There are no well-designed, evidence-based studies to answer the question, “Is spray tanning safe while breastfeeding?”
The general consensus is that spray tans are "probably safe." The active ingredient in the spray tan is a chemical called DHA that has been around for years. There are no studies that measure the levels of this chemical in breast milk, though, so scientists cannot say for sure. If you do decide to go this route, be sure to wash your breasts well before feeding your little one.
A tanning bed will not alter your breast milk so it is safe for your baby. However, doctors advise against tanning beds for your own protection because they give off UV rays, which cause not only sunburns but also skin cancer. If you do decide to go to a tanning bed, be sure to cover your nipples so they don't burn, or breastfeeding will be extremely painful!