Synopsis
Recognise the herald-patch and cleavage-line eruption, identify pregnancy and diagnostic exceptions, exclude tinea or secondary syphilis when indicated, and avoid overtreating a self-limiting rash.
- Pityriasis rosea often starts with one 2 to 5 cm scaly herald patch on trunk or proximal limb, followed days to two weeks later by many smaller oval scaly lesions.
- Secondary lesions align with cleavage lines, forming a fir-tree distribution across the back; a herald patch is helpful but not present or recognised in every case.
- On brown or black skin, lesions may be deep brown or have a lighter border rather than look pink, and post-inflammatory lighter or darker marks may last for months.
- Palms, soles, face and mucosae are usually spared; involvement there, systemic illness, drug timing or sexual risk should redirect the differential.
- Diagnosis is clinical when the sequence is typical. Scrape a solitary annular herald-like patch for fungus when uncertain, and use syphilis serology when history or distribution supports it.
- Most eruptions resolve in six to eight weeks or within a few months, need no specific treatment and do not require school exclusion.
- For discomfort, use fragrance-free emollient or soap substitute, an appropriate antihistamine, and prescribed mild topical corticosteroid; BAD describes hydrocortisone ointment twice daily for troublesome itch.
- Any new rash during pregnancy needs immediate maternity, GP or NHS 111 contact, especially in the first 15 weeks.
Key red flags
Pregnancy with a new pityriasis-rosea-like rash needs immediate maternity or clinical assessment because early-pregnancy disease has been linked with miscarriage and preterm birth.
Palmar or plantar lesions, mucosal patches, lymphadenopathy, neurological symptoms or sexual risk should prompt testing for secondary syphilis and other systemic mimics.
Skin pain, dusky targets, blisters, mucosal erosions, facial oedema or systemic organ symptoms suggests a severe drug reaction rather than uncomplicated pityriasis rosea.
Persistence beyond three months, marked constitutional illness, ulceration or progressive atypical morphology warrants diagnosis review and possible dermatology assessment.
A new rash in pregnancy must not be self-labelled. NHS advises immediate contact with maternity care, GP or NHS 111 because early-pregnancy pityriasis rosea has reported adverse associations.
Palms, soles, mucosae, prominent face involvement, vesicles, purpura, pain or lesions persisting beyond the expected course should trigger targeted investigation or referral.
Investigation priorities
Confirm a herald lesion followed by cleavage-line secondary eruption and identify atypical palms, soles or mucosae.
Management branches
Classic herald sequence and cleavage-line rash in a well, non-pregnant person without atypical sites.
- Explain that the eruption is not usually contagious, often peaks before improving, and commonly settles in six to eight weeks or within a few months without scar.
- No active treatment is needed if comfortable; continue school, work and ordinary contact, and avoid irritant soap or unnecessary antimicrobial treatment.
- For itch, use fragrance-free emollient or soap substitute and an appropriate antihistamine; add a short mild topical corticosteroid course if symptoms remain troublesome.
- Advise review if the rash has not resolved by three months, becomes painful or blistered, involves mucosae, palms or soles, or systemic symptoms develop.