Medical sunscreen lotion to bring in carry-on luggage on G trains

We were stopped in Shanghai Hongqiao station because in our luggage there was a sunscreen lotion can of 200 ml. They didn't allow us to travel with the lotion and we were obliged to make it send to our destination the day after. Actually we need that because it is a special lotion for the skincare of our son as a medical item. They told us that we could ask for a permission, as we're bound to take other G trains in the next few days. Where should we write or call to ask this permission?