Honestly mama, I haven't used kojic acid myself while breastfeeding kasi I was worried din, but a few of us in my mum group said it should be okay since it's mostly topical and hindi siya absorbed much into your bloodstream, pero iba-iba talaga ang katawan, so better safe than sorry and check with your OB or dermatologist na first para sure, especially since you're putting it on exposed skin na malapit sa baby sometimes. Better peace of mind, di ba?