Dye Laser Irradiation System for Investigations of Human Skin Reactions
Human skin responds to UV irradiation with erythema and pigmentation. This does not only happen under the influence of natural sunlight but also when skin is irradiated with UV while treating skin diseases or for cosmetic tanning. Dye lasers contribute to a better understanding of those reactions as they are ideal light sources because of their high spectral intensity, monochromaticity and wavelength tunability.
We set up an irradiation system consisting of an excimer pumped dye laser, a UV fibre optic system and a device to irradiate small skin areas of patients. Used for the irradiation of human skin the paramount property of the laser is its high spectral intensity. As high UV intensities were to be transmitted the fibre optic system was optimized. Another problem had to be solved: a homogeneous distribution of energy over the irradiated skin areas of about 0.5 cm diameter was needed. Therefore a special coupling method between laser and fibre was developed.
The volunteers’ skin reactions such as erythema and pigmentation were determined after irradiation with a colour measuring instrument (“chromameter”). These measurements were compared with data obtained in vitro from pure blood and melanine. For analyzing the measured data and estimating the skin reactions a computer programme was developed.
We determined the skin reactions in dependency of the irradiation wavelength in the range of 290 – 370 nm (action spectra) for various skin types. Very exact action spectra could be measured by using the specially adjusted chromameter. So a feasible method for the technical separation of UV dependent skin reactions was found and former data in literature could be corrected.
As well as that the temporary development of erythema and pigmentation was pursued after the irradiation. At the present we are trying to work out which molecular mechanisms in the skin interact with various UV wavelengths. For example, the presence of certain intermediates of the melanine metabolism play an important role for pigmentation in the UVA.