical.
The two jobs in primary care:
• Recognise the pattern and reassure
• Actively exclude its important mimic, secondary syphilis
While remembering the one group in whom pityriasis rosea is not a trivial diagnosis: pregnant women, particularly in the first 15 weeks.
| Key differential | How to distinguish |
|---|---|
| Secondary syphilis | • Palms and soles involved, mucosal lesions, generalised lymphadenopathy, sexual-health risk – the must-not-miss mimic • Check treponemal serology |
| Guttate psoriasis | Smaller ‘tear-drop’ scaly papules, often post-streptococcal, with scalp/extensor involvement and no herald patch. |
| Tinea corporis | • A single annular plaque with a leading scaly edge – the solitary herald patch is the classic mimic • Confirm with skin scrapings if unsure |
| Nummular (discoid) eczema | Coin-shaped, more eczematous and crusted, intensely itchy, with no ‘Christmas tree’ distribution. |
| Pityriasis versicolor | • Hypopigmented or hyperpigmented macules on the upper trunk • Malassezia hyphae and spores on microscopy |
| Drug-induced PR-like eruption | Often no herald patch, atypical distribution, and fails to clear until the responsible drug is withdrawn. |
|
⚠️ Common pitfall • Committing to a diagnosis on the solitary herald patch. • In isolation the herald patch is frequently mislabelled as tinea corporis or eczema and treated accordingly. • The diagnosis declares itself 1–2 weeks later when the symmetrical ‘daughter’ lesions erupt along the lines of cleavage. • Resist anchoring on a single annular patch. |
Source: DermNet · British Association of Dermatologists
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