Philippa says a

Pityriasis versicolor is a fungal skin infection which commonly affects the chest and back. On fair-skinned people it looks like small, often oval, slightly darker patches, but on tanned skin, or those from an Asian or African background it can look like paler patches, which can also be reddish or pink in colour – hence the versicolor (means multi-coloured) part of the name. If the antifungal (body) shampoo doctors usually prescribe this hasn’t worked, try a shampoo containing selenium sulphide. Apply daily for seven days and leave on for 10 minutes before rinsing off. If it causes skin irritation, dilute it a little before applying. If that doesn’t ask your GP about treatments like antifungal cream or oral antifungal treatments. It can return again – for example when going away to a hot place – so you may wish to try the antifungal shampoo in advance.