Organic solvents pass the cutaneous barriers and may quickly be absorbed in substantial amounts, such that several solvents have "skin" denotations in lists of occupational exposure limit values. Solvents may be absorbed from liquids, upon direct skin contact, and in some cases also from contact with vapors. Environmental factors such as temperature, humidity, vehicle, and ventilation influence absorption. Absorption rates vary considerably; several amphiphilic solvents are absorbed at high rates. Since solvents are volatile, unoccluded repeated exposures result in less absorption than does continuous contact, and adequate ventilation may reduce absorption considerably. Risk assessments of skin absorption of organic solvents have benefited from calculation of quantitative structure-activity relationships based on log P(o/w), which enables skin absorption to be calculated with reasonable accuracy.