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 fruity smelling 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 adhere to the hair well, and others won’t.

Many perfumes are made of essential oils. Here the word essential does not mean that you can’t do without it, but instead refers to the fact that the oil was extracted from a flower, fruit, or some other thing as an essence. This is often done by heating the material until it boils, and then collecting and condensing the vapors (distilling). Other methods are solvent extraction, where the material is crushed in a solvent such as alcohol to dissolve the oils, and chromatography, where the oils wick up in a substance and separate out according to how fast they travel.

There may be 300 different compounds in an essential oil. Usually there is one or more molecules that give it its characteristic odor. These molecules can be used by themselves instead of the essential oil to reduce cost or ensure reproducibility and stability in the final product.

Some examples of molecules that have characteristic scents are shown below.

Vanillin (Vanilla scent)

Limonene (citrus scent)

Carvone (spearmint scent)

Methyl Salicylate (Wintergreen scent)

Isoamyl Acetate (banana scent)

Ethyl Isovalerate (apple scent)