This all sounds very promising, but it's a bit too soon to throw away your sunless tanner. The researchers have only tested these proteins out in skin cells in a lab, not in real people. They will need many further studies to figure out what effect this can have on body function as a whole. In the paper, the researchers note that its use would require careful considerations of safety. While they know that creating darker pigmentation is associated with the lowest risk of most skin cancers in humans, the SIK proteins work by inducing something called the MITF, which is the master regulator of pigment genes. They say that mutating or amplifying the MITF gene can cause cancer in certain contexts. While this process is not likely to trigger any mutations, it's impossible to know for sure without further studies. So far, in mice studies, they haven't found any increased carcinogenic risk.