It may be winter in the southern hemisphere, but in the northern hemisphere the nano-sunscreen safety debate has been heating up. Following a challenge from Andrew Maynard on his 2020 Science blog to specify a worst case scenario health outcome from using nano-sunscreens, Friends of the Earth Australia and United States responded. The subsequent debate is ongoing. Do you think regulators should carry out safety assessment on nano-sunscreens before they can be sold? Do you think nano-ingredients should be labelled? Why not have your say?