Exposure to UV radiation—at any level—has the potential to damage your skin. But that potential is much greater at higher levels of UV radiation.
Doctors say the safest way to get a tan is to gradually expose your skin to the sun for limited durations at UV levels under 3.
For more on the topic of tanning, see our in-depth article on the best UV index for tanning. We cover the effects of solar UV radiation at different time intervals and index levels.