This is an easy question to answer... Simply use soap and water!
It is VERY IMPORTANT to never use any chemical cleaners such as Cillit Bang, Flash or the one that loves the jobs you hate. If incorrect shower cleaners are used, they will affect your paint/chrome/metal finishes. They will burn and bubble the paint and this is most commonly seen around the water control knobs, around light recesses... in fact, any recess. Why? Because the chemical will be very hard to remove in these areas with a hand shower or cloth and the surface starts to gradually build up with chemical acids that will cause bubbling as seen with paint strippers. There is no other cause for this as the panel is aluminium, therefore if this happens, this would not be covered by our warranty as it's not a manufacturing defect!