Thanks greentea, I had a look on the paper you provided. The majority of research findings focused on the effect of overdosage and reaching the maximum concentration of Vita A in the body, which to me only provide a little light to my questions. If I draw the focus on cosmetic application, extracted below are the key findings to me:
1. "In human studies, there is no evidence that topically applied retinol or retinoid metabolites induce detectable changes in their constitutive plasma levels"; "no significant increase in plasma levels of retinoids could be detected after repeated applications of retinal, retinol or retinyl palmitate";
2. Dermal absorption is limited.
3. The paper took on an assumption and conducted studies: Face cream vita A concentration 0.3%; Absorption ofretinol from topical products is 7.7 %; Estimated absorption rates in the range of 5-8%;
Talking about lactation specially, the paper discussed their concerns on overdosage of Vit.A, which may lead to bone fractures (over 1500ug/day) (however not robust enough to have positive conclusion).
Hence, I am not dare to make assumption that based on the above extracted findings no.1-3, application of Vita A face cream (0.3%) is free and safe during lactation as it depends your overall consumption of Vita orally too. Any comments or other interpretation? Thanks!