Competitive inhibition of actives in a lightening skincare range
I have a manufacturer creating a lightening skincare range for me (day, night cream, serum, dark spot corrector). Feedback from initial samples was that none of the testers noticed any lightening/brightening/radiance effect from the products. No objective data was collected but subjectively if no change was noticed even after 2 months of use then repeat sales of the product would be unlikely. After lengthy discussion with the cosmetic chemist on how to improve the effectiveness of the formulations, it was suggested that we have too many actives per product (4 actives) and that there was a chance they were competitively inhibiting the action of each other. They felt a simpler formula with 2 actives and at higher concentrations would produce better results.
I wanted to get feedback as to whether their suggestion sounds the best or whether they should be able to identify any interactions between actives and therefore maybe they do not have enough knowledge in this area?
Any thoughts/comments welcome.