Skin sensitivity testing : a biophysical approach

The skin is regarded as the largest organ of the body, although it is only a few millimetres thick; it is also the interface between the environment and the body's vital structures. Its large surface area is constantly exposed to physical factors, allergens, irritants and infectious agents. Contact dermatitis, an inflammation of the skin caused by contact with exogenous substances, is by far the commonest reaction of the skin when exposed. This diagnosis accounts for about 10% of all visits to a dermatologist and for 80% of all occupational skin diseases. The mechanism of action by which the exogenous chemical causes inflammation may be immunological and the reaction is than called allergic contact dermatitis, but if it is not immunological, the reaction is called irritant contact dermatitis. The initial triggering event for both these reactions may differ, but the clinical picture of irritant and allergic disease is similar. Medical history and clinical examination are the principal tools of the clinical dermatologist. In some cases, punch biopsy and microscopy give more detailed information. Objective and non-invasive methods are needed to assess skin reactions in clinical work and research. Various devices for non-invasive evaluation of the skin have become available. In our studies, we have compared a new bioengineering technique, based on electrical impedance, with more established methods, such as Transepidermal Water Loss, Electric Capacitance moist measurements, laser Doppler flowmetry and visual evaluation. In paper I, sodium lauryl sulphate solutions (SLS) (0.1-5.0%) and a blank were applied to the skin of 10 healthy volunteers. In paper II, readings were taken from ten regions over the body in 131 healthy volunteers, divided into four groups on the basis of age and gender. In paper III, nickel sulphate in distilled water at various concentrations (0.15%, 0.31%, 0.62%, 1.25% and 2.5%) and 2% SLS were used to induce contact dermatitis of allergic and irritative type by using them on 33 healthy volunteers. In paper IV, 0.1 mI tuberculin was injected intracutaneously in one arm and 2 % SLS in distilled water was applied to the volar aspect of the other arm on 20 healthy subjects. In paper V, skin prick tests were performed with relevant allergens and histamine in 10 patients with a history of hay fever or mild asthma. The main conclusion of this thesis is that, compared to visual scoring, further relevant information about experimentally-induced skin reactions is obtained, by the use of noninvasive bioengineering techniques, especially in combination. Our data support the view that non-invasive bioengineering techniques, including a newly developed impedance instrument, will improve the clinical management of various dermatological conditions in the future