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A multiple homogeneous layer model was used to derive an estimate of dermal penetration for hydrotropes. The mathematical model simulates the uptake of a chemical substance through the skin into a central sink compartment below the skin. The model uses the substance's diffusion and partitioning coefficients and calculates the total (cumulative) fraction of the substance that enters the stratum corneum for a specific exposure duration. The model does not include any metabolism and the model is believed to represent an upper bound estimate of the potential uptake of the substance through the skin. The differential equations used to describe the model are numerically integrated using MATLAB software. 
Four exposure scenarios were modelled to derive exposure-specific uptake percentages. They included hand washing laundry, laundry pre-treatment, manual dish washing, and hard surface cleaning. These scenarios covered the product-relevant ranges of exposure durations and chemical concentrations.
Dermal penetration simulations based on a mechanistic model of the process of uptake of chemical substances in skin predicts that the dermal penetration of a generic hydrotrope is less than 0.6% of the applied amount (over a wide range of exposure scenarios). Simulations show that for an exposure extending to 23 hours, the dermal uptake does not exceed 2.8% of the applied amount, regardless of the applied amount (concentration) within the range of 0.0002% to 10%. 10% is considered an upper bound of the concentration of hydrotropes in consumer products. Irritation can be an issue at concentrations above 10% and so would need to be managed in the workplace.
Based on this state-of-science modelling, a 2.8% dermal absorption factor can be used as an upper bound value in general population exposure dose calculations for hydrotropes.

Key value for chemical safety assessment

Absorption rate - dermal (%):
2.8

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