Is it bad to spray tan over a spray tan?

In general, it’s not the best idea.  Spray tanning solution is drying to the skin.  Spray tanning on top of another airbrush tan will dry out the skin to the point where the new tan may not fully develop well.  Especially in climates in the midwest with harsh winters and dry skin most of the year.  It can cause patchiness, poor fading, and poor coloring.  Typically, you want to wait until the first spray tan has faded before getting another one.  And if you use choose to tan over a previous tan, it is strongly suggested to add CBD or a Moisturizing Treatment to help the fading process.