Vitamin C (VC; ascorbic acid, AA) is synthesised from glucose in the liver of most mammals, but not in humans. Synthetic AA supplementation is often necessary to prevent vitamin C deficiency. Intracellularly AA is reversibly oxidized to an ascorbic radical which converts into dehydroascorbic acid (DHA). Ascorbic acid crosses cell membranes with SVCT1, SVCT2 or GLUT1, GLUT3 and GLUT4 transporters. Recommended daily allowance for VC is around 75 mg/day for women and 90 mg/day for men. This seems to be too low in relation to real human body needs and does not ensure true health protection. There are ongoing studies re-evaluating the role of VC in cancer treatment. Therefore, it would be also appropriate to reassess its use as a specific drug in the prevention and therapy of asthma, allergic rhinitis and atopic dermatitis.