Hi, everyone! I am new here and I don't have any prior experience with formulating cosmetics.
I was thinking of making my own seborrheic dermatitis shampoo (and tonic, maybe) formula. Most commercially available shampoos include one or two active ingredients, sometimes not in very high concentrations.
I was thinking of making a formula that would include all main antifungal agents currently backed by evidence in the highest concentration allowed by European legislation. Such a list would possibly include, among others, ketoconazole (2%), piroctone olamine (1%), ciclopirox olamine (1.5%), climbazole (0.5%), and salicylic acid (3%). It seems somehow reasonable to assume that using all of these active ingredients together at maximum dosage would be more effective than using only one active ingredient.
However, my intuition tells me that there's probably something seriously wrong with my reasoning here since if it was a good idea somebody would've probably done it by now. I suppose it wouldn't be terribly difficult to make a product where 5-10% would consist of active ingredients, nor am I aware of any legislative issues of doing so. (Keep in mind I don't plan to create a product to sell, I am using legislation to guide what would be considered safe.)
So, my question would be: what am I missing?