Sarina is 26 years old and attends the GP due to a rash which has spread over her back. She first noticed it yesterday and says it is slightly itchy. She feels well in herself but admits that last week she had coryzal symptoms and got back from Spain 10 days ago from a family holiday.

She has no new skin products or medications and has no dermatological history apart from childhood eczema.

On examination she is apyrexial and you note a widespread symmetrical maculopapular rash with collarette scaling.

What is her most likely diagnosis?