A small sample or a large supply
Topical studies sometimes describe a finite dose or an infinite dose. Finite means the experiment uses a limited amount. Infinite is a laboratory term for an amount large enough to act as an ongoing supply during the test. It does not literally mean an endless bottle.
Why the distinction matters
These setups answer different questions about movement through a test barrier. A large supply kept against a sample is not the same situation as a small amount applied once. Researchers choose the setup for their purpose, and the result needs to be read with that choice in mind. A paper comparing these approaches used in vitro experiments, meaning tests outside a living person.
Keep lab amounts out of home directions
Do not copy a laboratory dose onto your skin or assume more product will reproduce a graph. The tested formula, barrier, contact conditions, and measurements all matter. A finished product has its own directions. When reading a study, look for the amount applied and whether the researchers explain its purpose. That detail can be more useful than an impressive percentage lifted out of the results table.
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