Methods for investigating contact eczematous patients and for measuring the sensitizing potential of various substances are well known and in general, sufficiently effective. This is not true for irritant dermatitis, or for possible (skin) irritant substances; moreover, cosmetics commonly do not contain acutely harmful ingredients. The use of various instrumental measurements (insensible H2O loss, CO2release, electrical impedance, sweat rate) as indicators of the irritant potentials of substances is advocated. At the same time it is suggested that the factory physician actively investigate the workers in his factory, since these workers are exposed to known substances in known concentrations and combinations, possibly fur extensive periods. This may prove to be part of a new role for him. A cosmetic may be one of several factors increasing impairment and only beyond a certain limit may this result in overt disease. Below that limit the health reserve is only partially depleted. Whether this is harmful to a person depends on other stresses, such as medicaments, work materials, other cosmetics and environmental chemicals. The effect of these must also be quantified. A model of these cumulative stresses and reactions is presented and discussed.