In people

What people notice first is colour, and it arrives slowly. In the original Arizona work, ten doses over twelve days produced measurable darkening of the forehead, arms and neck that peaked one to three weeks after the last dose and was still visible three weeks later, with no change at all in those given saline. People with pale, poorly tanning skin darkened as well as good tanners did, which surprised the researchers at the time. With the specialist implant, people with light-intolerant skin report usable hours outdoors for the first time, and that is measured in how much pain-free light exposure they get. Reported effects are mild: occasional stomach upset, facial flushing, sometimes a headache or a tired feeling in the first day or two. The colour is even rather than patchy, it fades over one to two months as pigmented skin cells are shed, and it is a real tan in the sense that it is your own eumelanin, made by your own cells. Dermatologists in Europe have also documented what happens with loose unregulated powder: existing moles darkening, new irregular moles appearing, and a handful of melanomas reported in or near moles during or shortly after use, which is why the people who work with this molecule map and photograph moles before anything starts.