The skin barrier (1): The compact compound of callus cells, fats and moisture protects the skin against irritants such as bacteria, fungi or allergens. Barrier defect (2): If the skin lacks fats (lipids), it dries out and becomes cracked. Lipid deficiency is typical of mature skin, but also occurs in diabetes and neurodermatitis. Irritation (3): If the protective barrier is defective, bacteria, fungi and allergens can penetrate the skin, reproduce, and cause inflammation and infections. Symptoms (4): The skin's immune system reacts to these irritants with typical inflammation symptoms such as itching, burning skin and redness.