INTRODUCTION
Intradermal therapy, or mesotherapy, refers to the direct administration of active drugs into target tissues by means of intradermal microinjections. This technique was introduced in 1952 by the French physician Dr. Michel Pistor.1 The term “meso” refers to the mesoderm, meaning the embryonic middle layer located between the ectoderm and endoderm. All the connective tissues that form the dermis are derived from this embryonic middle layer, and it is into this middle layer that drugs are injected when intradermal therapy techniques are applied. Intradermal therapy is now recognized by the French Health Insurance as an integral part of therapeutic modalities, as it is in numerous other European countries, with this medical discipline currently taught in leading European and American universities.2 In 1976, the First International Conference on Mesotherapy was held, and in 1982, the International Mesotherapy Society (IMS) was created by Dr. Michel Pistor, Dr. Carlo Alberto Bartoletti, and Dr. Gilbert Ravily. IMS encompasses 15 member countries and aims to improve intradermal therapy practices and procedures as a whole. In brief, there are essentially four different injection techniques, which correspond to four different injection depths.3 The crucial question underlying our research was the following: Do the technical terms used to refer to the injection technique actually correspond to the scientific depth of injection attained whilst the injection is actually performed.4This publication sought to prove by means of mathematical and visual methods that the technical terms used to refer to intradermal therapy injections are incorrect when considering the true depth of the actual injection performed. This holds true for general practice, but appears even more pertinent in terms of esthetic medicine, particularly that involving the face, hands, and décolleté.In both general practice and esthetic medicine, four types of injection techniques are used depending on the definitions of the different intradermal therapy injections, meaning the used needle length and gauge, the depth of penetration, and the components of the injected layer.Intra-Epidermal Injection (IED). This is technically not an injection but rather a mild brush of the stratum corneum with the needle bevel.5 The basal layer of the skin is not penetrated. To avoid scar formation, the needle is mostly parallel to the skin, with the bevel of the needle usually facing upwards (Figure 1).Superficial Intradermal Injection (IDS). This is actually the technique invented by Dr. Pistor in the 1950’s, considered to be the gold standard for intradermal therapy. This technique is also referred to as picotage or nappage, the latter being derived from the French and meaning “covering”. For this technique, a papule is created resulting from the injection at the epidermis-dermis junction at 1-2mm depth (Figure 2). The bevel is theoretically oriented downwards during the injection, though it may also be oriented upwards, the decision between “up” and “down”
