One of the most significant changes introduced by the Scientific Committee on Consumer Safety (SCCS) in the Notes of Guidance with the eleventh revision of March 2021 is the use of two mathematical models for the calculation of inhalation exposure.
Cosmetic products, by definition, are designed to be applied to the external surfaces of the human body, teeth and mucous membranes of the mouth. However, sometimes these products, or some of the ingredients that compose them, can be inhaled in the form of vapours, powders and aerosols.
The first model applies to products that can generate vapours (for example liquid products that contain volatile solvents). For these products, the inhalation Systemic Exposure Dose (SEDinh) of the ingredients is calculated by multiplying the daily exposure to the product by the concentration and evaporation fraction (a value between 0 and 1).
The second model applies to powder and spray products. Spray products fall into two categories: propellant sprays (which produce a finer aerosol) and pump sprays (which produce a less fine and more difficult to inhale aerosol).
For the assessment of inhalation exposure to these types of products, the SCCS proposed the use of a 1- or 2-Box model.
In a classical 1-Box model it is assumed that the entire spray amount is instantaneously released into the air and distributed in a box of a specific size, which e.g. simulates the breathing zone. The resulting air concentration is then multiplied by the breathing rate and the time spent in the box to calculate the exposure. A 2-Box model takes into account the dilution of the substance over time. As in the 1-Box model, the assumption is that the spray is instantly released and distributed in a box around the head. There the aerosol is present for exposure over a defined time, after which the full amount of aerosol in the first box is transferred to a larger second box (representing a room where the product is used), where it is available for inhalation for a second defined time period. For a conservative approach, the air exchange (fresh air getting in, exhaust air getting out) can be assumed as zero.
In addition to the size of the two boxes and the time that the product remains in suspension, the size of the aerosol generated by the product must also be taken into account for the calculation of the SEDinh, which vary according to the type of spray used. A finer aerosol is more easily breathable and consequently the substances contained within will be more systemically available.
The application of these mathematical models allows a better characterization of exposure to the ingredients contained within cosmetic products and is a further step towards a greater guarantee of safety for the final consumer.
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