I was reading up on this because I want to spray tan also. I read that as long as you wash your nipples and stuff off afterwards, it should be OK. I'll try and dig for the article. And it shouldn't affect breastmilk or anything like that.
Can't find the original but here is something similar to what I read:
However before I get into all of that YES it is safe as so very little is absorbed into your blood. Just -obviously- wash your nipples off after the application before breastfeeding.
(ok yahoo is hating my links again.... so I've taken them out)
[ link to k e l l y m o m . c o m ]
Sunscreen, Self-tanning products
Because these are topically applied, very little would absorb through the skin into the bloodstream and therefore into your milk. They should not be a problem for the breastfeeding mom and baby. Do be careful about applying it on the breast - make sure baby doesn't get any in his mouth.
The spray tanning booths (also called UV-free tanning, airbrush tanning, spray on tanning, etc.) come under the category of self-tanning products. To prevent baby ingesting the self-tanning lotion, wash the self-tanning product from your breasts before nursing.
[link to p a r e n t i n g . i v i l l a g e . c o m ]
Self-tanning preparations are increasing in popularity. They're a great way for you to get a tanned look, without the risks of overexposure to the sun.
The active ingredient in self-tanning products is dihydroxyacetone (DHA). It is derived from sugar cane. This reacts with the amino acids in the upper layers of the skin to produce a tan. No dyes are used, and this is considered to be a safe process.
In general, there is some absorption from any product used on the skin. Only use if your skin is not damaged. There is no evidence that use of skin care products has any negative effect on your nursing baby. When applying to the breast, avoid using around your areola and nipple. Allow to dry thoroughly (about one hour) before breastfeeding.