Sprayed or vaporised products generate aerosols that can result in potential inhalation exposure of consumers using the product. As those products with propellant producing foam or soft gels are not suspected to emit inhalable aerosol, they are excluded from our further discussion. As defined by the German MAK commission, aerosols are multiphase systems of particulate solids or liquids Antidiabetic Compound Library screening dispersed in gases such as air (Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK

commission, 2010)). Aerosols include dusts, fumes and mists. Dusts consist of particles of solid matter generated by a mechanical process, or particles which have been agitated and dispersed in gases. Fumes are dispersions of very finely distributed solid matter in gases. They arise from thermal processes (e.g., welding fumes, metal (oxide) fumes, soot and flue ash) or chemical processes (e.g., the reaction of ammonia with hydrogen chloride). Mists are finely divided liquid droplets of a substance or mixture suspended in air with sizes generally ranging from 2 μm to 100 μm. They arise during nebulisation of liquids, http://www.selleckchem.com/products/Romidepsin-FK228.html during condensation from the vapour phase and during chemical processes (e.g., oil mist, hydrogen chloride in damp air). Due to the anatomical construction

of the respiratory tract, with a brighter lumen in the upper trachea and very small ones in the alveolar region, particle size of aerosol is a relevant parameter for the distribution of substances in compartments of the respiratory tract. The final particle size of a product aerosol is determined by the used ingredients and packaging details (e.g., spray nozzle, can size, etc.). Aerosols can consist of a

wide spectrum of particle sizes, i.e. larger particle sizes (>10 μm), exposure to which is limited to the upper respiratory tract and tracheobronchial tree, but also respirable particle sizes (<10 μm) which can reach deep lung regions (U.S. Department of Labor, MSHA, 2006). Understanding of particle size distribution else is essential for risk assessment since there is broad consensus in the scientific community for the following assumptions: • Significant absorption of inhaled substances can occur in all parts of the respiratory tract. The most important aspects of deposition of inhaled particles are shown in Fig. 1. Typically, propellant gas sprays may produce proportionate respirable particles or droplets <10 μm particle size (Bremmer et al., 2006a and Eickmann, 2007a), whereas pump sprays emit larger droplets in a non-respirable range >10 μm particle size. As mentioned above the particle/droplet size distribution is complex and depends on product formulation and the technical details of the applicator. Thus, independent of the spray category, the particle/droplet size spectrum can be modified in order to generate an optimized particle size distribution.