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Publications › 1/2010, 2/2010, 3/2010, 4/2010, 1/2012

The determination of the RSF starts with the generation of free radicals by a defined number of photons characterized by irradiance and irradiation time followed by the measurement of the Radical Response. The skin is treated with the radical indicator, the nitroxides 2,2,5,5 tetrametylpyrrolidine-N-oxyl(PCA). Different free radicals (O2 –•, • OH – , L•, LO•, LOO•) were generated by UV irradiation and react with PCA decreasing its amplitude. Corresponding to a numerical algorithm over a time interval of 5 min 6 data points (0’ ,30”, 1', 2’, 3’, 5’) were measured. The different time interval corresponds to different UV-doses . The measurements are expressed in SED (standard erythema dose), where 1SED = 100 J/m2 normalized to 298 nm ). The k-factor (reaction velocity) of the reduction curve was estimated. The number of free radicals generated in the skin is direct proportional to the k-factor. A calibration curves for three different density filters (PF = 1, PF = 10 and PF = 50)is measured. The density filters were supplied from ORIEL Instruments (USA). An optical density filter is a thin qauartz plate provided with a corresponding vacuum deposited metal alloy resulting in an attenuation of the transmittance. PF = 10 means an attenuation to 1/10 of the incident light. For 6 (n = 6) different optical density filters (PF1, PF2 , PF 5; PF 10, PF 20 and PF 50) calibration curves were measured and normalized to the full light intensity(nonirradiated case). A second calibration curve k1 / kn = RSFn of skin is determined. This curve correlates with the curve of decreased irradiance I )

N(free radicals in untreated skin) = RSF
N(free radicals in treated skin)
N(R • in treated skin) = N (R • in untreated skin) / RSF

It is the basis for the determination of the RSF of an unknown sunscreen which is measured as a comparison with this calibration curve.
On the basis of this observation it is possible to present the relation between the RSF and the number of corresponded free radicals. The so called second calibration curve documents this correlation. For radical protection the curve corresponds to a 1/x-function which is also applied to radical promotion.


Processes or substances which increase the number of generated free radicals are characterized by RSF < 1 and which decrease the number of generated free radicals are characterized by RSF > 1. The normal untreated skin is characterized by a RSF = 1and the number of measured free radicals corresponds to a concentration of 100 %. All products which can characterized by RSF > 1are radical protectors. Products which labelled by RSF < 1 are radical promoters.