I am formulating the bleaching creams in my clinic.I use the following formula
Hydroquine 3%
kojic 3%
ascorby palmitate 3%
lactic acid 2%
vitamin E 1%
retine A 0.01%
azelaic acid 4%
vitamin k 2%
Hydrocortison 2%
My quositon is normaly I put methyl paraben and propyl paraben as a preservave.Tetra sodium EDTA as chelator and as well as lactic acid anti bacterial.when it kept in refragarator it will not change its color but out side refragator within one week it change its color and please advice me to maintain its stability.

This looks like it will be effective in lightening. Parabens are carcinogenic and can cause cancer and EDTA is cytotoxic and an organic pollutant (I'm trying to search for safer options in cosmetics). Grapefruit Seed Extract, Potassium Sorbate are among the few known to be safer options. Also, hydrocortisone is a steroid, are you sure you want to use it in your formula? How long will your formula last in the refrigerator?

Abdella can you post the directions on how to mix the ingredients or pm it to me?

Edit: I had to erase the Germaben II because I read that it is parabens.