It's only unhealthy when the (1) the sun is out (no clouds), (2) the "shadows are short" (sun over 45° angle), (2) there's no (semi-)cover, and (3) you are in t

It's only unhealthy when the (1) the sun is out (no clouds), (2) the "shadows are short" (sun over 45° angle), (2) there's no (semi-)cover, and (3) you are in there already over ~15min for that day (this is different per skin type and tan-level). Below that it's very healthy.