INTRODUCTION
A wide-sweeping adoption of soft tissue fillers for use in aesthetic medicine has occurred since the introduction of bovine collage in 1981 and then hyaluronic acid (HA)-based products in 1995.1-6 With a panoply of options for HAs now available for aesthetic physicians, dermal fillers products offer treatment options for cosmetic correction of facial lines and wrinkles. Regardless of which filler is being introduced to the medical community, one topic has been an abiding source of interest for some years: depth of injection in the dermis.
Manufacturer instructions as well as in-service education from colleagues nearly always contain directions that any dermal filler product is to be injected at various depths in the skin’s dermis (Figure 1).3-6
Many of us may not know the precise depth of various skin strata. To that end, in this paper we present data a) to identify the depths of the strata; b) explore whether the angle of penetration is appropriate for the stratum selected; and c) argue that the injection depth can be more targeted than we had originally assumed. Data reported have been gathered from ultrasound imaging, biopsies, live injections, and mathematical calculations. Areas of injection and measurement include the nasolabial folds and buttocks in the superficial reticular and/or mid dermis.
Epidermis
This layer consists of stratified squamous epithelial cells. Its mean thickness varies from 0.10 to 0.15 mm, depending on area of the body. Facial skin, for example, is ordinarily thinner than skin on the soles of the feet.
Dermis
This stratum has 2 different layers: the papillary dermis and the reticular dermis, both of special interest for injectors. Each of the layers has a well-defined histological specificity. In the papillary dermis, collagen and elastic fibers are thin and usually somewhat perpendicular to the basal epidermal layer.
In contrast, the reticular dermis is considerably thicker than papillary dermis. Its fibers are more horizontal, ie, more parallel than perpendicular to the basal epidermal layer, unlike the perpendicular ones of the papillary dermis. The thickness of the reticular dermis varies from one body area to another. Della Volpe et al7 show dermis thicknesses of 2.56 mm for the check and 2.79 mm for the buttock. For the epidermis and the dermis, the thicknesses are 2.72 mm and 2.93 mm, respectively. On certain areas of the dorsum (eg, the back side of the neck and the back), however, the thickness may reach 10.0 mm.
The reticular dermis may be arbitrarily divided in equivalent thirds: superficial reticular dermis, mid reticular dermis, and deep reticular dermis. In our practice, when using HAs, we
