Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
3. Household Chemistry
How do they make shampoo and conditioner in fragrant smells?
Shampoo without any perfumes would smell like the detergents it is made of. This is not a particularly pleasant smell. Even “unscented” products usually include a masking scent, which is a perfume designed to hide the odor of the other ingredients without having a lingering effect in the hair.
Coming up with a good perfume scent for a shampoo involves overcoming several obstacles—cost, stability, safety, color—and optimizing for the desired characteristics—a unique scent, how well the hair holds the scent, how the shampoo smells in the bottle, or how long the scent lasts.
With over 3,000 perfume elements to choose from, the perfumer will choose the much smaller set of scents desired for the shampoo. For example, it turns out that more people like fruitysmelling shampoos than other scents. The chemist will then select from that list the scents that work well with the other ingredients in the shampoo. Some scents will be destroyed or changed by the detergent and can’t be used. Other scents won’t dissolve well in the shampoo, or they won’t release from the shampoo well enough to be detected. Some of them will stick to the hair well, and others won’t.