Hi topace.
Just be careful. It sounds like you are probably buying some generic products that are being unethically marketed as genuine Diana Stalder products. The reason I say this is because there is no genuine Diana Stalder product known as "Kojic acid cream" or "Glycolic cream." These are names of products typically used by sellers of the generic, unlabeled products.
Often these sellers try to claim (or imply) that their products are the same as genuine Diana Stalder brand, or just as good as Diana Stalder brand, or even the same formulations as genuine Diana Stalder products. None of that is true.
Some of these products ARE produced by the same parent company (the Stalder Group). The generic line of products known as "BCP" is manufactured by the Stalder Group for sale to dermatologists and salons around the Philippines, where they are often private labeled. But please understand that the ingredients and formulations are very different between these generic BCP products and the genuine Diana Stalder brand products. (By the way, the Stalder Group also manufactures several other brands of skin care products, but for some reason there don't seem to be as many unethical sellers making inappropriate claims about these other brands.)
The point is that these are are all very different brands and very different products. The BCP generic products are low-cost, basic products that are targeted at the cost-conscious consumer that wants a basic product at a low price. The wholesale prices for these products are low enough that small spas and salons in the Philippines can buy the products, private label them, mark them up and sell them at prices that still make sense in the Philippines. Genuine Diana Stalder products are premium formulations with maximum efficacy, targeted at the consumer who wants the very best, and is willing to pay for it.
It's similar in many respects to the situation with Toyota and Lexus. These cars are made by the same company, but they are very different products and distinct brands. The Toyota is for soemone who wants a basic car that is reliable transportation at a low price. The Lexus is for a customer that wants a premium, luxury product, and is willing to pay for the difference in quality, performance, luxury, etc. If a car dealership tried to sell Toyota Corollas by claiming they were really Lexus vehicles, well that would be unethical and the factory would no doubt revoke their dealership agreement.
Finally, I don't know your location, but I would note that it's illegal to sell generic, unlabeled cosmetics in the U.S. The FDA rules are pretty clear on this point.
To answer your specific question, there is nothing really that would prohibit you from using both the genuine Diana Stalder Black Beauty Bar and the Diana Stalder Glutathione Soap at the same time. Presumably you mean you would alternate between the two (e.g., one in the morning, and one a night). Of course if you over use it (use one, rinse, and then immediately use the other), you run the risk of drying out your skin.
Having said that, it's not clear to me why you would want to use both products at the same time. Generally, one will perform better than the other for whatever situation you are trying to address. If you have the classic problem of dark spots, acne scars, melasma, hyperpigmentation, etc. AND you want to be a whiter tone overall, we generally recommend to our customers that they first work on evening out the skin tone, THEN once that goal is achieved, work on overall whitening. So depending on the specifics of your case, that might mean first using the Diana Stalder Black Beauty Bar with a Surely White Lightening Cream (for your face) or Surely White Lightening Lotion (for the rest of your body). Then, when your tone has evened out, switching to the Glutathione Soap (or maybe the Papaya Kojic Soap) in comination with the Diana Stalder Surely White Whitening Cream and/or Surely White Body Whitening Lotion.
For the sake of full disclosure, I am the President of a company that sells genuine Diana Stalder products. In fact, we are the oldest and largest authorized distribution center for Diana Stalder products outside of the Philippines.
Regards,
Tim
