The Same Ingredient, Four Ways

This layer assumes you already know what the ingredient does. The problem it solves is the one in the shop: four bottles, all of them saying vitamin C, at four prices, and no obvious reason to prefer any of them.

Form, strength, percentage, pH and formulation are what separate them, and each of those decides who a bottle is actually for. If any of that reads as unfamiliar, the six basics modules cover the groundwork first.