“It started with one big patch and now it’s all over my chest and back — is it catching?”

Pityriasis rosea typically starts with a single larger oval, scaly “herald patch”, followed days to weeks later by smaller oval patches on the trunk and proximal limbs along skin cleavage lines (the “Christmas tree” pattern), often after a viral-type prodrome. It is self-limiting, usually clearing within 6–12 weeks, has low infectivity and needs no exclusion. The key differential is secondary syphilis, which can look almost identical: look for palm and sole involvement, mouth ulcers, genital ulcers, patchy hair loss and lymphadenopathy, and take a sexual history; arrange syphilis serology where there is any doubt or risk, and offer a full STI screen. Pregnancy changes management. Pityriasis rosea in pregnancy, particularly in the first 15 weeks, has been associated with miscarriage in some case series; NICE CKS advises seeking specialist advice for pregnant women. The doctor needs to give this information honestly without catastrophising, inform the midwife or early pregnancy team, and not delay syphilis testing until booking bloods (untreated syphilis in pregnancy risks congenital syphilis, and antenatal screening is offered to all pregnant women). Itch can be managed with emollients and, if needed, a mild or moderate topical corticosteroid (check the SPC/local formulary). The communication task is a sensitive sexual history, a non-judgemental response to disclosure, confidentiality about previous partners, and partner notification only if a result is positive (BASHH guidance).