In general, I remove anything on the skin prior to laser treatments. The makeup itself won't cause a problem but it can interfere with the laser light, especially if the makeup is dark. As a rule, it's better not to wear makeup on an area you are going to have treated with a laser.
No, having the foundation on will most likely not impact your results. If however, your makeup clogs the pores and/or blocks the follicle to which the laser is to be targeting, it can prevent the successful removal by the laser. You should wait 4-6 weeks for the hair to go through all stages before having another treatment. Next time you have the laser, a fresh cleaned face is best.Thank you for your question and good luck!Melinda Lacerna, MD FACS