The early bird gets the worm -- and may avoid skin cancer. Because a new mouse study that, for humans, tanning in the mornings may be less likely to permanently damage DNA and cause skin cancer. A mouse’s levels of the DNA-repairing protein XPA are different from ours -- they peak in the morning and bottom out in the evening. Researchers exposed mice to UV radiation when their XPA was at its minimum level, around 4 a.m., and others to the same rays around 4 p.m., when XPA levels peaked.