Comparative study of the density of particles in suspensions for patch testing

A simple and reliable method to evaluate the density of particles in patch test suspensions is described. The number of particles per unit volume has been found to vary significantly within a wide range of values. These variations have no relation to the concentration or the molecular weight of the substance, as far as particles larger than 10 micron are concerned. Because the presence of particles is one of the factors which can influence percutaneous penetration and since physical manipulations are able to modify the size of these particles, it is suggested that the kinetics of penetration of haptens through the skin should be revaluated with regard to this special point.