An ingredient leaving a formulation, entering skin and remaining at a particular site are different processes. tiptop defines delivery in separate stages within ATDS so that research objectives and technical statements refer to clear locations, quantities and times.
Five processes, each with its own subject of observation
| Process | What ATDS examines |
|---|---|
| Release | An ingredient leaves the final formulation and becomes available for subsequent delivery |
| Skin entry | Movement from the skin surface into the stratum corneum or other skin layers |
| Local deposition or retention | Detection in an intended skin layer or follicular compartment, with persistence for a period of time |
| Skin permeation | Passage through skin tissue to the other side or into the receptor fluid of an in vitro apparatus |
| Systemic absorption | Entry into the human circulatory system |
We record these processes separately because the skin surface, individual layers, follicles and circulation pose different research questions. An observation at a particular location has its own defined scope.
Set the target before selecting an evaluation
ATDS uses in vitro release testing (IVRT) to examine how ingredients leave a formulation. In vitro permeation testing (IVPT) uses skin as a barrier to examine distribution and passage within the test system. Patch testing and related evaluations observe local reactions; human use studies record actual performance under specified conditions.
We use these distinctions to design studies so that each evaluation answers its own question. Release data must connect with distribution within skin. Discussion of systemic absorption in humans requires evidence directly addressing circulation.
Bring quantity, location and time together
Higher-level delivery evaluation combines quantification, spatial localization and mass balance. Mass balance records how much of the material introduced into a system is ultimately recovered at each location, complementing images and readings at different time points.
Particle size, distribution, zeta potential, morphology and concentration describe quality attributes of materials and formulations. We manage these separately from skin-layer location, delivered quantities and human performance, then establish their relationships in the finished product.
Publishing these definitions gives “delivery” a clear and consistent meaning in tiptop’s technical information. The full framework appears in ATDS 2026.