No evidence exists that the use of tanning beds has any effect on human milk or breastfed babies. However some mothers have reported getting burnt nipples and breasts when using tanning beds: this is extremely painful so be sure to cover your nipples and breasts and use caution. If you are offered any vitamins or medications to enhance the tanning process you can check them with your health care provider before taking them.
You do not need to avoid using tanning lotion, or having a spray tan, when you’re breastfeeding. You do however need to take care when applying fake tan (or indeed any cosmetics) when your baby is close, and you need to ensure the fake tan is dry or has been rinsed off before having skin-to-skin contact to avoid accidentally ‘tanning’ your baby.
The active ingredient in most fake tans is DHA, and some self tanners use erythrulose. Both are non toxic: neither substance can absorb beyond the outermost layer of your skin, and so cannot contaminate your breast milk or harm your baby.