Fig. 1.

Subcutaneous self-injection of a medicinal product in the anterior abdomen (a) using the “pinch-up” technique. The mean skin thickness is around 2.1 mm in the anatomic zones commonly used for subcutaneous injections (b); however, the target tissue (hypodermis) shows a wide variability in thickness. The absorption route of the administered molecules depends on their size (c), with molecules larger than about 16 kDa being mostly absorbed into lymphatic capillaries and those smaller than 1 kDa into blood capillaries [48]