What type of ingredient does not have to appear on a product's ingredient label?

Fragrance is an ingredient that is often allowed to remain unspecified on product labels, as it can be considered a trade secret. This means manufacturers are not required to disclose the specific components that make up the fragrance, allowing them to protect proprietary formulas. In contrast, surfactants, preservatives, and emollients must be listed because they play crucial roles in the product's performance and safety. Surfactants interact with water to help cleanse or emulsify ingredients, preservatives prevent microbial growth, and emollients provide moisturization and skin barrier support, all of which are essential for consumer safety and efficacy.

Thus, while fragrances contribute to the sensory appeal of a product, their classification allows for some flexibility in labeling, distinguishing them from the other categories of ingredients that must be clearly stated.