**1. An overview on the original mesotherapy technique for dermatological uses**

The aim behind mesotherapy was to create a new technique, which favors the supplementation of needed agents directly and locally to the site of complaint. As previously mentioned, the proposed theory by *Pistor* depends mainly on the direct effect of the used drug on the tissue originating from the mesoderm [1, 2]. The mesoderm is one of the primary germ layers of the embryo that is responsible for the development of skin, connective tissue, muscles, tendons, and circulatory system. It is mainly responsible for skin vitality and health [3]. The injection technique of mesotherapy depends mainly on the anatomical, histological and geometrical landmarks of the target tissues. Mesointerface is the horizontal interface between the injected agents and the injected region. For maximum benefits, the injected surface is inversely proportional to the amount and molecular weight of the injected agent. The wider the mesointerface is, the greater the number of the dermal receptors that are activated [4].

On the other hand, the vertical component depends on the depth of penetration. Mesotherapy could be injected in the epidermis, dermis, or subcutaneous [1]. The more superficial injection is, the longer the drug remains in the tissue. It permits sustained release of the drug with slow and progressive diffusion into the surrounding tissues [2, 5, 6].

The technique depends on the skin characteristics and components. It determines the type of drug injected, the technique of injection, and the drug dosage. The skin has a natural sustained releasing property. Therefore, the nature of the skin determines the layers that are suitable for injection. The injection process must be in the superficial layers (intradermal) for the drug to remain as long as possible and for its clearance to become slower. If the drug is injected deeper, its clearance becomes faster. So the more superficial the injection is, the longer the drug remains in place (being far more powerful and efficient) [6].
