Biophysical aspects of contact dermatitis and its prevention

Abstract

The skin, one of the largest organs of the body, is composed of three layers: the epidermis, dermis and subcutis. The outer most part of the epidermis i.e., the stratum corneum - serves as a protective barrier between the individual and the environment, defending the body from mechanical injuries, foreign chemical substances, microbes and loss of water. Both inherited and acquired abnormalities of the stratum corneum may increase the sensitivity of the skin to environmental factors and predispose it to the development of irritant or allergic contact dermatitis. Such a diagnosis is based on the medical history, clinical examination and appropriate patch testing. However, the reading of patch tests is subjective, provides qualitative information and the results depend largely on the investigator's experience. To obtain objective, comparable data, various bioengineering techniques have been designed to evaluate various aspects of the skin s response.

In this Thesis, we used visual scoring together with several established non-invasive methods (transepidermal water loss, Corneometer, laser Doppler) and a new one (electrical impedance) to assess the irritant and allergic contact reactions, the effects of the treatment on skin sensitivity and skin dryness.

In Paper I, we used the above-mentioned techniques to evaluate clinically similar allergic (to NiSO4 in distilled water in different concentrations) and irritant (to 2% sodium lauryl sulphate) skin reactions in 19 nickel-allergic patients.

In Paper II, patch tests with 0.5% and 2% NiSO4 in petrolatum were done on the forearm of 20 nickel-allergic patients and five healthy subjects, which had been pre-treated with a urea-containing moisturiser. Skin areas that had not been pre-treated were used for comparisons.

In Paper III, 2% sodium lauryl sulphate and 40% non-anoic acid were used by two independent laboratories to induce irritant contact reactions in 40 healthy volunteers.

In Paper IV, the dry skin of the lower legs of 24 healthy elderly subjects was treated twice daily with two identical creams, one of which contained urea and sodium chloride and the other urea alone.

In Paper V, 2 % sodium lauryl sulphate in distilled water was used to produce irritant contact dermatitis in 29 eczema patients and 19 healthy controls.

The main conclusion of this thesis is that bioengineering techniques give descriptive, detailed information about pathophysiological changes in the skin of patients. Our data suggest that, in addition to well-established biophysical methods, this new impedance technique is of value for experimental studies of contact dermatitis. However, more investigations are needed before it can be used in routine diagnostic work, e.g., technical refinement and the development of guidelines for impedance measurements.