Cosmetic aerosols must balance performance with safety, and particle size sits at the core of this challenge. In one-way, small particles are normally related with a higher performance/sensorial, but on the other side they are more likely to be of inhaled and have deep lung deposition, raising questions about respiratory exposure and health effects. This presentation reviews the science behind aerosol particle size distribution and the regulatory frameworks that attempt to manage these concerns. It also examines formulation and packaging strategies that maintain product efficacy while minimizing exposure to potentially hazardous ultrafine particles. Ultimately, the particle size dilemma underscores the need for harmonized standards, improved measurement methodologies, and a more comprehensive understanding of the health implications of aerosolized cosmetic ingredients.